Bacteriophage Ecology Group – Cyanophage References

	Bacteriophage Ecology Group Cyanophage References
	Dedicated to the ecology and evolutionary biology of the parasites of unicellular organisms (UOPs)
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© Phage et al.	last updated on Sunday, July 11, 2004

The physical environment affects cyanophage communities in British Columbia inlets. Frederickson,C.M., Short,S.M., Suttle,C.A. (2003). Microb. Ecol. 46:348-357. Little is known about the natural distribution of viruses that infect the photosynthetically important group of marine prokaryotes, the cyanobacteria. The current investigation reveals that the structure of cyanophage communities is dependent on water column structure. PCR was used to amplify a fragment of the cyanomyovirus gene (g) 20, which codes for the portal vertex protein. Denaturing gradient gel electrophoresis (DGGE) of PCR amplified g20 gene fragments was used to examine variations in cyanophage community structure in three inlets in British Columbia, Canada. Qualitative examination of denaturing gradient gels revealed cyanophage community patterns that reflected the physical structure of the water column as indicated by temperature and salinity. Based on mobility of PCR fragments in the DGGE gels, some cyanophages appeared to be widespread, while others were observed only at specific depths. Cyanophage communities within Salmon Inlet were more related to one another than to communities from either Malaspina Inlet or Pendrell Sound. As well, surface communities in Malaspina Inlet and Pendrell Sound were different when compared to communities at depth. In the same two locations, distinct differences in community composition were observed in communities that coincided with depths of high chlorophyll fluorescence. The observed community shifts over small distances (only a few meters in depth or inlets separated by less than 100 km) support the idea that cyanophage communities separated by small spatial scales develop independently of each other as a result isolation by water column stratification or land mass separation, which may ultimately lead to changes in the distribution or composition of the host community. [TOP OF PAGE]
Bacterial photosynthesis genes in a virus. Mann,N.H., Cook,A., Millard,A., Bailey,S., Clokie,M. (2003). Nature 424:741 A bacteriophage may protect itself and its host against a deadly effect of bright sunlight. [TOP OF PAGE]
Phages of the marine cyanobacterial picophytoplankton. Mann,N.H. (2003). FEMS Microbiol. Rev. 27:17-34. Cyanobacteria of the genera Synechococcus and Prochlorococcus dominate the prokaryotic component of the picophytoplankton in the oceans. It is still less than 10 years since the discovery of phages that infect marine Synechococcus and the beginning of the characterisation of these phages and assessment of their ecological impact. Estimations of the contribution of phages to Synechococcus mortality are highly variable, but there is clear evidence that phages exert a significant selection pressure on Synechococcus community structure. In turn, there are strong selection pressures on the phage community, in terms of both abundance and composition. This review focuses on the factors affecting the diversity of cyanophages in the marine environment, cyanophage interactions with their hosts, and the selective pressures in the marine environment that affect cyanophage evolutionary biology. [TOP OF PAGE]
Genetic diversity and temporal variation in the cyanophage community infecting marine Synechococcus species in Rhode Island's coastal waters. Marston,M.F., Sallee,J.L. (2003). Appl. Environ. Microbiol. 69:4639-4647. The cyanophage community in Rhode Island's coastal waters is genetically diverse and dynamic. Cyanophage abundance ranged from over 10(4) phage ml(-1) in the summer months to less then 10(2) phage ml(-1) during the winter months. Thirty-six distinct cyanomyovirus g20 genotypes were identified over a 3-year sampling period; however, only one to nine g20 genotypes were detected at any one sampling date. Phylogenetic analyses of g20 sequences revealed that the Rhode Island cyanomyoviral isolates fall into three main clades and are closely related to other known viral isolates of Synechococcus spp. Extinction dilution enrichment followed by host range tests and PCR restriction fragment length polymorphism analysis was used to detect changes in the relative abundance of cyanophage types in June, July, and August 2002. Temporal changes in both the overall composition of the cyanophage community and the relative abundance of specific cyanophage g20 genotypes were observed. In some seawater samples, the g20 gene from over 50% of isolated cyanophages could not be amplified by using the PCR primer pairs specific for cyanomyoviruses, which suggested that cyanophages in other viral families (e.g., Podoviridae or Siphoviridae) may be important components of the Rhode Island cyanophage community. [TOP OF PAGE]
[Development of cyanobacterial phages at the Institute of Microbiology and Virology of the National Academy of Sciences of Ukraine (History and perspectives)]. Mendzhul,M.I., Lysenko,T.G., Syrchin,S.A. (2003). Mikrobiol. Zh. 65:133-140. The paper deals with the basic trends of fundamental investigations of the Department of Algae Viruses in the field of cyanophagia-ecology, biological and physico-chemical properties of cyanophages as well as interrelation with the host cells. Such problems as a possibility to use the system cyanophage-cyanobacteria as the experimental model for development of the unified functional model of productive infection, efficient methods of prophylaxis and therapy of virus infections as well as the solution of various biotechnological problems are discussed. [TOP OF PAGE]
[Comparative characteristics of native proteinases of the cyanobacteria Plectonema boryanum and Anabaena variabilis and those induced by cyanophages]. Mendzhul,M.I., Perepelytsia,S.I. (2003). Mikrobiol Zh 65:21-28. Physico-chemical and catalytic properties of proteinases of native and induced cells of cyanobacteria Plectonema boryanum have been comparatively studied. It has been established that at early stages of reproduction of cyanophage LPP-3 in cyanobacteria P. boryanum is formed de novo proteinase complex consisting at least of five enzymes. Proteinases induced by the virus are distinguished from those of native cells by a series of physico-chemical characteristics and possess higher catalytic activity. Analogous virus-induced changes in proteinase complex also occur in the system cyanobacterium Anabaena variabilis--cyanophage A-1. Possible functions of certain enzymes of proteinase complex in the virus pathology of cyanobacteria cells are discussed in the paper. [TOP OF PAGE]
Cyanophages infecting the oceanic cyanobacterium Prochlorococcus. Sullivan,M.B., Waterbury,J.B., Chisholm,S.W. (2003). Nature 424:1047-1051. Prochlorococcus is the numerically dominant phototroph in the tropical and subtropical oceans, accounting for half of the photosynthetic biomass in some areas. Here we report the isolation of cyanophages that infect Prochlorococcus, and show that although some are host-strain-specific, others cross-infect with closely related marine Synechococcus as well as between high-light- and low-light-adapted Prochlorococcus isolates, suggesting a mechanism for horizontal gene transfer. High-light-adapted Prochlorococcus hosts yielded Podoviridae exclusively, which were extremely host-specific, whereas low-light-adapted Prochlorococcus and all strains of Synechococcus yielded primarily Myoviridae, which has a broad host range. Finally, both Prochlorococcus and Synechococcus strain-specific cyanophage titres were low (< 10(3) ml(-1)) in stratified oligotrophic waters even where total cyanobacterial abundances were high (> 10(5) cells x ml(-1)). These low titres in areas of high total host cell abundance seem to be a feature of open ocean ecosystems. We hypothesize that gradients in cyanobacterial population diversity, growth rates, and/or the incidence of lysogeny underlie these trends. [TOP OF PAGE]
Genomic sequence and evolution of marine cyanophage P60: a new insight on lytic and lysogenic phages. Chen,F., Lu,J. (2002). Appl. Environ. Microbiol. 68:2589-2594. The genome of cyanophage P60, a lytic virus which infects marine Synechococcus WH7803, was completely sequenced. The P60 genome contained 47,872 bp with 80 potential open reading frames that were mostly similar to the genes found in lytic phages like T7, fYeO3-12, and SIO1. The DNA replication system, consisting of primase-helicase and DNA polymerase, appeared to be more conserved in podoviruses than in siphoviruses and myoviruses, suggesting that DNA replication genes could be the critical elements for lytic phages. Strikingly high sequence similarities in the regions coding for nucleotide metabolism were found between cyanophage P60 and marine unicellular cyanobacteria. [TOP OF PAGE]
Prokaryotic and viral diversity patterns in marine plankton. Fuhrman,J.A., Griffith,J., Schwalbach,M. (2002). Ecol. Res. 17:183-194. Prokaryotes and viruses play critical roles in marine ecosystems, where they are both highly abundant and active. Although early work on both prokaryotes and viruses revealed little of their diversity, molecular biological approaches now allow us to break apart these 'black boxes.' The most revealing methods have been cloning and sequencing of 16S rRNA genes, community fingerprinting (such as terminal restriction fragment length polymorphism; TRFLP), and fluorescent in situ hybridization. Viral diversity can now be analyzed by pulsed field gel electrophoresis (PFGE) of viral genomes. The present paper summarizes recent advances in bacterial and virus diversity studies, and presents examples of measurements from polar, tropical, and temperate marine waters. Terminal restriction fragment length polymorphism shows that many of the same operationally defined prokaryotic taxa are present in polar and tropical waters, but there are also some unique to each environment. By one measure, a sample from over a Philippine coral reef had about 100 operationally defined taxa, whereas one from the open tropical Atlantic had about 50 and from the icy Weddell Sea, about 60. Pulsed field gel electrophoresis of two depth profiles, to 500 m, from Southern California, measured 2 months apart, shows striking similarities in viral genome length diversity over time, and some distinct differences with depth. The euphotic zone samples had extremely similar apparent diversity, but samples from 150 m and 500 m were different. An obvious next step is to compare the bacterial and viral diversity patterns, because theory tells us they should be related. [TOP OF PAGE]
Observations on cyanobacterial population collapse in eutrophic lake water. Gons,H.J., Ebert,J., Hoogveld,H.L., van den Hove,L., Pel,R., Takkenberg,W., Woldringh,C.J. (2002). Antonie van Leeuwenhoek 81:319-326. In two laboratory-scale enclosures of water from the shallow, eutrophic Lake Loosdrecht (the Netherlands), the predominating filamentous cyanobacteria grew vigorously for 2 weeks, but then their populations simultaneously collapsed, whereas coccoid cyanobacteria and algae persisted. The collapse coincided with a short peak in the counts of virus-like particles. Transmission electron microscopy showed the morphotype Myoviridae phages, with isometric heads of about 90 nm outer diameter and > 100-nm long tails, that occurred free, attached to and emerging from cyanobacterial cells. Also observed were other virus-like particles of various morphology. Similar mass mortality of the filamentous cyanobacteria occurred in later experiments, but not in Lake Loosdrecht. As applies to lakes in general, this lake exhibits high abundance of virus-like particles. The share and dynamics of infectious cyanophages remain to be established, and it is as yet unknown which factors primarily stabilize the host-cyanophage relationship. Observations on shallow, eutrophic lakes elsewhere indicate that the cyanophage control may also fail in natural water bodies exhibiting predominance of filamentous cyanobacteria. Rapid supply of nutrients appeared to be a common history of mass mortality of cyanobacteria and algae in laboratory and outdoor enclosures as well as in highly eutrophic lakes. [TOP OF PAGE]
[Action of Spirulina platensis on bacterial viruses]. Gorobets,O.B., Blinkova,L.P., Baturo,A.P. (2002). Zh. Mikrobiol. Epidemiol. Immunobiol. 18-21. The impact of the biomass of the blue-green microalga (cyanobacterium) S. platensis on bacteriophage T4 (bacterial virus) has been evaluated. The study revealed that the addition of S. platensis biomass into the agar nutrient medium, followed by sterilization with 2% chloroform and thermal treatment, produced an inhibiting or stimulating effect on the reproduction of the bacteriophage in Escherichia coli B cells, depending on the concentration of S. platensis and the multiplicity of phage infection, as well as on the fact whether the microalgae were added during the first cycle of the development of the virus. The reproduction of the bacteriophage in E. coli B was influenced by the method and duration of the sterilization of the nutrient medium with S. platensis. [TOP OF PAGE]
Use of signal-mediated amplification of RNA technology (SMART) to detect marine cyanophage DNA. Hall,M.J., Wharam,S.D., Weston,A., Cardy,D.L.N., Wilson,W.H. (2002). BioTechniques 32:604-611. Here, we describe the application of an isothermal nucleic acid amplification assay, signal-mediated amplification of RNA technology (SMART), to detect DNA extracted from marine cyanophages known to infect unicellular cyanobacteria from the genus Synechococcus. The SMART assay is based on the target-dependent production of multiple copies of an RNA signal, which is measured by an enzyme-linked oligosorbent assay. SMART was able to detect both synthetic oligonucleotide targets and genomic cyanophage DNA using probes designed against the portal vertex gene (g20). Specific signals were obtained for each cyanophage strain (S-PM2 and S-BnMI). Nonspecific genomic DNA did not produce false signals or inhibit the detection of a specific target. In addition, we found that extensive purification of target DNA may not be required since signals were obtained from crude cyanophage lysates. This is the first report of the SMART assay being used to discriminate between two similar target sequences. [TOP OF PAGE]
Plankton blooms: Lysogeny in marine Synechococcus. McDaniel,L., Houchin,L.A., Williamson,S.J., Paul,J.H. (2002). Nature 415:496 Viral infection of bacteria can be lytic, causing destruction of the host cell, or lysogenic, in which the viral genome is instead stably maintained as a prophage within its host. Here we show that lysogeny occurs in natural populations of an autotrophic picoplankton (Synechococcus) and that there is a seasonal pattern to this interaction. Because lysogeny confers immunity to infection by related viruses, this process may account for the resistance to viral infection seen in common forms of autotrophic picoplankton. We undertook a seasonal study in Tampa Bay, Florida, of prophage induction in cyanobacteria over the year ending in October 2000 to find out whether lysogeny occurs in natural Synechococcus populations and, if so, how it is affected by changing environmental conditions. [TOP OF PAGE]
Lysogeny and lytic viral production during a bloom of the cyanobacterium Synechococcus spp. Ortmann,A.C., Lawrence,J.E., Suttle,C.A. (2002). Microb. Ecol. 43:225-231. Lytic viral production and lysogeny were investigated in cyanobacteria and heterotrophic bacteria during a bloom of Synechococcus spp. in a pristine fjord in British Columbia, Canada. Triplicate seawater samples were incubated with and without mitomycin C and the abundances of heterotrophic bacteria, cyanobacteria, total viruses and infectious cyanophage were followed over 24 h. Addition of mitomycin C led to increases in total viral abundance as well as the abundance of cyanophages infecting Synechococcus strain DC2. Given typical estimates of burst size, these increases were consistent with 80% of the heterotrophic bacteria and 0.6% of Synechococcus cells being inducible by the addition of mitomycin C. This is the highest percentage of lysogens reported for a natural microbial community and demonstrates induction in a marine Synechococcus population. It is likely that the cyanophage production following the addition of mitomycin C was much higher than that titered against a single strain of Synechococcus; hence this estimate is a minimum. In untreated seawater samples, lytic viral production was estimated to remove ca. 27% of the gross heterotrophic bacterial production, and a minimum of 1.0% of the gross cyanobacterial production. Our results demonstrate very high levels of lysogeny in the heterotrophic bacterial community, outside of an oligotrophic environment, and the presence of inducible lysogens in Synechococcus spp. during a naturally occurring bloom. These data emphasize the need for further examination of the factors influencing lytic and lysogenic viral infection in natural microbial communities. [TOP OF PAGE]
Marine phage genomics. Paul,J.H., Sullivan,M.B., Segall,A.M., Rohwer,F. (2002). Comparative Biochemistry and Physiology 133:463-476. Marine phages are the most abundant biological entities in the oceans. They play important roles in carbon cycling through marine food webs, gene transfer by transduction and conversion of hosts by lysogeny. The handful of marine phage genomes that have been sequenced to date, along with prophages in marine bacterial genomes, and partial sequencing of uncultivated phages are yielding glimpses of the tremendous diversity and physiological potential of the marine phage community. Common gene modules in diverse phages are providing the information necessary to make evolutionary comparisons. Finally, deciphering phage genomes is providing clues about the adaptive response of phages and their hosts to environmental cues. [TOP OF PAGE]
[Physical mapping of DNA of cyanophage LPP-3]. Syrchin,S.A., Mendzhul,M.I. (2002). Mikrobiol. Zh. 64:24-30. Restrictases fit for the purposes of physical mapping of cyanophage LPP-3 DNA have been selected as a result of the restriction analysis. The use of the methods of mutual hydrolysis, restriction of the fragment isolated from gel and terminal labeling allowed formation a physical map of LPP-3 cyanophage DNA with the complete scheme of allocation of 14 sites for 8 restrictases: Alw44I, Bsp1191, BsuRI, Eco147I, EheI, NcoI, Kpn2I and PvuI as well as the position of certain sites for restrictases HindIII, KpnI and Sau3A. [TOP OF PAGE]
[Some peculiarities of DNA structure of cyanophage LPP-3]. Syrchin,S.A., Mendzhul,M.I. (2002). Mikrobiol. Zh. 64:35-43. The efficiency of radioactive labeling of 3'- and 5'-ends of cyanophage LPP-3 DNA by polynucleotide kinase T4 and terminal transferase under various reaction conditions has been investigated. The obtained data prove that cyanophage LPP-3 DNA has the protruding 3'-ends. The experiments on ligation of native molecules of LPP-3 DNA evidence that the virus genome ends do not display any complimentarity. Separate fragments of LPP-3 DNA were cloned. The restriction analysis of the cloned fragments has confirmed a supposition on the absence of LPP-3 cyanophage of GGGCC and GGCCC sequences in the genome. A hypothesis has been suggested about similar site-specificity of the virus. Counterselection of the genome LPP-3 cyanophage allows it to be considered a promising one in the construction of new cloning vectors in cyanobacterium. [TOP OF PAGE]
Phylogenetic diversity of marine cyanophage isolates and natural virus communities as revealed by sequences of viral capsid assembly protein gene g20. Zhong,Y., Chen,F., Wilhelm,S.W., Poorvin,L., Hodson,R.E. (2002). Appl. Environ. Microbiol. 68:1576-1584. In order to characterize the genetic diversity and phylogenetic affiliations of marine cyanophage isolates and natural cyanophage assemblages, oligonucleotide primers CPS1 and CPS8 were designed to specifically amplify ca. 592-bp fragments of the gene for viral capsid assembly protein g20. Phylogenetic analysis of isolated cyanophages revealed that the marine cyanophages were highly diverse yet more closely related to each other than to enteric coliphage T4. Genetically related marine cyanophage isolates were widely distributed without significant geographic segregation (i.e., no correlation between genetic variation and geographic distance). Cloning and sequencing analysis of six natural virus concentrates from estuarine and oligotrophic offshore environments revealed nine phylogenetic groups in a total of 114 different g20 homologs, with up to six clusters and 29 genotypes encountered in a single sample. The composition and structure of natural cyanophage communities in the estuary and open-ocean samples were different from each other, with unique phylogenetic clusters found for each environment. Changes in clonal diversity were also observed from the surface waters to the deep chlorophyll maximum layer in the open ocean. Only three clusters contained known cyanophage isolates, while the identities of the other six clusters remain unknown. Whether or not these unidentified groups are composed of bacteriophages that infect different Synechococcus groups or other closely related cyanobacteria remains to be determined. The high genetic diversity of marine cyanophage assemblages revealed by the g20 sequences suggests that marine viruses can potentially play important roles in regulating microbial genetic diversity. [TOP OF PAGE]
Distribution of virus-like particles in an oligotrophic marine environment (Alboran Sea, Western Mediterranean). Alonso,M.C., Jimenez-Gomez,F., Rodriguez,J., Borrego,J.J. (2001). Microb. Ecol. 42:407-415. Viruses are abundant in a variety of aquatic environments, often exceeding bacterial abundance by one order of magnitude. In the present study, the spatial distribution of viruses in offshore waters of the Alboran Sea (Western Mediterranean) have been studied to determine the relationships between viruses and host communities in this oligotrophic marine environment. Viral abundance was determined using two methods: (i) epifluorescence light microscopy using the dsDNA binding fluorochrome DAPI, and (ii) direct counts by transmission electron microscopy (TEM). The results obtained were significantly different; the highest viral counts were obtained by mean of TEM analyses. In all the samples tested the number of viruses was exceeded by the bacterial concentrations, with a ratio between viral and bacterial titers varying between 1.4 and 20. VLP (virus-like particle) counts were not significantly correlated (p>0.001) with chlorophyll a concentration or the abundance of cyanobacteria. However, there was a positive and significant correlation with bacterial abundance (p<0.001). The analysis of size and morphology of viral particles by TEM and the correlation obtained between the numbers of VLP and bacteria suggest that the majority of the viral particles in the Alboran Sea are bacteriophages. None of the indirect evidence suggested that eukaryotic algae or cyanobacteria were important host organisms in these waters. [TOP OF PAGE]
Use of octyl beta-thioglucopyranoside in two-dimensional crystallization of membrane proteins. Chami,M., Pehau-Arnaudet,G., Lambert,O., Ranck,J.L., Levy,D., Rigaud,J.L. (2001). J Struct Biol 133:64-74. A great interest exists in producing and/or improving two-dimensional (2D) crystals of membrane proteins amenable to structural analysis by electron crystallography. Here we report on the use of the detergent n-octyl beta-d-thioglucopyranoside in 2D crystallization trials of membrane proteins with radically different structures including FhuA from the outer membrane of Escherichia coli, light-harvesting complex II from Rubrivivax gelatinosus, and Photosystem I from cyanobacterium Synechococcus sp. We have analyzed by electron microscopy the structures reconstituted after detergent removal from lipid-detergent or lipid-protein-detergent micellar solutions containing either only n-octyl beta-d-thioglucopyranoside or n-octyl beta-d-thioglucopyranoside in combination with other detergents commonly used in membrane protein biochemistry. This allowed the definition of experimental conditions in which the use of n-octyl beta-d-thioglucopyranoside could induce a considerable increase in the size of reconstituted membrane structures, up to several micrometers. An other important feature was that, in addition to reconstitution of membrane proteins into large bilayered structures, this thioglycosylated detergent also was revealed to be efficient in crystallization trials, allowing the proteins to be analyzed in large coherent two-dimensional arrays. Thus, inclusion of n-octyl beta-d-thioglucopyranoside in 2D crystallization trials appears to be a promising method for the production of large and coherent 2D crystals that will be valuable for structural analysis by electron crystallography and atomic force microscopy. [TOP OF PAGE]
A conserved genetic module that encodes the major virion components in both the coliphage T4 and the marine cyanophage S-PM2. Hambly,E., Tétart,F., Desplats,C., Wilson,W.H., Krisch,H.M., Mann,N.H. (2001). Proc. Natl. Acad. Sci. USA 98:11411-11416. Sequence analysis of a 10-kb region of the genome of the marine cyanomyovirus S-PM2 reveals a homology to coliphage T4 that extends as a contiguous block from gene (g)18 to g23. The order of the S-PM2 genes in this region is similar to that of T4, but there are insertions and deletions of small ORFs of unknown function. In T4, g18 codes for the tail sheath, g19, the tail tube, g20, the head portal protein, g21, the prohead core protein, g22, a scaffolding protein, and g23, the major capsid protein. Thus, the entire module that determines the structural components of the phage head and contractile tail is conserved between T4 and this cyanophage. The significant differences in the morphology of these phages must reflect the considerable divergence of the amino acid sequence of their homologous virion proteins, which uniformly exceeds 50%. We suggest that their enormous diversity in the sea could be a result of genetic shuffling between disparate phages mediated by such commonly shared modules. These conserved sequences could facilitate genetic exchange by providing partially homologous substrates for recombination between otherwise divergent phage genomes. Such a mechanism would thus expand the pool of phage genes accessible by recombination to all those phages that share common modules. [TOP OF PAGE]
Distribution, isolation, host specificity, and diversity of cyanophages infecting marine Synechococcus spp. in river estuaries. Lu,J., Chen,F., Hodson,R.E. (2001). Appl. Environ. Microbiol. 67:3285-3290. The abundance of cyanophages infecting marine Synechococcus spp. increased with increasing salinity in three Georgia coastal rivers. About 80% of the cyanophage isolates were cyanomyoviruses. High cross-infectivity was found among the cyanophages infecting phycoerythrin-containing Synechococcus strains. Cyanophages in the river estuaries were diverse in terms of their morphotypes and genotypes. [TOP OF PAGE]
Fingerprinting viral assemblages by pulsed field gel electrophoresis. Steward,G.F. (2001). pp. 85-102. In In Paul,J.H. (ed.), Marine Microbiology. Academic Press, London. Viruses are the most abundant microorganisms in marine and freshwater environments and perhaps the most genetically diverse (Fuhrman and Suttle, 1993). Counting viruses in aquatic samples is now a routine matter, but assessing the diversity and dynamics within complex assemblages is still a challenge. DNA-based fingerprinting approaches which rely on amplification of rRNA gene fragments by PCR have facilitated analyses of bacterial community composition. These approaches have more restricted application when analyzing viral assemblages, because of the extreme genetic diversity among viruses. Unlike in bacteria, there are no gene sequences conserved in all viruses which can serve as universal primer sites for PCR amplification. PCR-based analyses of viral assemblages must therefore target specific subsets of the total viral assemblage. For example, PCR amplification of specific genes has recently been used to examine the genetic diversity among cyanophages (Fuller et al., 1998) and among phycodnaviridae (Chen et al., 1996; Short and Suttle, 1999). A more general fingerprinting approach, which encompasses the total viral assemblage, is a valuable complement to these more specific, higher resolution analyses. The approach described here uses variation in genome size as the basis for obtaining a fingerprint of a viral assemblage (Klieve and Swain, 1993). A whole genome fingerprinting approach is possible, because viral genomes can vary greatly in length (a few thousand to hundreds of thousands of base pairs) yet they fall within a range that is easily resolved using pulsed field gel electrophoresis (PFGE). The PFGE fingerprinting technique provides a quick and relatively simple means of visualizing differences in the composition of viral assemblages (Swain et al., 1996; Wommack et al., 1999a; Steward and Azam, 2000). As a supplement to the more specific treatment of PFGE provided in this chapter, the reader is encouraged to consult the excellent introductory text to PFGE by Birren and Lai (1993). [TOP OF PAGE]
Genomic sequence of a lytic cyanophage of Synechococcus spp. Lu,J.R., Chen,F., Hodson,R.E. (2000). Abstracts of the General Meeting of the American Society for Microbiology 100, 465. [TOP OF PAGE]
Ecology of bacteriophages in nature. Paul,J.H., Kellogg,C.A. (2000). pp. 211-246. In In Hurst,C.J. (ed.), Viral Ecology. Academic Press, San Diego. [first paragraph] The role of bacteriophages (viruses that infect bacteria) in the environment has been the subject of intense investigation over the past several years. The development of techniques to study natural viral populations in situ has progressed tremendously. Various aspects of bacteriophage ecology in nature - including abundance, role in microbial mortality and water column trophodynamics, viral decay rates, repair mechanisms, and lysogeny - are now becoming or are nearly understood. However, most of these studies have been performed in aquatic environments. Thus, this review will mainly be limited to a discussion of aquatic environments. For reviews of the earlier literature, the reader is referred to Moebus (1987), Goyal et a2. (1987), Fuhrman and Suttle (1993), Ackermann and DuBow (1987), and Proctor (1997). [TOP OF PAGE]
Cyanophages and their role in the ecology of cyanobacteria. Suttle,C.A. (2000). pp. 563-589. In In Whitton,B.A. and Potts,M. (eds.), The Ecology of Cyanobacteria: Their Diversity in Time and Space. Kluwer Academic Publishers, Boston. Cyanophages belong to three recognized families of double-stranded DNA viruses; Myovirida (contractile tails); Styloviridae (long non-contractile tails); and Podoviridae (short tails). They have a complex pattern of host ranges, are widely distributed, and can be readily isolated from marine and fresh waters. Although cyanophages are related to other bacteriophages, it is likely that they evolved more than 3 billion years ago when cyanobacteria diverged from other prokaryotes. In marine waters, genetically-diverse Myoviridae which infected Synechococcus spp. are the most abundant cyanophages; Styloviridae and Podoviridae are most commonly isolated from fresh waters. Morphological evidence also suggests that freshwater and marine myoviruses are more closely related to each other than they are to other bacteriophages. Cyanophages that infect phycoerythrin-rich Synechococcus spp. can be extremely abundant in coastal marine environments where they can occur at titers in excess of 10[6] mL[-1] and 10[5] g[-1] of sediment. In surface waters abundance varies over orders of magnitude on a seasonal basis. Abundance follows that of Synechococcus, with evidence for a threshold in Synechococcus of ca. 10[3] to 10[4] mL[-1] beyond which cyanophage abundance increases greatly. In nearshore waters the high concentrations of cyanophages and Synecoccus result in high encounter frequencies and selection for Synecoccus communities that are largely resistant to infection. Encounters are much less frequent offshore and this leads to the appearance of a community that appears to have low resistance to infection. In freshwaters, viruses which infect filamentous cyanobacteria appear to be most abundant and also show strong seasonal dynamics however; even in the most eutrophic environments titers are orders of magnitude less than in productive coastal waters. Little effort was made to screen freshwaters for cyanophages that infect phycoerythrin-rich Synechococcus. In marine surface waters turnover times for cyanophage populations range from hours to days. Solar radiation has a major effect on cyanophage infectivity and results in the selection of cyanophage communities that are more resistant to destruction by sunlight during summer. In constrast to surface waters, infectious cyanophages can persist in sediments for at least 100 years. Although the effect of cyanophages on the mortality of cyanobacterial communities is likely to be variable, current estimates suggest that cyanophages are responsible for the removal of approximately 3% of marine Synechococcus on a daily basis. In addition to the lytic infection, lysogenic associations were clearly demonstrated in filamentous and unicellular cyanobacteria, but the ecological implications of lysogeny remain unexplored. Environmental factors and the physiological state of cyanobacteria clearly affect cyanophage-cyanobacterial interactions but remain poorly understood. [TOP OF PAGE]
The ecology, evolutionary and geochemical consequences of viral infection of cyanobacteria and eukaryotic algae. Suttle,C.A. (2000). pp. 248-286. In In Hurst,C.J. (ed.), Viral Ecology. Academic Press, New York. [first paragraph] More than 35 years ago, Safferman and Morris (1963) reported the isolation of a virus (cyanophage) that infected a freshwater filamentous “blue-green alga.” This discovery stimulated research that led to isolation of many viruses that infect freshwater cyanobacteria. Although the potential for viruses to control cyanobacterial blooms was recognized (Safferman and Morris, 1964; Shilo, 1971), much of this work focused on the biology rather than the ecology of cyanophages (reviewed in Brown, 1972; Padan and Shilo, 1973; Safferman, 1973; Stewart and Daft, 1977; Sherman and Brown, 1978; Martin and Benson, 1988). At about the same time, evidence for viral infection of eukaryotic algae was beginning to emerge with reports by Zavarzina (1961, 1964) of lysis of Chlorella pyrenoidosa cultures. However, it was not until a decade later that observations of viruslike particles (VLPs) in eukaryotic algae began to appear in the literature (e.g., Lee, 1971; Chapman and Lang, 1973; Lemke, 1976; Dodds, 1979, 1983), and shortly thereafter a virus (CCV) was isolated that infected the macroalga Cham corullina (Gibbs et al., 1975; Skotnicki et al., 1976). This was followed a few years later by isolation of a virus (MPV) that infected the marine photosynthetic flagellate Micromonas pusilla (Mayer, 1978; Mayer and Taylor, 1979). Despite the ecological implications of viruses infecting major primary producers in aquatic environments, interest in viruses that infect eukaryotic algae was slow to gather. In fact, after the work by Waters and Chan (1982), there was little further interest in MPV, and the virus was lost from culture (F. J. R. Taylor, personal communication). Furthermore, by the 1980s ecological interest in cyanophages also began to wane as cyanobacterial blooms were brought under control by regulations reducing nutrient inputs to lakes. The decline in interest was exacerbated by the lack of appreciation by many algal and aquatic ecologists of the ecological importance of microbes in general and of viruses in particular. Although there was little interest in the ecological aspects, there were major advances in our understanding of the biology of a group of viruses that infect Chlorella-like algae that are symbionts of Hydra viridis and Paramecium bursaria. These viruses were isolated in the early 1980s and possess a number of unusual features (reviewed in Van Etten et al., 1991; Reisser, 1993; Van Etten, 1995; Van Etten and Meints, 1999) that led to the creation of a new family of viruses, Phycodnaviridae (Van Etten and Ghabrial, 1991). As well, work has progressed on a group of widely distributed viruses that infect filamentous brown algae belonging to order Ectocarpales (Oliveira and Bisalputra, 1978; Muller, 1991; Henry and Meints, 1992; Muller and Frenzer, 1993; Muller, 1996; Van Etten and Meints, 1999). [TOP OF PAGE]
Transmission electron microscope analysis of viruses in the freshwater lakes of Signy Island, Antarctica. Wilson,W.H., Lane,D., Pearce,D., Ellis-Evans,J.C. (2000). Polar Biology 23:657-660. [TOP OF PAGE]
Seasonal changes in densities of cyanophage infectious to Microcystis aeruginosa in a hypereutrophic pond. Manage,P., Kawabata,Z., Nakano,S. (1999). Hydrobiologia. 411:211-216. Seasonal changes in densities of cyanophages infectious to Microcystis aeruginosa were studied in a hypereutrophic pond from March 1997 to January 1998 to elucidate the potential impact of the cyanophage on M. aeruginosa mortality. Densities of M. aeruginosa ranged between 1.8 X 10⁴ and 9.4 X 10⁵ cells ml-1, while those of the cyanophages were between 2.0 X 10² and 4.2 X 10⁴ PFU ml^-1. Sharp decreases in densities of M. aeruginosa were detected on 10 June and 24 September, as densities of the cyanophages increased, suggesting release of the cyanophages due to the lysis of infected M. aeruginosa. Thus, infection by cyanophages may have a substantial effect on cyanobacterial succession in the pond. Densities of cyanophages became undetectable when those of M. aeruginosa were at low levels during winter. We suggest that there is a tight host-pathogen relationship between M. aeruginosa and the cyanophage in the pond. [TOP OF PAGE]
Cyanophages. Martin,E.L., Kokjohn,T.A. (1999). pp. 324-332. In In Granoff,A. and Webster,R.G. (eds.), Encyclopedia of Virology second edition. Academic Press, San Diego. The cyanobacteria with their prokaryotic structure and oxygenic photosynthesis occupy a unique position among living organisms. These characteristics closely relate them not only to the eubacteria, but also to eucaryotic algae and plants. Over the last 5 or 6 years research has continued to investigate the genetics, physiology, and metabolism, primarily for cyanophages which replicate in both unicellular and filamentous freshwater cyanobacteria; however, the major impetus of the latest research has shifted to the role cyanophages occupy in marine ecosystems. Cyanophages are of critical importance in that they can cause substantial lysis of primary producer organisms. This in turn can exert an extensive effect on the dynamics of carbon flow in many of the marine environments studied. It is hoped that many of the aspects of the research described here can continue to come together to give a more interconnected and complete understanding of the interactions between cyanophages and cyanobacteria. [TOP OF PAGE]
First report of a putative cyanophage, MC-1 of Microcoleus sp. Rosowski,J.R., Shaffer,J.J., Martin,E.L. (1999). Microsc. Microanalysis 5:1142-1143. [TOP OF PAGE]
Phycodnaviridae. van Etten,J.L. (1999). pp. 183-193. In AnonymousVirus Taxonomy - Seventh Report. [TOP OF PAGE]
Changes in bacterial and eukaryotic community structure after mass lysis of filamentous cyanobacteria associated with viruses. van Hannen,E.J., Zwart,G., van Agterveld,M.P., Gons,H.J., Ebert,J., Laanbroek,H.J. (1999). Appl. Environ. Microbiol. 65:795-801. During an experiment in two laboratory-scale enclosures filled with lake water (130 liters each) we noticed the almost-complete lysis of the cyanobacterial population. Based on electron microscopic observations of viral particles inside cyanobacterial filaments and counts of virus-like particles, we concluded that a viral lysis of the filamentous cyanobacteria had taken place. Denaturing gradient gel electrophoresis (DGGE) of 16S ribosomal DNA fragments qualitatively monitored the removal of the cyanobacterial species from the community and the appearance of newly emerging bacterial species. The majority of these bacteria were related to the Cytophagales and actinomycetes, bacterial divisions known to contain species capable of degrading complex organic molecules. A few days after the cyanobacteria started to lyse, a rotifer species became dominant in the DGGE profile of the eukaryotic community. Since rotifers play an important role in the carbon transfer between the microbial loop and higher trophic levels, these observations confirm the role of viruses in channeling carbon through food webs. Multidimensional scaling analysis of the DGGE profiles showed large changes in the structures of both the bacterial and eukaryotic communities at the time of lysis. These changes were remarkably similar in the two enclosures, indicating that such community structure changes are not random but occur according to a fixed pattern. Our findings strongly support the idea that viruses can structure microbial communities. [TOP OF PAGE]
Sunlight-induced DNA damage and resistance in natural viral communities. Weinbauer,M.G., Wilhelm,S.W., Suttle,C.A., Pledger,R.J., Mitchell,D.L. (1999). Aquat. Microb. Ecol. 17:111-120. Using a highly specific radioimmunoassay, the sunlight-induced formation of cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts ([6-4] PPs) in viral DNA was investigated for natural virus communities in offshore and coastal waters of the western Gulf of Mexico as well as for clonal viral isolates. Concentrations of (6-4) PPs were consistently lower than CPD concentrations, and ranged from 1.5 to 17.0% of total measured photodamage. The accumulation of photoproducts varied among the natural viral community, the marine Vibrio phage PWH3a-P1 and the Synechococcus sp. DC2 (WH7803) cyanophage SYN-M3, which were deployed in situ from dawn until dark. Natural viral communities were more resistant to DNA damage than the cyanophage isolate SYN-M3, which was more resistant to damage than bacteriophage PWH3a-P1. Moreover, depth profiles revealed that photodamage in viral isolates deployed in the water column accumulated more rapidly at offshore stations than at coastal stations. In natural virus communities collected from offshore surface waters, photodamage accumulated during the solar day with maximum damage occurring between 15:00 and 18:00 h. Depth profiles obtained during calm seas showed that photodamage concentrations were high in surface waters at the offshore stations and at 1 coastal station. Results at other coastal stations undergoing significant mixing demonstrated no photoproduct accumulations. Results demonstrate that natural virus communities were more tolerant to DNA damaging radiation than the laboratory isolates used in this study. Consequently, laboratory isolates can be poor proxies for UV impacts on natural viral communities. [TOP OF PAGE]
Analysis of cyanophage diversity and population structure in a south-north transect of the Atlantic ocean. Wilson,W., Fuller,N., Joint,I., Mann,N. (1999). Bull. Inst. Océanogr. Manaco 19:209-216. [TOP OF PAGE]
Analysis of cyanophage diversity and population structure in a south-north transect of the Atlantic ocean. Wilson,W.H., Fuller,N.J., Joint,I.R., Mann,N.H. (1999). Bull. Inst. Océanogr. Manaco 0:209-216. Cyanophages (viruses which infect cyanobacteria) are abundant in the marine environment and are thought to be a significant factor in determining the dynamics of Synechococcus spp. populations. In an effort to use molecular techniques to characterise cyanophage populations, we designed cyanophage-specific (CPS) PCR primers based on a gene found in three genetically distinct marine cyanophages (Fuller et al., 1998). CPS primers were used to amplify cyanophage DNA extracted from viral communities concentrated from sea-water samples obtained during a cruise transect between the Falkland Islands, in the south Atlantic ocean, to the UK. Following phylogenetic analysis of cloned and sequenced PCR products, it was revealed that genetic diversity of marine cyanophage clones within a single water sample was as great as clones and cyanophage isolates collected between different oceans. Denaturing gradient gel electrophoresis (DGGE) analysis confirmed this high diversity. DGGE analysis also revealed changes in cyanophage population structure in surface seawater over the south-north transect and throughout depth profiles in the water column. Maximum Synechococcus spp. concentrations, in a stratified water column, correlated with maximum cyanophage diversity. [TOP OF PAGE]
Blue-green algal viruses (cyanophages). Zhao,Y., Shi,Z., Huang,G., Wang,X. (1999). Virologica Sinica 14:100-105. [TOP OF PAGE]
Dissolved esterase activity as a tracer of physoplankton lysis: Evidence of high phytoplankton lysis rates in the northwestern Mediteranean. Agustí,S., Satta,M.P., Mura,M.P., Benavent,E. (1998). Limnol. Oceanogr. 43:1836-1849. Phytoplankton cell lysis is perceived to be an important loss process in the sea, although a quantification of this process has proved elusive. A recently developed method, based on the measurement of dissolved esterase activity (EA), was used to estimate the release of esterases following phytoplankton cell lysis in an effort to evaluate the importance of this process as a loss factor in the summer phytoplankton of the northwestern Mediterranean Sea. Implicit in this method was the assumption that only the lysis of phytoplankton cells caused these enzymes to be released to the medium. This assumption was tested by analyzing the presence and release of esterases by marine bacteria, heterotrophic flagellates, and heterotrophic ciliates, all isolated from the Blanes Bay (northwestern Mediterranean, Spain), and by phytoplankton grown in culture (Synechococcus elongatus, Dunaliella sp., Chlorella sp., Phaeodactyllum tricornutum, and Chaetoceros decipiens). The dissolved EA found during the growth, stationary, and decay phases of microheterotrophs (bacteria, flagellate, and ciliate) was negligible when compared to that found for phytoplanktonic cultures. Differences in cell volume explained the differences in cell EA among the organisms, but heterotrophs showed lower cell EA (10-50-fold) than phytoplanktonic cells of similar cell size. These results support the assumption that microheterotrophs do not contribute significant amounts of EA to the dissolved pear, allowing the use of the method to estimate phytoplankton lysis. Independent estimates of cell, loss in phytoplankton cultures, derived from cell cycle analysis, confirmed the estimates of cell lysis obtained from the measurement of dissolved EA.

During the study conducted in the Mediterranean Sea, the water column was strongly stratified, showing a deep (40-55 m) chlorophyll a (Chl a) maximum (DCM; 1.25 +/- 0.09 mu g liter^-1) and low surface Chl a concentrations (0.09 +/- 0.008 mu g liter(-1)). Phytoplankton lysis rates ranged between 0.026 d^-1 and 1.9 d^-1, and they declined significantly with depth; the fastest rates were found in surface waters and the slowest ones at the DCM. Despite the fast gross growth rates of surface phytoplankton las calculated from phytoplankton biovolume and oxygen production), the calculated lysis rates represented a considerable proportion of gross phytoplankton growth rate (50%) at the surface, whereas they were comparatively less important at the DCM (7%). These results provide strong evidence that phytoplankton lysis can be an important loss factor in the surface waters of this stratified, oligotrophic sea. Phytoplankton lysis could provide the loss factor needed to explain the low phytoplankton biomass despite fast growth and low grazing rates in the northwestern Mediterranean surface waters. The high lysis rate of phytoplankton in surface waters represents an important path by which primary production may fuel the growth of microheterophic organisms, consistent with the high respiration rate of the surface community examined. The conclusion that phytoplankton lysis rates can occur at rates high enough to influence food web dynamics and biogeochemical cycles in the oligotrophic ocean should stimulate research on this largely neglected loss factor in phytoplankton ecology. [TOP OF PAGE]
Occurrence of a sequence in marine cyanophages similar to that of T4 gp20 and its application to PCR-based detection and quantification techniques. Fuller,N.J., Wilson,W.H., Joint,I.R., Mann,N.H. (1998). Appl. Environ. Microbiol. 64:2051-2060. Viruses are ubiquitous components of marine ecosystems and are known to infect unicellular phycoerythrin-containing cyanobacteria belonging to the genus Synechococcus. A conserved region from cyanophage genome was identified in three genetically distinct cyanomyoviruses, and a sequence analysis revealed that this region exhibited significant similarity to a gene encoding a capsid assembly protein (gp20) from the enteric coliphage T4. The results of a comparison of gene 20 sequences from three cyanomyoviruses and T4 allowed us to design two degenerate PCR primers, CPS1 and CPS2, which specifically amplified a 165-bp region from the majority of cyanomyoviruses tested. A competitive PCR (cPCR) analysis revealed that cyanomyovirus strains should be accurately enumerated, and it was demonstrated that quantification was log-linear over ca. 3 orders of magnitude. Different calibration curves were obtained for each of the three cyanomyovirus strains tested; consequently, cPCR performed with primers CPS1 and CPS2 could lead to substantial inaccuracies in estimates of phage abundance in natural assemblages. Further sequence analysis of cyanomyovirus gene 20 homologs would be necessary in order to design primers which do not exhibit phage-to-phage variability in priming efficiency. It was demonstrated that PCR products of the correct size could be amplified from seawater samples following 100x concentration and even directly without any prior concentration. Hence, the use of degenerate primers in PCR analysis of cyanophage populations should provide valuable data on the diversity of cyanophages in natural assemblages. Further optimization of procedures may ultimately lead to a sensitive assay which can be used to analyze natural cyanophage populations both quantitatively (by cPCR) and qualitatively following phylogenetic analysis of amplified products. [TOP OF PAGE]
The effect of cyanophages on the morality of Synechococcus spp. and selection for UV resistant viral communities. Garza,D.R., Suttle,C.A. (1998). Microb. Ecol. 36:281-292. Viruses that cause lysis of Synechococcus spp. are present throughout the year in the western Gulf of Mexico. The effect of sunlight on loss rates of cyanophage infectivity was determined by incubating natural cyanophage communities and cyanophage isolates (strains S-PWM1 and S-PWM3) in UV-transparent bags at the surface, and at depth, on several occasions throughout the year. Decay rates of infectivity of natural cyanophage communities at the surface, at Port Aransas, Texas, USA, ranged from undetectable to 0.335 h(-1), with the highest rates occurring during the summer. During the spring and winter, decay rates of cyanophage isolates and natural cyanophage communities were generally similar, but during summer, decay rates of isolates were as much as twofold higher than the natural communities. In situ incubations at two offshore stations during a bloom of Synechococcus spp. produced decay rates of 0.53 and 0.75 d(-1), integrated over the mixed layer and averaged over 24 h. Based on a burst size of 81 viruses produced per lysed cell (measured for natural cyanobacterial communities in the Gulf of Mexico), cyanophages imposed mortality rates of 1 and 8%, respectively, on Synechococcus spp. In contrast, in nearshore incubations in the winter and spring, cyanophages were responsible for removing <1% of the Synechococcus cells on a daily basis. Only an estimated 2 to 3% of contacts led to viral infections (based on theoretical contact rates between host cells and cyanophages, and estimates of cyanophage mortality), regardless of the time of year or concentrations of viruses and hosts. These results indicate that natural cyanophage communities tolerate damage by solar radiation better in summer than in winter. Moreover, net decay rates of cyanophage infectivity in sunlight were similar, whether host cells were present or not, indicating that detectable cyanophage production did not occur during daytime in situ incubations. [TOP OF PAGE]
[Key enzymes of biosynthesis of amino acids of the glutamic series in the virus-cell system Anabaena variabilis + A-1]. Mendzhul,M.I., Lysenko,T.G., Koltukova,N.V. (1998). Ukr Biokhim Zh 70:16-22. The influence of cyanophage A-1 reproduction on glutamate dehydrogenase (GDG) and glutamine synthetase (GS) in A. variabilis cells was studied. It was determined that the both enzymes are intensified by 70% and 30%, accordingly. Isoenzymes of GDG and GS were isolated from native and infected cells of cyanobacteria, they had various physicochemical properties. It is concluded that cyanophage development causes the specific modification of cell enzymes. [TOP OF PAGE]
Principles of virus-directed regulation of formation of the dynamic system virus-cell (problems, methodology and prospects of cyanophagia). Mendzhul,M.I., Lysenko,T.G., Koltukova,N.V., Syrchin,S.A., Sukhanov,S.N. (1998). Mikrobiol. Zh. 60:66-78. Dynamics of virus-directed regulation of formation of the complex virus - cell has been studied on the example of the system cyanophage-cyanobacterium. It is shown that in the process of virus reproduction the host-cell loses its own genetic apparatus, system of regulation of biosynthetic processes, reproductive ability and other functions of vital importance. As a matter of fact the formed virus - cell complex turns into powerful generator of nucleotides and amino acids for nonlimited synthesis of virus nucleic acids, proteins and morphogenesis of virions. The question is discussed concerning the possibility of the use of the system cyanophage cyanobacterium as the experimental models for development of functional unified model of productive infection, effective methods of prophylaxis and therapy of virus infections as well as the decision of various biotechnological problems. [TOP OF PAGE]
The role of sunlight in the removal and repair of viruses in the sea. Wilhelm,S.W., Weinbauer,M.G., Suttle,C.A., Jeffrey,W.H. (1998). Limnol. Oceanogr. 43:586-592. We investigated the in situ destruction rates of marine viral particles as well as the decay rates of infectivity for viral isolates along an similar to 400-km transect from oligotrophic offshore waters to productive coastal waters in the Gulf of Mexico. Light-mediated decay rates of viral infectivity averaged over the solar day ranged from 0.7 to 0.85 h super(-1) in surface waters at all stations and decreased with depth in proportion to the attenuation of UVB (305 nm). The destruction rates of viral particles also decreased with depth, although the rates of particle destruction were only 22-61% of infectivity when integrated over the mixed layer. The rates of viral particle destruction indicated that at three of four stations 6-12% of the daily bacterial production would have to be lysed in order to maintain ambient viral concentrations. At the fourth station, where there was a dense bloom of Synechococcus spp. and the mixed layer was shallower, 34-52% of the daily bacterial production would have to be lysed. A comparison of the difference between destruction rates of viral particles and infectivity integrated over the depth of the mixed layer implies that host-mediated repair must have restored infectivity to 39-78% of the sunlight-damaged viruses daily. The calculated frequency of contacts between viral particles and bacterial cells that resulted in infection (contact success) ranged from similar to 18 to 34% in offshore waters, where the frequency of contacts between viruses and bacteria was much lower, to similar to 1.0% at the most inshore station, where contact rates are much higher. This suggests that in offshore waters bacterial communities are less diverse, and that there is less selection to be resistant to viral infection. This paper provides a framework for balancing viral production, destruction, and light-dependent repair in aquatic viral communities. [TOP OF PAGE]
Population dynamics of phytoplankton and viruses in a phosphate-limited mesocosm and their effect on DMSP and DMS production. Wilson,W.H., Turner,S., Mann,N.H. (1998). Estuarine, Coastal and Shelf Science 46:49-59. The effect of phosphate limitation on viral abundance, phytoplankton bloom dynamics and production of dimethylsulphoniopropionate (DMSP) and dimethyl sulphide (DMS) was investigated in seawater mesocosm enclosures, in a Norwegian fjord, during June 1995. Daily estimates of viral concentrations, based on transmission electron microscope (TEM) counts, varied on an apparently random basis in each of the enclosures. A large Synechococcus spp. bloom developed in an enclosure which was maintained at a high N:P ratio, simulating phosphate-deplete growth conditions. Following phosphate addition to this enclosure, there was a large increase in estimated virus numbers shortly before an apparent collapse of the Synechococcus bloom. It is tentatively suggested that lysogenic viruses were induced following phosphate addition to the phosphate-limited enclosures, and that these observations add to a growing body of evidence which supports the hypothesis that nutrient availability may be responsible for the switch between lysogeny and lytic production. High DMS concentrations and viral numbers were observed on the demise of the flagellate (predominantly Emiliania huxleyi) and diatom blooms, but overall there was no significant correlation. Highest concentrations of DMSP were associated with blooms of E. huxleyi, for which an intracellular concentration of 0.5 pg cell^-1 (SD, 0.06) was calculated. Good correlation of DMSP with Synechococcus spp. cell numbers was observed, suggesting that these species of picoplankton may be significant producers of DMSP. No effects of phosphate limitation on DMS and/or DMSP production were evident from the data. [TOP OF PAGE]
Growth and phage resistance of Anabaena sp. strain PCC 7120 in the presence of cyanophage AN-15. Mole,R., Meredith,D., Adams,D.G. (1997). Journal of Applied Phycology [J. Appl. Phycol. ] 9:339-345. The cyanophage AN-15 was found to have a requirement for either 1 mM calcium or 1 mM magnesium ions to maintain viral stability, whereas 1 mM calcium ions alone were essential for the infection process to proceed in Anabaena sp. strain PCC 7120. Following prolonged incubation, phage-resistant cells were detected at a high frequency (approximately 10 super(-5)) in lysates, as either renewed growth in liquid cultures, or as colonies in confluently lysed lawns. Southern hybridisation failed to detect AN-15 DNA in any of the resistant strains, implying that resistance is unlikely to be due to the presence of temperate phages. A high rate of spontaneous mutation is therefore likely to be the cause of resistance. Two classes of resistant cells were identified; those in which AN-15 failed to attach to host cells, and those in which attachment occurred, but subsequent replication was defective. However, it was possible to overcome phage resistance by the isolation of spontaneous mutants of AN-15, capable of infecting phage-resistant cells. These observations imply that if cyanophages are to be assessed as a means of controlling cyanobacterial blooms in freshwater bodies, the ionic (notably calcium) concentration of the water must be considered, together with the possible need to employ alternative cyanophage strains if resistance to the original one arises. [TOP OF PAGE]
Characterization of host-range mutants of cyanophage N-1. Sarma,T.A., Kaur,B. (1997). Acta Virol. 41:245-250. Fifteen host-range (h) mutants of cyanophage N-1 were characterized with reference to their efficiency of plating, time of appearance, morphology and size of plaques on Nostoc muscorum and its three phage-resistant (Nm 1/N-1, Nm 2/N-1 and Nm 8/N-1) mutants. While phage N-1 did not adsorb to the three phage-resistant mutants, the h mutants differed one from the other in having lower or higher adsorption rate constants on N. muscorum or the phage-resistant mutants. The inability of majority of h mutants isolated on Nm 1/N-1 to grow in Nm 8/N-1 was shown to be due to a failure of adsorption. The h mutants also differed one from the other in their reversion (back mutation) frequencies. The lethal doses (LD sub(37)) required to kill 37% of free phage particles after UV-irradiation, heating and ethylenediamine tetraacetate (EDTA) treatment greatly varied. Most of the h mutants were found to be considerably more sensitive to UV and thermic inactivation than N-1 while they were resistant to EDTA. The h mutants except five of them were unable to multiply at 40 degree C. The significance of these features is discussed. [TOP OF PAGE]
Viruses in aquatic ecosystems. A review. Sime-Ngando,T. (1997). Annee Biologique 36:181-210. Even though the contribution of water ecosystems for disseminating enteric viral pathogens has been known for decades, the importance of wild virions iii structuring aquatic communities and food webs has only come to light relatively recently. Evidences of viral infections in both pro-and eukaryotic phytoplankton, as well as in heterotrophic bacterio-and protozooplankton, have recently brought marine biologists to question the impact of viroplankton on processes such as (1) the mortality of microorganisms, (2) the nutrition of heterotrophic protists, (3) the promotion of genetic material exchanges among microbial populations, (4) the maintenance of species diversity, (5) the induction of planktonic aggregates, and (6) the cycling of organic matter in aquatic ecosystems. In this paper, all these points are reviewed and discussed, in the light of recent contributions to the ecology of aquatic viruses, for evidence of the impact of viruses on both steady and non-steady state processes in fresh- and salt-waters.

Viruses are ubiquitous, abundant and dynamic components of pelagic ecosystems. They are, undoubtedly, more diversified than the phage -like morphotypes that are generally characterized by the presence of an icosa- or octahedral head and a tail, via observations under electron microscope. The diversity of planktonic viruses is further enhanced from the genetic viewpoint, and likely implies the diversity of sensible hosts. Genetically related marine phages are likely widely distributed in the space (i. e. without significant geographical segregation), suggesting prevalence of a reduced competition among viral ''populations'', and that the main biotic limiting factor for a viral ''species'' production is the density of the sensible host. Some viral ''species'', known from marine systems, typically harbor knob-like projections and long spines (i. e. previously not noted from non.-aquatic habitats), which are suggested to increase the efficiency of hitting a specific host, especially in oligotrophic waters. Despite the general scarcity of viral isolates that lyse ciliated protozooplankton and metazoan zooplankton, it is becoming increasingly evident that most of the pelagic pro-and eukaryotic organisms are subject to infectious attacks from ambient ''free-living'' viruses.

Quantitatively, recent total counts from the plankton generally fall in between 10(4) and 10(8) viruses ml(-1), with seasonal high densities in spring and summer, and a lowering tendency in abundance from the coastal to the open marine systems, and from the surface to the depth waters, likely in relation to temperature and the organic matter load. it was recently shown that lytic infection, rather than induction of lysogeny, is responsible for the majority of bacteriophage production in the plankton, especially in the coastal marine and surface waters and during blooming events, where the threshold-product level of virus x bacteria numbers of greater than or equal to 10(12) for the start of a viral-lytic activity is generally achieved. Closed linear relationships have been reported between viroplankton dynamics and bacteria, algae and nutrients. Because of the preponderance of allochtonous organic matter and cyanobacterial cells in lakes as compared to oceanic systems, the virus-to-bacteria ratio in lakes are significantly higher than in marines systems, although there is little trend in the virus-to-bacteria ratio with increasing trophy, and despite the occurrence of more bacteria per unit chlorophyll in lake samples.

The functional impact of virions on the structure and metabolism of planktonic communities is more important than their quantitative importance, as viruses represent only a minor fraction of the total planktonic biomass. The viral-induced mortality of microbial communities in marine systems is estimated to represent about 30 and < 10 pour 100 of the mortality of bacterio- and phytoplankton, respectively. Based on one study, the contribution of viruses to bacterial mortality in lakes seems considerably lower than in marine systems. The greatest impact of viruses on aquatic communities is likely through hazardous (i.e. non-steady state) processes which are difficult to quantified, such as the promotion of genetic material exchanges among populations and the maintenance of species diversity. The lytic pressure from virulent viruses may act as a ''nonstop'' inductor of modifications in the genetic heritage of host-organisms, thereby increasing the potential of these hosts to share their habitat with homologous species, i.e. with similar nutritional requirements.

It has recently been shown that lysates resulting from phage infection can caused a significant increase in metabolic activity of noninfected bacterioplankton community, but the growth efficiency of these noninfected hosts decreased in the presence of viruses, likely because of the increase in bacterial energy demand associated with extracellular degradation of polymers that are prevalent in viral lysates. This seems to verify the hypothesis on a substantial contribution of the lytic activity from viruses, to the cycling of organic matter in aquatic systems. Viral lytic production may indeed (1) reduce the bacterial biomass contribution to the transfer of metabolic energy on to higher-order consumers, (2) result in an increase of bacterial secondary production in the absence of an increase in the ambient primary production, and (3) increase competition between bacterial exo- or ectoenzyme activity and the feeding activity of protozoa on high molecular weight polymers (including viruses), although ingestion of viruses by protists seems to be of less importance in the carbon flows through the microbial food web in pelagic systems.

However, almost all studies on the ecology of pelagic viruses are done during a limited period of year, mainly in marine waters situated in temperate zones. The data discussed in this paper are thus to be considered as preliminary data. Nevertheless, viruses undoubtedly influence to various degrees the biological processes in aquatic ecosystems. The quantitative assessment of their functional impact is thus required for incorporation into models that simulate flues of matter, nutrients and energy in aquatic systems. This task is to be include on the agenda of both marine and freshwater biologists, as a high priority concern for the near future. [TOP OF PAGE]
Induction of a temperate marine cyanophage by heavy metal. Sode,K., Oonari,R., Oozeki,M. (1997). J. Mar. Biotechnol. 5:178-180. The activity of a temperate marine cyanophage, ms-1, of Synechococcus sp. NKBG 042902, was induced by Cu²⁺. This induction was specific to Cu²⁺ and dependent upon Cu²⁺ concentration. Cr, Pb, Co, and Zn were not effective as inducers. These results suggested that Cu²⁺ is a significant inducer for lysogenic cyanobacterial cells and consequently will be a potential trigger for changes in the cyanobacterial population in the marine environment. [TOP OF PAGE]
Lipopolysaccharide dependence of cyanophage sensitivity and aerobic nitrogen fixation in Anabaena sp. strain PCC 7120. Xu,X., Khudyakov,I., Wolk,C.P. (1997). Journal of Bacteriology [J. BACTERIOL. ] 179:2884-2891. Fox super(-) mutants of Anabaena sp. strain PCC 7120 are unable to fix dinitrogen in the presence of oxygen. A fragment of the DNA of Anabaena sp. was cloned by complementation of a spontaneous Fox super(-), cyanophage-resistant mutant, R56, and characterized. Random insertion of transposon Tn5 delimited the complementing DNA to a 0.6-kb portion of the cloned fragment. Sequencing of this region and flanking DNA showed one complete open reading frame (ORF) similar to the gene rfbP (undecaprenyl-phosphate galactosephosphotransferase) and two partial ORFs similar to genes rfbD (GDP-D-mannose dehydratase) and rfbZ (first mannosyl transferase), all of which are active in the synthesis of the O antigen unit of the lipopolysaccharide (LPS) component of the outer membrane of gram-negative bacteria. In a transposon (Tn5-1087b)-induced, Fox super(-), cyanophage-resistant mutant, B14, the transposon was found within the same rfbP-like ORF. The three ORFs were insertionally inactivated with the omega cassette or with Tn5::omega. Only the insertions in the rfbZ- and rfbP-like ORFs led to resistance to cyanophages A-1(L) and A-4(L) and to a Fox super(-) phenotype. Electrophoretic analysis showed that interruption of the rfbZ- and rfbP-like ORFs resulted in a change in or loss of the characteristic pattern of the lengths of the LPS, whereas interruption of the rfbD-like ORF merely changed the distribution of the lengths of the LPS to one with a greater prevalence of low molecular weights. According to electron microscopy, interruption of the rfbP-like ORF may have led to aberrant deposition of the layers of the heterocyst envelope, resulting in increased leakage of oxygen into the heterocyst. The results suggest that modified LPS may prevent cyanophage infection of Anabaena sp. vegetative cells and the formation of a functional heterocyst envelope. [TOP OF PAGE]
The diversity of bacteria, eukaryotic cells and viruses in an oligotrophic lake. Corpe,W.A., Jensen,T.E. (1996). Applied Microbiology and Biotechnology 46:622-630. An in situ transmission electron microscopic study of biomass samples concentrated from oligotrophic lake water revealed a variety of virus-infected microbial cells and many free viruses and virus-like particles. The most abundant group of microorganisms in screened and filtered water-column samples were 2 mu-m or less in diameter, and included representatives of several oligotrophic genera, Prosthecomicrobium, Ancyclobacter, Caulobacter and Hyphomicrobium. Among the prokaryotic host cells, which included both heterotrophs and autotrophs, on the basis of electron microscope observations. approximately 17% were infected with bacteriophage or bore adherent phage particles on their surfaces. Several bacterial morphotypes were observed among the prokaryotic hosts. Water samples passed through a 20-mu-m Nitex screen allowed us to concentrate and examine the larger host cells as well, including several species of single-celled algae and two amoeba species. The infected algal cells included those Chlorella-like in appearance, photosynthetic flagellates and others that could not be positively identified. About one-third of the eukaryotic cells were infected by viruses that were larger (150-200 nm) and structurally more complex than bacteriophages (50-60 nm). None of the viruses have been isolated, but when 0.2 mu-m filtrate from a biomass sample was spotted onto lawns of four representative heterotrophs and a Chlorella, the clearing observed was taken as evidence of lysis. Cyanobacterial lawns showed no plaques. Thin sections of two amoeba showed food vacuoles containing what appeared to be virus particles of a type seen in certain prokaryotic and eukaryotic cells in the biomass. [TOP OF PAGE]
[Phagolysates of cyanobacteria: their biocidal properties and use]. Gol'din,E.B., Mendzhul,M.I. (1996). Mikrobiol. Zh. 58:51-58. Data on the biological activity of cyanobacterial phagolysates were obtained in experiments. They concern the organisms of different evolutional level, such as some conventional pathogenic bacteria, plant and root parasitic nematodes and phytophagous insects. The authors suppose the specific mechanism of biocidal and inhibitory action of cyanobacteria and their phagolysates in respect to different living systems. These facts are very important for the elaboration of practical aspects of algal metabolites employment in agriculture and medicine. [TOP OF PAGE]
Evidence that the hanA gene coding for HU protein is essential for heterocyst differentiation in, and cyanophage A-4(L) sensitivity of, Anabaena sp. strain PCC 7120. Khudyakov,I., Wolk,C.P. (1996). Journal of Bacteriology [J. BACTERIOL. ] 178:3572-3577. The highly pleiotropic, transposon-generated mutant Anabaena sp. strain PCC7120 exhibits slow growth, altered pigmentation, cellular fragility, resistance to phage A-4(L), and the inability to differentiate heterocysts. Reconstruction of the transposon mutation in the wild-type strain reproduced the phenotype of the original mutant. Sequencing of the flanking DNA showed that the transposon had inserted at the beginning of a gene, which we call hanA, that encodes Anabaena HU protein. Mapping of the transposon insertion by pulsed-field gel electrophoresis showed that hanA is located at ca. 4.76 Mb on the physical map of the chromosome and is transcribed clockwise. Repeated subculturing of of filament fragmentation, presumably because of one or more compensatory mutations; however, the mutant retained its A-4(L) super(r) Het super(-) phenotype. The mutation in strain be complemented by a fragment of wild-type DNA bearing hanA as its only open reading frame. [TOP OF PAGE]
Wastewater treatment and elimination of pathogens: new prospects for an old problem. Lopez-Pila,J.M., Dizer,H., Dorau,W. (1996). Microbiologia 12:525-536. Although the development of wastewater treatment technology is more than one hundred years old, most wastewater treatment plants existing today do not eliminate pathogens satisfactorily. Even in highly developed nations, receiving waters, serving in many cases as drinking water resources, are contaminated with pathogens. Surface waters also contain large concentration of phosphate due to long lasting wastewater discharges. Cyanobacteria and algal overgrowth is the consequence. Present drinking water technology only partially overcomes the pollution; it can not be ruled out that drinking water originating from polluted resources contains pathogens. This situation frequently goes on unnoticed because current indicator organisms are not representative for all pathogens. As studies have shown that small concentrations of pathogens also pose a risk for the consumer health, this state of affairs is a matter of concern. Microfiltration technology is able to significantly eliminate bacteria and protists from wastewater. Viruses, although smaller than the pore size of the filters, are reduced too because, in wastewater, they are frequently bound to larger particles. If the microfiltration of wastewater is preceded by the addition of coagulants for the precipitation of phosphate, the precipitate will be retained by the filter. The effluent obtained contains very low concentrations of phosphate. As viruses also adsorb to the precipitate, the amount of viruses eliminated increases and with increasing amounts of coagulant they become undetectable. [TOP OF PAGE]
Occurrence of a temperate cyanophage lysogenizing the marine cyanophyte Phormidium persicinum. Ohki,K., Fujita,Y. (1996). J. Phycol. 32:365-370. A temperate cyanophage was found to lysogenize the marine cyanophyte Phormidium persicinum (Reinke) Gom. (Provasoli strain). The lytic cycle was induced by the addition of mitomycin C or by brief illumination with ultraviolet light. The lytic process observed under the electron microscope showed that phage particles appeared in a nucleoplasm region 15 to 24 h after the addition of mitomycin C. The induction of the lytic process occurred simultaneously in almost all cells of every trichome. Matured phage particles were released to the medium 30 to 50 h after the addition of mitomycin C Phage particles isolated from algal lysates had a polyhedral head (about 40 nm in diameter) with a long (about 300 nm) and noncontractile tail. The most abundant protein, presumably a structural protein, had an apparent molecular mass of about 38 kDa. The genome size estimated from restriction analysis was about 50 kbp. Phage DNA was digested with several restriction endonucleases including Sau3AI and DpnI. However, MboI failed to digest the pha DVA, suggesting that the phage DNA is highly methylated. Southern blot analysis suggested that some part of the phage was in the lytic cycle in algal cells growing under normal conditions. A possible role of temperate cyanophages in the regulation of cyanophyte populations in the marine environment is discussed. [TOP OF PAGE]
Temporal and spatial dynamics of Synechococcus spp. and Micromonas pusilla host-viral systems. Rodda,K.M. (1996). University of Texa at Austin. [TOP OF PAGE]
Unusual contribution of 2-aminoadenine to the thermostability of DNA. Sagi,J., Szakonyi,E., Vorlickova,M., Kypr,J. (1996). J Biomol Struct Dyn 13:1035-1041. The poly(dA-dU) and poly(dI-dC) duplexes have very similar thermostabilities (Tm). This similarity extends also to the pyrimidine 5-methyl group-containing poly(dA-dT) and poly(dI-m5dC). The differences between chemical structures of the A:U and I:C or the A:T and I:m5C base-pairs seem to be unimportant for the thermostability of the DNA. However, on the insertion of an amino group into position 2 of the purines the similarities disappear. Thermostabilities of poly(n2dA-dU) and poly(dG-dC) as well as the poly(n2dA-dT) and poly(dG-m5dC) are radically different. This is also the case with their other 5-substituted pyrimidine-containing derivatives, the 5-ethyl, 5-n-butyl and 5-bromo analogues. The G:C-based polynucleotides are more stable by an average of 40 degrees C than the n2A.U-based ones. Poly(dA,n2dA-dT)-s containing various proportions of A and n2A as well as the natural DNA of S-2L cyanophage that contains n2A bases instead of A were also studied. It was found that dependence of Tm on the n2A-content was non-linear and that the lower Tm is not the consequence of a particular nucleotide sequence. The possible structural reasons for the lower thermostabilization of these B-DNAs by the n2A:T base-pair as compared to the G:C are discussed. [TOP OF PAGE]
The effect of cyanophages on Synechococcus spp. during a bloom in the western Gulf of Mexico. Suttle,C.A., Chan,A.M., Rodda,K.M., Short,S.M., Weinbauer,M.G., Garza,D.R., Wilhelm,S.W. (1996). EOS 76 (suppl.):OS207-OS208 [TOP OF PAGE]
The effects of nutrient limitation on the kinetics of cyanophage infection of the oceanic picoplankter Synechococcus sp. WH7803. Wilson,S.H., Carr,N.G., Mann,N.H. (1996). J. Phycol. 32:506-516. Phycoerythin-containing Synechococcus species are considered to be major primary producers in nutrient-limited gyres of subtropical and tropical oceanic provinces, and the cianophages that infect them are thought to influence marine biogeochemical cycles. This study begins an examination of the effects of nutrient limitation on the dynamics of cjanophage/Synechococcus interactions in oligotrophic environments by analyzing the infection kinetics of cyanophage strain S-P1kf2 (Cyanomyoviridae isolated from coastal water off Plymouth, UK) propagated on Synechococcus sp. WH7803 grown in either phosphate-deplete or phosphate-replete conditions. When the growth of Synechococcus sp. WH7803 in phosphate deplete medium was followed after injection with cyanophage, an 18-h[???} delay in cell Iysis was observed when compared to a phosphate-replete control. Synechococcus sp. WH7803 cultures grown at tu10 different rates (in the same nutritional conditions) both lysed 24 h postinfection, ruling out growth rate itself as a factor in the delay of cell lysis. One-step growth kinetics of S-PA\/12 propagated on host Synechococcus sp. W'H7803, grow in phosphate deplete and-replete media, revealed an apparent 80% decrease in burst size in phosphate-deplete growth conditions, but phage adsorption kinetics of S-PM2 under these conditions showed no differences. These results suggested that the cyanophages established lysogeny in response to phosphate-deplete growth of host cells. This suggestion was supported by comparison of the proportion of infected cells that lysed under phosphate-replete and-deplete conditions, which revealed that only 9.3% of phosphate-deplete infected cells lysed in contrast to 100% of infected phosphate-replete cells. Further studies with two independent cyanophage strains also revealed that only approximately 10% of infected phosphate-deplete host cells released progeny cyanophages. These data strongly support the concept that the phosphate status of the Synechococcus cell will have a profound effect on the eventual outcome of phage-host interactions and will therefore exert a similarly extensive effect on the dynamics of carbon flow in the marine environment. [TOP OF PAGE]
The effect of phosphate status on the kinetics of cyanophage infection in the oceanic cyanobacterium Synechococcus sp. WH7803. Wilson,W.H., Carr,N.G., Mann,N.H. (1996). J. Phycol. 32:506-516. Phycoerythrin-containing Synechococcus species are considered to be major primary producers in nutrient-limited gyres of subtropical and tropical oceanic provinces, and the cyanophages that infect them are thought to influence marine biogeochemical cycles. This study begins an examination of the effects of nutrient limitation on the dynamics of cyanophage/Synechococcus interactions in oligotrophic environments by analyzing the infection kinetics of cyanophage strain S-PM2 (Cyanomyoviridae isolated from coastal water off Plymouth, UK) propagated on Synechococcus sp. WH7803 grown in either phosphate-deplete or phosphate-replete conditions. When the growth of Synechococcus sp. WH7803 in phosphate-deplete medium was followed after infection with cyanophage, an 18-h delay in cell lysis was observed when compared to a phosphate-replete control. Synechococcus sp. WH7803 cultures grown at two different rates (in the same nutritional conditions) both lysed 24 h postinfection, ruling out growth rate itself as a factor in the delay of cell lysis. One- step growth kinetics of S-PM2 propagated on host Synechococcus sp. WH7803, grown in phosphate-deplete and- replete media, revealed an apparent 80% decrease in burst size in phosphate-deplete growth conditions, but phage adsorption kinetics of S-PM2 under these conditions showed no differences. These results suggested that the cyanophages established lysogeny in response to phosphate-deplete growth of host cells. This suggestion was supported by comparison of the proportion of infected cells that lysed under phosphate-replete and-deplete conditions, which revealed that only 9.3% of phosphate-deplete infected cells lysed in contrast to 100% of infected phosphate replete cells. Further studies with two independent cyanophage strains also revealed that only approximately 10% of infected phosphate-deplete host cells released progeny cyanophages. These data strongly support the concept that the phosphate status of the Synechococcus cell will have a profound effect on the eventual outcome of phage-host interactions and will therefore exert a similarly extensive effect on the dynamics of carbon flow in the marine environment. [TOP OF PAGE]
A study on cyanophages inhibiting the growth of algae producing musty odor. Goto,Y., Kitayama,M. (1995). Water Supply 13:263-266. Recently blue-green algae have grown in large amount in the Lake Biwa. Authors have carried out a study on the cyanophages, which use Phormidium tenue (P. tenue), blue-green alga that produce musty odor in the Lake Biwa, as host and inhibit their growth. The samples used consisted of the surface-layer water in the Lake or the surface running water in Kizu River and Katsura River. A plate culture test by using the double-layered agar method was used in order to detect cyanophages, and the generation of plaque was observed. And, in order to confirm that the cyanophages inhibit the growth of P. tenue, authors also realized a liquid culture test, and observed the growth characteristics of the host. For the plate culture test, three samples presented the formation of plaque. In the liquid culture test, the growth of P. tenue was found to have been inhibited in the three samples. But for all these three samples, P. tenue was not completely killed; therefore, these cyanophages were believed to be temperate phages. By using these cyanophages is expected to be able to inhibit the growth of P. tenue alone without inhibiting the growth of other algae. [TOP OF PAGE]
Fluorescently labeled virus probes show that natural virus populations can control the structure of marine microbial communities. Hennes,K.P., Suttle,C.A., Chan,A.M. (1995). Appl. Environ. Microbiol. 61:3623-3627. Fluorescently stained viruses were used as probes to label, identify and enumerate specific strains of bacteria and cyanobacteria in mixed microbial assemblages. Several marine virus isolates were fluorescently stained with YOYO-1 or POPO-1 (Molecular Probes, Inc.) and added to seawater samples that contained natural microbial communities. Cells to which the stained viruses adsorbed were easily distinguished from non-host cells; typically, there was undetectable binding of stained viruses to natural microbial assemblages containing >10⁶ bacteria ml^-1, but to which host cells were not added. Host cells that were added to natural seawater were quantified with 99 ± 2 % efficiency using fluorescently labeled virus probes (FLVPs). A marine bacterial isolate (strain PWH3a) was introduced into natural microbial communities that were either supplemented with nutrients or untreated, and changes in the abundance of the isolate were followed using FLVPs. Simultaneously, the concentration of viruses that infected strain PWH3a was monitored by plaque assay. Following the addition of PWH3a, viruses infecting this strain increased from undetectable levels (<1 ml^-1 to 2.9 x 10⁷ ml^-1 and 8.3 x 10⁸ ml^-1 for the untreated and nutrient-enriched samples, respectively. The increase in viruses was associated with a collapse in populations of strain PWH3a from ca. 30% to 2% and 43% to 0.01% of the microbial communities in untreated and nutrient-enriched samples, respectively. These results clearly demonstrate that FLVPs can be used to identify and quantify specific groups of bacteria in mixed microbial communities. As well, the data show that viruses which are present at low abundances in natural aquatic viral communities can control microbial community structure. [TOP OF PAGE]
Direct counts of viruses in natural waters and laboratory cultures by epifluorescence microscopy. Hennes,K.P., Suttle,C.A. (1995). Limnol. Oceanogr. 40:1050-1055. Epifluorescent microscopy was used to determine the abundance of viruses in samples from marine and freshwater environments and in laboratory cultures that were filtered onto 0.02-µm pore-size filters and stained with a cyanine-based dye (Yo-Pro-1). Estimates of viral abundance based on Yo-Pro stained samples were 1.2 to 7.1 times greater than estimates obtained using transmission electron microscopy (TEM). Moreover, the precision of the Yo-Pro based method was much greater than that for TEM (coefficient of variation 7 % versus 20 %, respectively). DNase treatment of samples did not result in lower numbers of particles that could be stained by Yo-Pro, suggesting that the fluorescence was not the result of nucleic acids associated with the surface of particles. These results indicate that the concentration of viruses in natural waters may be higher than previously recognized and imply that the TEM-based method significantly underestimates virus abundance. Virus abundances ranged from 10⁷ to > 10⁸ ml^-1 in surface waters along a transect in the western Gulf of Mexico to 10⁹ ml^-1 in water overlying a submerged cyanobacterial mat. High counting efficiency, ease of preparation, modest equipment requirements and the possibility of preparing specimens for long-term storage, make the Yo-Pro based method ideal for routine environmental analysis. [TOP OF PAGE]
Complete nucleotide sequence of the gene encoding bacteriophage E endosialidase: implications for K1E endosialidase structure and function. Long,G.S., Bryant,J.M., Taylor,P.W., Luzio,J.P. (1995). Biochem. J. 309 ( Pt 2):543-550. Bacteriophage E specifically recognizes and infects strains of Escherichia coli which display the alpha-2,8-linked polysialic acid K1 capsule. Bacteriophage E endosialidase, which is thought to be responsible for initial absorption of the phage to the host bacterium, was purified, and the N-terminal amino acid sequences of the polypeptide monomer and cyanogen bromide fragments were determined. Synthetic oligonucleotide probes were designed from the N-terminal amino acid sequences and used to identify restriction fragments of bacteriophage E DNA encoding the endosialidase. The primary nucleotide sequence of the bacteriophage E endosialidase gene contains an open reading frame encoding a 90 kDa polypeptide which is processed to give a mature 74 kDa protein. The native enzyme is probably a trimer of identical 74 kDa subunits. In the bacteriophage E genome the K1E endosialidase open reading frame is preceded by a putative upstream promoter region with homology to a bacteriophage SP6 promoter. A central region of 500 amino acids of the deduced protein sequence of the K1E endosialidase was found to have 84% identity to K1F endosialidase. Both endosialidases contain two copies of a sialidase sequence motif common to many bacterial and viral sialidases. These sequences flank the region of greatest identity between the two endosialidase forms, which suggests that this central domain is involved in binding and hydrolysis of the polysialic acid substrate. [TOP OF PAGE]
Viral abundance in aquatic systems: a comparison between marine and fresh waters. Maranger,R., Bird,D.F. (1995). Mar. Ecol. Prog. Ser. 121:1-3. In order to investigate the factors controlling viral abundance, 22 lakes in Quebec were surveyed. We measured viral and bacterial abundance, bacterial production, chlorophyll a, total phosphorus and DOC (dissolved organic carbon) concentrations. Regression models built with these data were compared to models based on literature data, which to date have been collected largely from marine sites. Positive empirical relationships were found between viral abundance and (1) chlorophyll a concentrations, (2) bacterial abundances, (3) bacterial production, and (4) total phosphorus concentration. There was little to no trend in the virus-to-bacteria ratio with increasing trophy. Analysis of covariance revealed significant differences between relations in marine and freshwater systems. The virus-to-bacteria ratio was significantly higher in freshwater (mode = 22.5) than marine environments (mode = 2.5), and there were significantly more bacteria per unit chlorophyll in our freshwater samples. We suggest that this difference is related to the increased dependence of freshwater bacteria on allochthonous material relative to marine systems, as well as the increased relative importance of photosynthetic cyanobacteria in lakes. [TOP OF PAGE]
[Effect of reproduction of the LPP-3 cyanophage on glutamate dehydrogenase and glutamine synthetase activity in the cyanobacterium Plectonema boryanum]. Mendzhul,M.I., Koltukova,N.V., Lysenko,T.G., Shainskaia,O.A., Perepelitsa,S.I. (1995). Ukr Biokhim Zh 67:33-37. The effect of cyanophage LPP-3 reproduction on glutamate dehydrogenase and glutamine synthetase (GS) in P boryanum cells have been studied. It was determined that the both reactions are intensified by 135% and 220%, accordingly. Isoenzymes of GS were purified from native and infected cell of cyanobacteria. Their physical-and-chemical properties are different. The cyanophage development probably causes specific modification of the cell enzymes. [TOP OF PAGE]
[Alanine dehydrogenase of the cyanobacterium Plectonema boryanum in the early period of cyanophage LPP-3 development]. Perepelitsa,S.I., Koltukova,N.V., Mendzhul,M.I. (1995). Ukr Biokhim Zh 67:47-52. It has been studied how reproduction of LPP-3 in Plectonema boryanum cells influences the alanine dehydrogenase activity. It has been found that immediately after the virus adsorption the enzyme activity falls by 50% and the anabolic reaction is blocked. Physicochemical properties of the enzyme vary as well. An infected cell has one isoenzyme-octamer with pl 9.1-9.2, pH-optimum by action 9-10, molecular weight about 27 kDa. [TOP OF PAGE]
Characterization of TS-mutants of cyanophage N-1 by their inactivation by physical and chemical agents. Sarma,T.A., Singh,R. (1995). Acta Virol. 39:65-68. The effect of temperature, ultraviolet (UV) light and ethylenediaminetetraacetic acid (EDTA) on the stability of cyanophage N-1, infecting the cyanobacterium Nostoc muscorum was studied. Complete inactivation of the phage occurred at 60 degrees C in 6 mins. All the temperature-sensitive (ts) mutants exhibited faster inactivation at 50 degrees C than the wild type. UV light readily inactivated the particles of the wild giving a survival of 3.44% at a dose of 60 secs. All the ts-mutants were found to be more sensitive to UV light than the wild type. 10(-4) mol/l EDTA inactivated 40% of the wild type in 60 mins. 5 x 10(-4) mol/l EDTA inactivated the wild type nearly completely within 2 mins, while a similar inactivation of ts-mutants required only 90 secs. [TOP OF PAGE]
A New Synechococcus Cyanophage from a Reservoir in Korea. Kim,M., Choi,Y.-K. (1994). Virology 204:338-342. A unicellular cyanobacterium (Synechococcus) and its cyanophage were both isolated from a reservoir in Korea. Although morphologically similar to AS-1, the cyanophage differs from cyanophage AS-1 in some respects. The burst size in the light is approximately 100 plaque-forming units (PFU)/cell. Replication of the virus also occurs in the dark, releasing about 10% of the virus particles observed in the light. Na+ is not necessary for adsorption. [TOP OF PAGE]
[Aspartate kinase complex of Anabaena variabilis during the early period of development of cyanophage A-1]. Koltukova,N.V., Kadyrova,G.K., Lysenko,T.G., Mendzhul,M.I. (1994). Ukr Biokhim Zh 66:41-48. Aspartate kinase activity in cells of A. variabilis has been studied in the dynamics of development of virus infection. An early period of reproduction of cyanophage A-1 has been determined to be conjugated with the increase of biosynthesis of amino acids from aspartate family. Five isoenzymes of aspartate kinase were isolated and purified from A. variabilis cells during early development period of cyanophage A-1. Physicochemical properties and influence of amino acids of aspartate family on the activity of homogeneous isoenzymes have been studied. Retroinhibition effect was not observed in infected cyanobacteria cells, which probably enables one to increase 2-7 times the concentration of amino acids in a cell. Such an increase of the amino acids pool is apparently necessary for realization of viral genome strategy. [TOP OF PAGE]
Isolation and characterization of temperature-sensitive mutants of cyanophage N-1. Sarma,T.A., Singh,R. (1994). Acta Virol 38:11-16. Optimal conditions for the induction of temperature-sensitive (ts) mutants of cyanophage N-1 were established after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). A treatment with MNNG (400 micrograms/ml) for 2 hrs at pH 8.0 induced ts-mutants at a maximum frequency of 1.46 x 10(-3). A characterization of 10 such ts-mutants with regard to adsorption, one-step growth and temperature-shift experiments with Nostoc muscorum as host bacterium led to the identification of temperature-sensitive steps in the phage multiplication at the restrictive temperature (37 degrees C). All the mutants were found to be conditionally lethal at 37 degrees C since they resumed growth upon shifting to 28 degrees C. [TOP OF PAGE]
Energetics of cyanophage N-1 multiplication in the diazotrophic cyanobacterium Nostoc muscorum. Singh,S., Bhatnagar,A., Kashyap,A.K. (1994). Microbios 78:259-265. Cyanophage N-1 multiplication was investigated during the latent period of the virus, when super(14)CO sub(2) fixation was inhibited whereas respiratory O sub(2) uptake increased similar to 67% at 4 h after infection. A simultaneous decrease (70%) in the glycogen content of infected cells indicated its catabolic involvement. A chloramphenicol-sensitive rise in glucose-6-phosphate dehydrogenase activity as a result of N-1 infection partly explained the increase in aerobic respiration. The total ATP pool declined to 53% of the control while Ca super(2+)-dependent ATPase activity also declined (25%). In contrast, Mg super(2+)-dependent ATPase activity increased (80%) in comparison with uninfected cells. Results suggest that oxidative phosphorylation was more crucial in the control of cyanophage N-1 development than photophosphorylation under photoautotrophic growth conditions. [TOP OF PAGE]
Isolation of a marine cyanophage infecting the marine unicellular cyanobacterium, Synechococcus sp. NKBG 042902. Sode,K., Oozeki,M., Asakawa,K., Burgess,J.G., Matsunaga,T. (1994). J. Mar. Biotechnol. 1:189-192. A marine cyanophage that infects the marine unicellular cyanobacterium, Synechococcus sp. NKBG 042902, was isolated from seawater. This marine cyanophage possesses a tail with a contractile sheath, which shows two distinct shapes, and is a temperate narrow host range phage that can be induced by mitomycin C. It is distinct from the cyanophage AS-1, which infects the freshwater strain Anacystis nidulans R2, with regard to host range and restriction enzyme pattern, and is designated as mS-1 (marine Synechococcus infecting). [TOP OF PAGE]
Dynamics and distribution of cyanophages and their effect on marine Synechococcus spp. Suttle,C.A., Chan,A.M. (1994). Appl. Environ. Microbiol. 60:3167-3174. Cyanophages infecting marine Synechococcus were frequently very abundant and were found in every seawater sample along a transect in the western Gulf of Mexico, and during a 28 month period in Aransas Pass, Texas. In Aransas Pass their abundance varied seasonally with the lowest concentrations coincident with cooler water and lower salinity. Along the transect, viruses infecting Synechococcus strains DC2 and SYN48 ranged in concentration from a few hundred ml^-1 at 97 m depth and 83 km offshore, to ca. 4 x 10⁵ ml^-1 near the surface at stations within 18 km of the coast. The highest concentrations occurred at the surface where salinity decreased from ca. 35.5 to 34 ppt and concentrations of Synechococcus were greatest. Viruses infecting strains SNC1, SNC2 and 838BG were distributed in a similar manner, but were much less abundant (< 10 to > 5 x 10³ ml^-1). When Synechococcus exceeded ca. 10³ ml^-1, cyanophage concentrations increased markedly (ca. 10² to > 10⁵ ml^-1), suggesting that there was a minimum host density required for efficient viral propagation. Data on the decay rate of viral infectivity (d; d-1) as a function of solar radiation (I; mmol quanta m^-2 s^-1) was used to develop a relationship (d = 0.2610 I - 0.00718; r² = 0.69) for conservatively estimating the destruction of infectious viruses in the mixed layer of two offshore stations. Assuming that virus production balances losses, and burst size is 250, ca. 5-7 % of Synechococcus would be infected daily by viruses. Calculations based on contact rates between Synechococcus and infectious viruses produce similar results (5-14 %). Moreover, balancing estimates of viral production with contact rates for the most offshore station required that most Synechococcus be susceptible to infection, that most contacts result in infection and that the burst size be about 324 viruses per lytic event. In contrast, in nearshore waters where ca. 80 % of Synechococcus would be contacted daily by infectious cyanophages, only ca. 1 % of the contacts would have to result in infection, in order to balance the estimated virus removal rates. These results indicate that cyanophages are an abundant and dynamic component of marine planktonic communities and are likely responsible for lysing a small but significant portion of the Synechococcus population on a daily basis. [TOP OF PAGE]
[The resistance of the DNA of cyanophage LPP-3 to the action of different restriction endonucleases]. Mendzhul,M.I., Syrchin,S.A., Rebentish,B.A., Averkiev,A.A., Busakhina,I.V. (1993). Mikrobiol. Zh. 55:47-53. Data on the study of structure peculiarities of cyanophage LPP-3 DNA are presented in the work. The length of cyanophage DNA calculated by means of the enzymatic hydrolysis by restrictases is 40 +/- 3.5 thou. pairs of bases. Cyanophage LPP-3 DNA was hydrolysed by more than 50 different restrictases. As a result of screening it was found out that the great number of restrictases, which recognized hexanucleotide sequences did not hydrolyze DNA of cyanophage LPP-3. A considerable deviation of the number of the observed sites of restriction from their theoretically expected number for restrictases Hae III and Cfr 131 was established. Restrictases-isoschisomeres with different sensitivity to the methylation of the recognition sites--Msp I, Hpa II and Sau 3A, MboI and DpnI were used to check the availability of methylated bases in LPP-3 DNA. Absence of methylated adenine in the site GATC and methylated cytosine in the second position of the site CCGG were established. The results obtained permit supposing that the expressed counterselection by the sites of recognition of many restriction endonucleases takes place in cyanophage LPP-3 DNA. It is supposed that apparently, this method of protection of its genome in LPP-3 is one of most important but the inconsiderable percentage of site-specific methylation of the virus DNA cannot be completely excluded. [TOP OF PAGE]
Spontaneous and induced host range mutants of cyanophage N-1. Sarma,T.A., Kaur,B. (1993). Arch Virol 130:195-200. Optimal conditions for the induction of host-range mutants of cyanophage N-1 by acridine orange were established. Induced host-range mutants were isolated with a frequency of 0.1 to 4.0 x 10(-5) over a spontaneous mutation frequency of 0.2-3.6 x 10(-11). [TOP OF PAGE]
Cyanophages and sunlight: A paradox. Suttle,C.A., Chan,A.M., Chen,F., Garza,D.R. (1993). pp. 303-307. In In Guerrero,R. and Pedros-Alio,C. (eds.), Trends in Microbial Ecology. Spanish Society Microbiology, Barcelona. [TOP OF PAGE]
Marine cyanophages infecting oceanic and coastal strains of Synechococcus: Abundance, morphology, cross-infectivity and growth characteristics. Suttle,C.A., Chan,A.M. (1993). Mar. Ecol. Prog. Ser. 92:99-109. Eight different phycoerythrin- and phycocyanin-containing strains of Synechococcus and one strain of Anacystis were screened against 29 natural virus communities taken from 3 locations in south Texas coastal waters, at different times of the year. In addition, one sample was screened from Peconic Bay, New York. Cyanophages were detected in all samples, but the frequency with which they were detected and their abundance depended upon the strain of Synechococcus that was screened. Viruses that infected red Synechococcus strains were particularly common. In some instances, concentrations infecting a single Synechococcus strain were in excess of 10⁵ ml^-1. The abundances of cyanophages were weakly correlated with temperature (r² = 0.53 to 0.70), although they occurred at all of the temperatures (12-30.4^oC) and salinities (18-70 ppt) that were screened. The seven cyanophages that were cloned belonged to the same three families of viruses that have been observed to infect freshwater cyanobacteria, namely the Siphoviridae (formerly Styloviridae), Myoviridae and Podoviridae. The cyanophage clones varied in host-specificity. For example, one clone infected a single Synechococcus strain of 12 that were tested, whereas, another infected 4 of 9 strains tested. Growth characteristics of one of the virus clones was determined for a single host. Photosynthesis in Synechococcus was not affected until near the onset of cell lysis and the virus burst cycle was complete about 17 h post-infection. The burst size was approximately 250 infective particles. The high abundance of cyanophages in the natural environment provides further evidence that viruses are probably important regulators of phytoplankton dynamics in marine systems. [TOP OF PAGE]
Resistance to co-occurring phages enables marine Synechococcus communities to coexist with cyanophages abundant in seawater. Waterbury,J.B., Valois,F.W. (1993). Appl. Environ. Microbiol. 59:3393-3399. Recent reports documenting very high viral abundances in seawater have led to increased interest in the role of viruses in aquatic environments and a resurgence of the hypothesis that viruses are significant agents of bacterial mortality. Synechococcus spp., small unicellular cyanobacteria that are important primary producers at the base of the marine food web, were used to assess this hypothesis. We isolated a diverse group of Synechococcus phages that at times reach titers of between 10 super(3) and 10 super(4) cyanophages per ml in both inshore and offshore waters. However, despite their diversity and abundance, we present evidence in support of the hypothesis that lytic phages have a negligible effect in regulating the densities of marine Synechococcus populations. Our results indicate that these bacterial communities are dominated by cells resistant to their co-occurring phages and that these viruses are maintained by scavenging on the relatively rare sensitive cells in these communities. [TOP OF PAGE]
Isolation and molecular characterization of five marine cyanophages propagated on Synechococcus sp. strain WH7803. Wilson,W.H., Joint,I.R., Carr,N.G., Mann,N.H. (1993). Appl. Environ. Microbiol. 59:3736-3743. Five marine cyanophages propagated on Synechococcus sp. strain WH7803 were isolated from three different oceanographic provinces during the months of August and September 1992: coastal water from the Sargasso Sea, Bermuda; Woods Hole harbor, Woods Hole, Mass.; and coastal water from the English Channel, off Plymouth Sound, United Kingdom. The five cyanophage isolates were found to belong to two families, Myoviridae and Styloviridae, on the basis of their morphology observed in the transmission electron microscope. DNA purified from each of the cyanophage isolates was restricted with a selection of restriction endonucleases, and three distinguishably different patterns were observed. DNA isolated from Myoviridae isolates from Bermuda and the English Channel had highly related restriction patterns, as did DNA isolated from Styloviridae isolates from Bermuda and the English Channel. DNA isolated from the Myoviridae isolate from Woods Hole had a unique restriction pattern. The genome size for each of the Myoviridae isolates was ca. 80 to 85 kb, and it was ca. 90 to 100 kb for each of the Styloviridae isolates. Southern blotting analysis revealed that there was a limited degree of homology among all cyanophage DNAs probed, but clear differences were observed between cyanophage DNA from the Myoviridae and that from the Styloviridae isolates. Polypeptide analysis revealed a clear difference between Myoviridae and Styloviridae polypeptide profiles, although the major, presumably structural, protein in each case was ca. 53 to 54 kDa. [TOP OF PAGE]
The inhibitory effects of the extracts of Zingiber plants on the adsorption, growth, and replication of phage LPP-1 in cyanobacterium. Jido,E.P. (1992). Loyola University of Chicago. [TOP OF PAGE]
Effect of reproduction of cyanophages A-1, S-8K and LPP-3 on proteolysis processes in the cells of cyanobacteria. Mendzhul,M.I., Koltukova,N.V., Lysenko,T.G., Shainskaya,O.A. (1992). Mikrobiol. Zh. 54:90-95. The dynamics of proteolytic activity and formation of protein metabolism products (free aminoacids and peptides) in three virus-cell systems (Anabaena variabilis - A-1, Synechococcus cedrorum-S-8K, Plectonema boryanum - LPP-3) have been studied as affected by cyanophage infection. Proteolytic activity of the cell-free extracts of cyanobacteria is established to considerably change during the cyanophage development. Preparations isolated from the cells 1h after infection are the most active ones. Proteolytic activity of the cells 3h after the infection (period of intensive morphogenesis of virions) is almost commensurable with that of the noninfected cells. The level of proteolytic activity and the content of free aminoacids and peptides well correlate only in the system LPP-3-P. boryanum. Such an agreement was not revealed in two other-virus-cellular systems and this is, probably, connected with different specificity of proteinases, which perform degradation of cell proteins, and with the differences in the processes of the de novo synthesis of amino acids and proteins. Various ways and mechanisms, including proteolysis-performed by virus-induced proteinases, may be involved in formation of a pool of free aminoacids in different virus-cellular systems. [TOP OF PAGE]
The effect of cyanophages on the growth and survival of Lyugbya wollei, Anabaenaflos- aquae, and Anabaena circinalis. Monegue,R.L., Phlips,E.J. (1991). J. Aquat. Plant. Manage. 29:88-93. Not sure if following constitutes abstract: Three newly isolated cyanobacteria viruses tested on hHe organisms in laboratory culture experiments. “Cyanophage LW 1 significantly reduced the growth and survival of L. toollei....” Inhibition of growth occurred within 7 days and chlorophyll a concentrations were reduced 95% (relative to controls) within 14 days of inoculahon. (quoted from http://nosferatu.cas.usf.edu/chemistry/info_research_resources/ies/LYNGBYA.html). [TOP OF PAGE]
Roles of viral infection in organic particle flux. Proctor,L.M., Fuhrman,J.A. (1991). Mar. Ecol. Prog. Ser. 69:133-142. Lack of information on the fate of particulate-associated microorganisms prompted this investigation of viruses (including bacteriophage or phage) and phage-infected cells in sinking particles from sediment traps. Sediment trap material from 30 to 400 m collected from the north Pacific Ocean during the 'VERTEX' cruises in 1980 to 1982 was examined by transmission electron microscopy. Viruses were present in all of the sinking particles examined except for those from one sample, of highly degraded algal cells or small fecal pellets, from 400 m. Viruses in the sinking particles often appeared aggregated. From 0.7 to 3.7% of the bacteria in sinking particles contained mature phage; from these data and limited information from pure cultures, we estimate that 2 to 37% of the particulate-associated bacteria may be killed by viral lysis. Many eukaryotic cells were also apparently infected with viruses, but none (.ltoreq. 50 cells observed) of the cyanobacteria or 'Chlorella-like' cells appeared infected. Viral lysis of bacteria associated with sinking particles and free-living bacteria may be causally linked and may play a role in dissolved organic carbon production and the dynamics of sinking particles. Viral lysis may have major implications for understanding cycling of material and energy in the ocean. [TOP OF PAGE]
Analysis of marine picoplankton community by 16S ribosomal-RNA gene cloning and sequencing. Schmidt,T.M., Delonge,E.F., Pace,N.R. (1991). J. Bacteriol. 173:4371-4378. The phylogenetic diversity of an oligotrophic marine picoplankton community was examined by analyzing the sequences of cloned ribosomal genes. This strategy does not rely on cultivation of the resident microorganisms. Bulk genomic DNA was isolated from picoplankton collected in the north central Pacific Ocean by tangential flow filtration. The mixed-population DNA was fragmented, size fractionated, and cloned into bacteriophage lambda. Thirty-eight clones containing 16S rRNA genes were identified in a screen of 3.2 x 10(4) recombinant phage, and portions of the rRNA gene were amplified by polymerase chain reaction and sequenced. The resulting sequences were used to establish the identities of the picoplankton by comparison with an established data base of rRNA sequences. Fifteen unique eubacterial sequences were obtained, including four from cyanobacteria and eleven from proteobacteria. A single eucaryote related to dinoflagellates was identified; no archaebacterial sequences were detected. The cyanobacterial sequences are all closely related to sequences from cultivated marine Synechococcus strains and with cyanobacterial sequences obtained from the Atlantic Ocean (Sargasso Sea). Several sequences were related to common marine isolates of the gamma-subdivision of proteobacteria. In addition to sequences closely related to those of described bacteria, sequences were obtained from two phylogenetic groups of organisms that are not closely related to any known rRNA sequences from cultivated organisms. Both of these novel phylogenetic clusters are proteobacteria, one group within the alpha-subdivision and the other distinct from known proteobacterial subdivisions. The rRNA sequences of the alpha-related group are nearly identical to those of some Sargasso Sea picoplankton, suggesting a global distribution of these organisms. [TOP OF PAGE]
Promoter recognition by the RNA polymerase from vegetative cells of the cyanobacterium Anabaena 7120. Schneider,G.J., Lang,J.D., Haselkorn,R. (1991). Gene 105:51-60. The transcription start points (tsp) of seven genes of Anabaena 7120 were previously identified by S1 nuclease protection and primer extension experiments using RNA extracted from cells. In the present work, these tsp were confirmed, with one exception, by in vitro transcription using purified RNA polymerases of Anabaena 7120 and Escherichia coli, and crude extracts of Anabaena 7120 active in transcription. In all cases, the template for transcription consisted of closed circular plasmid DNA in which the putative promoter-containing fragment was cloned in front of a strong terminator, which resulted in defined 'pseudo-runoff' transcripts whose sizes correspond (with one exception) to those expected on the basis of the tsp determined for in vivo RNA. These results, together with others obtained with templates containing bacteriophage T4 or cyanophage N1 promoters, led to the conclusion that the principal Anabaena 7120 RNA polymerase prefers promoters whose sequence and spacing approximate that of the E. coli consensus promoter, and that the Anabaena 7120 genes expressed in vegetative cells, characterized to date, have relatively weak promoters. [TOP OF PAGE]
Use of ultrafiltration to isolate viruses from seawater which are pathogens to marine phytoplankton. Suttle,C.A., Chan,A.M., Cottrell,M.T. (1991). Appl. Environ. Microbiol. 57:721-726. Viruses may be major structuring elements of phytoplankton communities, and hence important regulators of nutrient and energy flux in aquatic environments. In order to ascertain if viruses are potentially important in dictating phytoplankton community structure, it is essential to determine the extent to which representative phytoplankton taxa are susceptible to viral infection. We used a spiral ultrafiltration cartridge (30,000 MW cutoff) to concentrate viruses from seawater at efficiencies approaching 100 %. Natural virus communities were concentrated from stations in the Gulf of Mexico, a barrier island pass and a hypersaline lagoon (Laguna Madre), and added to cultures of potential phytoplankton hosts. By following changes in in-vivo fluorescence over time it was possible to isolate several viruses that were pathogens to a variety of marine phytoplankton, including a prasinophyte (Micromonas pusilla), a pennate diatom (likely Navicula sp.), a centric diatom (of unknown taxa), and a chroococcoid cyanobacterium (Synechococcus sp.). As well, we observed changes in fluorescence in cultures of a cryptophyte (Rhodomonas sp.) and a chlorophyte (Nannochloropsis oculata) which were consistent with the presence of viral pathogens. Although pathogens were isolated from all stations, all the pathogens were not isolated from every station. Filterability studies on the viruses infecting Micromonas and Navicula showed that the viruses were consistently infective after filtration through polycarbonate and glass-fiber filters, but were affected by most other filter types. Establishment of phytoplankton/pathogen systems will be important in elucidating the affect that viruses have on primary producers in aquatic systems. [TOP OF PAGE]
Circular dichroism studies of salt- and alcohol- induced conformational changes in cyanophage S-2L DNA which contains amino 2 adenine instead of adenine. Vorlickova,M., Hejtmankova,I., Kypr,J. (1991). J Biomol Struct Dyn 9:81-85. DNA molecules containing AT pairs exhibit cesium cation specific conformational behavior. This specificity is shown to be cancelled with the title DNA, which not only concerns its conformational alterations in high-salt aqueous solutions but also the B-to-A transition induced by ethanol. S-2L DNA easily adopts the A-conformation in the presence of millimolar concentrations of CsCl which completely destabilize the A-conformation in calf thymus DNA. The present results demonstrate that the specific effects of cesium cations on DNA are connected with their binding to the AT pairs in the DNA minor groove. [TOP OF PAGE]
A new temperate cyanophage NP-1T lysogenizing cyanobacterial cultures belonging to the genera Nostoc and Plectonema. Muradov,M., Cherkasov,G.V., Akhmedova,D.U., Khalmuradov,A.G. (1990). Mikrobiologija (Microbiologiia) 59:1038-1045. A new temperate cyanophage NP-1T growing on Nostoc and Plectonema cyanobacterial cultures is described. Cyanophages of the NP type are widespread in Uzbekistan water basins. The cyanophage has a hexagonal head on a plane with a distance of 78 nm between the facets, but lacks a distinctly differentiated tail. Its adsorption takes 2.5 to 3 h. The lytic cycle takes 30 h with 14 h for the latent period. The phage yield is about 350 particles per infected cell. The DNA has 72 mol.% G + C. The mean contour length is 14.4 .mu.m and the molecular mass of DNA calculated in terms of its length is 28 MDa. When the cyanophage interacts with the host culture, lysogenic clones resistant to the cyanophage appear. [TOP OF PAGE]
Comparative study of NP-IT cyanophages, which lysogenize nitrogen-fixing bacteria of the genera Nostoc and Pleconema (Russian?). Muradov,M.M., Cherkasova,G.V., Akhmedova,D.U., Kamilova,F.D., Mukhamedov,R.S., Abdukarimov,A.A., Khalmuradov,A.G. (1990). Mikrobiologija (Microbiologiia) 59:819-826. Comparative characteristics of NP-1T cyanophages causing lysis of nitrogen-fixing Nostoc and Plectonema cultures.The strain specificit