Bacteriophage Ecology Group
Aquatic Virus 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
  1. Association of a bacteriophage with virulence in Vibrio harveyi. Austin,B., Pride,A.C., Rhodie,G.A. (2003). Journal of Fish Diseases 26:55-58. The virulence of Vibrio harveyi, which is a serious pathogen of penaeids (Karunasagar, Pai, Malathi & Karunasagar 1994; Pizzuto & Hirst 1995; Alvarez, Austin, Alvarez & Reyes 1998) and finfish (Kraxberger-Beatty, McGarey, Grier & Lim 1990; Ishimaru & Muroga 1997), has been associated with possession of double haemolysin genes (Zhang, Meaden & Austin 2001). The study seeks to investigate a possible relationship between virulence and the previously described bacteriophage of V. harveyi (Oakey & Owens 2000). The bacteriophage, which has been determined to have an icosahedral head and rigid tail and to contain double stranded linear DNA, has been presumptively assigned to the genus Myovirus (Oakey & Owens 2000). [TOP OF PAGE]

  2. Direct estimates of the contribution of viral lysis and microzooplankton grazing to the decline of a Micromonas spp. population. Evans,C., Archer,S.D., Jacquet,S., Wilson,W.H. (2003). Aquat. Microb. Ecol. 30:207-219. During a mesocosm study in Raunefjorden, Norway, a Micromonas spp. population, initially showing exponential net growth, dramatically declined after Day 4 of the experiment. Using a modification of the dilution approach originally developed to quantify grazing by microzooplankton on phytoplankton, it was possible to partition the mortality of Micromonas spp. between grazing and viral lysis on Days 5, 6 and 7 during the population decline. Parallel dilution experiments were carried out in which 0.2 µm- and 10 kDa-filtered water was used as the diluents. In this way, gradients of grazing pressure (0.2 µm series) and grazing pressure + viral concentration (10 kDa series) were produced. Model 1 linear regression of the fraction of whole water versus the apparent growth rate of chlorophyll a and Micromonas spp. provided an estimate of mortality in the 0.2 µm and 10 kDa dilution series. On Days 5, 6 and 7, the slopes of the linear regressions of 0.2 µm and 10 kDa dilution series were significantly different at p = 0.083, 0.001 and 0.093 respectively. From the differences in slope between the series, estimates of viral mortality amounted to a turnover rate of the Micromonas spp. standing stocks of 10, 25 and 9% d(-1). This compares to a turnover rate by the microzooplankton of 48, 26 and 23% d(-1). On all 3 d the combined viral lysis and grazing mortality exceeded estimates of the potential production of Micromonas spp., in part accounting for the population decline. This study demonstrates that the dilution approach can be adapted to directly determine virus-induced mortality rates of specific phytoplankton. However, further work is required to determine how the specificity of viral infection and variety of viral infection cycles affect the results of this modified dilution approach when applied to other phytoplankton taxa and communities. [TOP OF PAGE]

  3. 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]

  4. The complete sequence of marine bacteriophage VpV262 infecting Vibrio parahaemolyticus indicates that an ancestral component of a T7 viral supergroup is widespread in the marine environment. Hardies,S.C., Comeau,A.M., Serwer,P., Suttle,C.A. (2003). Virology 310:359-371. The 46,012-bp sequence of the marine bacteriophage VpV262 infecting the bacterium Vibrio parahaemolyticus is reported. The VpV262 sequence reveals that it is a distant relative of marine Roseophage SIO1, and an even more distant relative of coliphage T7. VpV262 and SIO1 appear to represent a widespread marine phage group that lacks an RNA polymerase gene and is ancestral to the T7-like phages. We propose that this group together with the T7-like phages be designated as the T 7 supergroup. The ancestral head structure gene module for the T7 supergroup was reconstructed by using sensitive biased Psi-blast searches supplemented by statistical support derived from gene order. In the early and replicative segments, these phages have participated in extensive interchange with the viral gene pool. VpV262 carries a different replicative module than SIO1 and the T7-like phages. [TOP OF PAGE]

  5. The vertical distribution and diversity of marine bacteriophage at a station off Southern California. Jiang,S., Fu,W., Chu,W., Fuhrman,J.A. (2003). Microb. Ecol. 45:399-410. Sixty-two bacteriophages were isolated on eight indigenous bacteria from a Pacific Ocean station spanning 887-m vertical depth, on two occasions between 1999 and 2000. On the basis of 16S rRNA sequences, six hosts were tentatively identified to be in the genus Vibrio and the other two were closely related to Altermonas macleodii (W9a) and Pseudoalteromonas spp. (W13a). Restriction fragment length polymorphism (RFLP) analysis of phage genomes using AccI and HapI showed that 16 phages infecting host C4a (Vibrio) displayed 14 unique RFLP patterns. However, identical phages infecting host C4b, C6a, and C6b (all Vibrio) were obtained from both the surface layer and the hypoxic zone at 850 m. Most phage isolates from the second year had a different RFLP pattern but shared genetic similarity to the phages infecting the same host from the previous year based on a hybridization study using phage genome probes. Cluster analysis of RFLP patterns and hybridization results also indicated that phages infecting the same or genetically related hosts, in general, shared higher degrees of homology in spite of the diverse RFLP patterns. Pulsed field gel electrophoresis (PFGE) analysis of native viral genomes indicated a range in genome size from less than 40 to 200 kb, and the dominant band shifted up by about 5-10 kb in the deep samples compared to the shallow ones. Hybridization of phage genome probes with total viral community DNA from various depths suggests these isolates, or at least some of their genes, represent a detectable portion of the natural viral community and were distributed throughout the water column. Thus, the results of this study demonstrated that the genetic diversity of bacteriophage in the ocean is far greater than that of their bacterial hosts. However, host range may have contributed to the evolution of the diverse phage population in the marine environment. [TOP OF PAGE]

  6. 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]

  7. 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]

  8. 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]

  9. [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]

  10. [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]

  11. Virus-induced transfer of organic carbon between marine bacteria in a model community. Middelboe,M., Riemann,L., Steward,G.L., Hansen,V., Nybroe,O. (2003). Aquat. Microb. Ecol. ???:??? [TOP OF PAGE]

  12. Spatial distribution of viruses and relation to bacterial activity in a coastal marine sediment. Middelboe,M., Glud,R.N., Finster,K. (2003). Limnol. Oceanogr. ???:??? [TOP OF PAGE]

  13. Genomes of two lysogenic marine phage that infect Vibrio paraheamolyticus. Rohwer,F., Seguritan,V., Feng,I., Segall,A. (2003). [TOP OF PAGE]

  14. Virus succession observed during an Emiliania huxleyi bloom. Schroeder,D., Oke,J., Malin,G., Wilson,W.H. (2003). Appl. Environ. Microbiol. 69:2484-2490. Denaturing gradient gel electrophoresis was used as a molecular tool to determine the diversity and to monitor population dynamics of viruses that infect the globally important coccolithophorid Emiliania huxleyi. We exploited variations in the major capsid protein gene from E. huxleyi-specific viruses to monitor their genetic diversity during an E. huxleyi bloom in a mesocosm experiment off western Norway. We reveal that, despite the presence of several virus genotypes at the start of an E. huxleyi bloom, only a few virus genotypes eventually go on to kill the bloom. [TOP OF PAGE]

  15. 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]

  16. Wide geographic distribution of bacteriophages that lyse the same indigenous freshwater isolate (Sphingomonas sp. strain B18). Wolf,A., Wiese,J., Jost,G., Witzel,K.P. (2003). Appl. Environ. Microbiol. 69:2395-2398. An indigenous freshwater bacterium (Sphingomonas sp. strain B18) from Lake Plubetasee (Schleswig-Holstein, Germany) was used to isolate 44 phages from 13 very different freshwater and brackish habitats in distant geographic areas. This bacterial strain was very sensitive to a broad spectrum of phages from different aquatic environments. Phages isolated from geographically distant aquatic habitats, but also those from the same sample, were diverse with respect to morphology and restriction pattern. Some phages were widely distributed, while different types coexisted in the same sample. It was concluded that phages could be a major factor in shaping the structure of bacterial communities and maintaining a high bacterial diversity. [TOP OF PAGE]

  17. Fundamental changes in light scattering associated with infection of marine bacteria by bacteriophage. Balch,W.M., Vaughn,J.M., Novotny,J.F., Drapeau,D.T., Goes,J.I., Booth,E., Lapierre,J.M., Vining,C.L., Ashe,A., Vaughn,J.J. (2002). Limnol. Oceanogr. 47:1554-1561. Bacteria and phytoplankton are key determinants of the ocean's inherent optical properties. Despite their high abundance, marine viruses have generally been thought to play a minor role in ocean optics because of their small scattering cross-sections. Nevertheless, the role of specific viral infection on the optical properties of bacteria and phytoplankton has remained unknown (i.e., as viruses disrupt micron-sized host cells to produce submicron cell debris). Here, we used laboratory and mesocosm cultures of marine bacteria for virus infection experiments in which growth conditions and host-virus specificity were controlled. We report that the chief optical impact of viruses is associated with infection and lysis of their hosts. We quantitatively describe, for the first time, two optical changes associated with infection and lysis of marine bacteria by bacteriophage: (1) rapid, strong shifts in the magnitude and shape of the optical volume scattering function and (2) rapid production of colored dissolved organic material. Qualitatively, these changes result in nearly complete clearing of turbid host bacterial suspensions. Although some optical differences would be expected between infection of bacteria in laboratory cultures versus field populations (mainly because of differences in cell size), these results are applicable to the field, especially for dense host suspensions such as in blooms. Even in nonbloom situations, as long as the host bacteria contribute a significant amount of the total particle backscattering, we expect that virus-induced backscattering changes would be detectable by use of satellite or aircraft remote-sensing techniques. [TOP OF PAGE]

  18. Genomic analysis of uncultured marine viral communities. Breitbart,M., Salamon,P., Andresen,B., Mahaffy,J.M., Segall,A.M., Mead,D., Azam,F., Rohwer,F. (2002). Proc. Natl. Acad. Sci. USA 99:14250-14255. Viruses are the most common biological entities in the oceans by an order of magnitude. However, very little is known about their diversity. Here we report a genomic analysis of two uncultured marine viral communities. Over 65% of the sequences were not significantly similar to previously reported sequences, suggesting that much of the diversity is previously uncharacterized. The most common significant hits among the known sequences were to viruses. The viral hits included sequences from all of the major families of dsDNA tailed phages, as well as some algal viruses. Several independent mathematical models based on the observed number of contigs predicted that the most abundant viral genome comprised 2-3% of the total population in both communities, which was estimated to contain between 374 and 7,114 viral types. Overall, diversity of the viral communities was extremely high. The results also showed that it would be possible to sequence the entire genome of an uncultured marine viral community. [TOP OF PAGE]

  19. On the stability properties of a stochastic model for phage-bacteria interaction in open marine environment. Carletti,M. (2002). Math. Biosci. 175:117-131. In this paper we extend the deterministic model for the epidemics induced by virulent phages on bacteria in marine environment introduced by Beretta and Kuang [Math. Biosci. 149 (1998) 57], allowing random fluctuations around the positive equilibrium. The stochastic stability properties of the model are investigated both analytically and numerically suggesting that the deterministic model is robust with respect to stochastic perturbations. [TOP OF PAGE]

  20. 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]

  21. Occurrence and levels of indicator bacteriophages in bathing waters throughout Europe. Contreras-Coll,N., Lucena,F., Mooijman,K., Havelaar,A., Pierz,V., Boque,M., Gawler,A., Holler,C., Lambiri,M., Mirolo,G., Moreno,B., Niemi,M., Sommer,R., Valentin,B., Wiedenmann,A., Young,V., Jofre,J. (2002). Water Res. 36:4963-4974. Somatic coliphages, F-specific RNA bacteriophages, bacteriophages infecting Bacteroides fragilis, Escherichia coli and enterococci were counted in bathing waters in the late spring and summer. We tested fresh and marine bathing waters from North, South, East and West Europe expected to contain between 100 and 500 E. coli per 100 ml, although wider ranges were sometimes found. Bacteriophages were counted after concentration, since a preliminary study proved that this step was necessary to obtain positive counts. During monitoring, a first-line quality control with reference materials for bacteria and bacteriophages was performed by all the laboratories participating in the study. The same microbes were also counted in raw sewage samples from various areas in Europe, where the bacterial indicators and the three groups of bacteriophages were detected in roughly the same numbers. All groups of bacteriophages were detected in both fresh and marine bathing waters throughout Europe. Reliable and complete results from 147 samples showed that for log-transformed values, E. coli and bacteriophages were slightly correlated. However, the slope of the regression line changed according to E. coli concentration and the correlation diminished when this concentration was close to zero per 100 ml. The ratios between E. coli and phages in bathing waters differed significantly from those in sewage. The relative amounts of bacteriophages, mainly somatic coliphages and phages infecting Bact. fragilis RYC2056, increased in bathing waters with low E. coli concentration, especially in seawater samples containing < 100 E. coli per 100 ml. The relationship of bacteriophages with respect to enterococci paralleled that of bacteriophages with respect to E. coli. Somatic coliphages and bacteriophages infecting Bact. fragilis are useful to predict the presence of some pathogens with the same origin as present bacterial indicators but with higher survival rates. [TOP OF PAGE]

  22. High control of bacterial production by viruses in a eutrophic oxbow lake. Fischer,U.R., Velimirov,B. (2002). Aquat. Microb. Ecol. 27:1-12. The aim of the study was to test the hypothesis that the magnitude of viral control on bacterial production in a eutrophic oxbow lake of the River Danube would be higher than all average values reported so far in the literature. This assumption was based on the findings of low grazing of heterotrophic nanoflagellates (HNF) in this system, accounting on average for 5% of the bacterial mortality. Several approaches (viral decay method, estimation of the frequency of infected bacterial cells) to determine viral control of bacterial production were applied on a comparative basis. All system-specific parameters necessary to describe virus-bacteria interactions (burst size, bacterial production, contact rates) were monitored simultaneously. The average viral control of bacterial production determined by the different approaches was similar, ranging from 55.7 to 62.7 %, and prevailing over HNF grazing by a factor of more than 11. For individual events, however, we observed large variations between the methods, indicating that the use of one single method is not reliable to decide whether a detected trend is representative of a specific system. We discuss error sources of the applied methods and mathematical models, and accounted for them when calculating the contribution of viruses to bacterial mortality. We demonstrated that viruses could control more than 100 % of the bacterial production in the Alte Donau, which implies that occasionally up to 1.6 % h-1 of the bacterial standing stock was removed from the water column. High bacterial mortality due to viruses indicated that a large amount of dissolved organic carbon might be recycled from bacteria by phage-induced cell lysis. On average 15.2 mu g C l-1 d-1, corresponding to some 46 % of the bacterial secondary production (BSP), was released into the water column due to viral lysis of bacterial cells and again became available for microheterotrophic consumption. [TOP OF PAGE]

  23. 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]

  24. Sunlight inactivation of human enteric viruses and fecal bacteria. Fujioka,R.S., Yoneyama,B.S. (2002). Water Sci. Technol. 46:291-295. Three human enteric viruses (poliovirus, echovirus, coxsackievirus) suspended in seawater or buffer were stable for 6 hr in the absence of sunlight but were inactivated at the same rate in the presence of sunlight. Under summer sunlight conditions, at least 3 logs of these viruses were inactivated by one-hit kinetics while under winter sunlight conditions only 1 log of these viruses was inactivated by two-hit kinetics. Under these same conditions, 6 logs of E. coli were inactivated within 1 hr by one-hit kinetics under summer and winter conditions. In comparison, E. faecalis was inactivated by two-hit kinetics and only 2.5 logs of inactivation were observed after 4 hr of exposure to winter sunlight. Since human enteric viruses are considerably more resistant to sunlight inactivation than E. coli and moderately more resistant than E. faecalis, marine recreational water quality standards should be based on concentrations of enterococci and not on coliform bacteria. Since the mechanism and rate of inactivation of coliphage and human enteric viruses are similar, coliphages appear to be the best indicator for the presence of human enteric viruses in recreational waters, especially coastal waters where abundant sunshine is available. [TOP OF PAGE]

  25. Bacteriophage replication and reactivation in stationary phase hosts. Gallimore,W.H., Burgess,J.M., Kokjohn,T.A. (2002). Research Signpost 6:467-476. Bacteriophage dynamics in stationary phase or stressed bacterial hosts are poorly understood. Using one-step growth experiments we have demonstrated that stationary phase does not constitute an absolute block to phage multiplication, although latent periods are extended and burst sizes decreased substantially compared to exponential phase infections. Using infectious center assays to quantify lysogen responses to DNA damage revealed that while there was a range of sensitivity to ultraviolet (UV) radiation, no prophages were induced by sunlight exposure. Comparing the capacity of exponential phase and stationary phase cells to resist UV irradiation and reactivate UV-damaged phage revealed that cells maintained in the stationary phase at the time of infection expressed significantly higher levels of DNA repair. Photoreactivation experiments in stationary phase hosts revealed that light-mediated reversal of phage DNA damage definitely occurred in stationary phase bacterial hosts. Our experiments demonstrate that many bacteriophages multiply actively and are competent to reverse DNA damage in post exponential phase host cells. In order to establish the scope and significance of bacteriophages to aquatic ecosystem ecology a more complete understanding of virus dynamics in both growing and stationary phase hosts is essential. [TOP OF PAGE]

  26. 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]

  27. [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]

  28. Viral distribution and activity in Antarctic waters. Guixa-Boixereu,N., Vaque,D., Gasol,J.M., Sanchez-Camara,J., Pedros-Alio,C. (2002). Deep-Sea Research II 49:827-845. Variability in abundance of virus-like particles (VLP), VLP decay rates and prokaryotic mortality due to viral infection were determined in three Antarctic areas: Bellingshausen Sea, Bransfield Strait and Gerlache Strait, during December 1995 and February 1996. VLP abundance showed very small spatial variability in the three areas (7 x 106-2 x 107 VLP ml-1). VLP abundance, on the other hand, decreased one order of magnitude from the surface to the bottom, in two stations where deep vertical profiles were sampled. Low seasonal variability in VLP abundance was found when comparing each area separately. Diel VLP variability was also very low. VLP abundance showed the lowest values when solar irradiation was maximal, in two of the three stations where diel cycles were examined. Viral decay rates (VDR) were determined using KCN in two kinds of experiments. Type 1 experiments were performed in 6 stations to determine viral decay. Type 2 experiments were carried out in 2 stations to examine the influence of temperature and organic matter concentration on viral decay. VDR was not influenced by these parameters. Prokaryotic mortality due to viral infection was always higher than that due to bacterivores in the stations where both factors of prokaryotic mortality were measured. Viral infection accounted for all the prokaryotic heterotrophic production in Bellingshausen Sea and Gerlache Strait and for half of the prokaryotic heterotrophic production in Bransfield Strait. These high values of prokaryotic mortality due to viral infection are difficult to reconcile in nature, and more work is necessary to determine the mechanisms involved in the disappearance of viruses. [TOP OF PAGE]

  29. 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]

  30. Flow cytometric analysis of an Emiliania huxleyi bloom terminated by viral infection. Jacquet,S., Heldal,M., Iglesias-Rodriguez,D., Larsen,A., Wilson,W.H. (2002). Aquat. Microb. Ecol. 27:111-124. During a field mesocosm experiment conducted in coastal waters off western Norway, 11 m(3) enclosures were filled with unfiltered seawater and enriched daily with different nitrate and phosphate concentrations in order to induce a bloom of the coccolithophorid Emiliana huxleyi under different nutrient regimes. Flow cytometry (FCM) analysis was performed 5 times d(-1) in order to follow the initiation, development and termination of the bloom as well as the production of large virus-like particles (LVLPs) identified as E. huxleyi viruses (EhV). EhV production was observed first in the enclosure where N was in excess, and P limitation induced a lower burst size compared to nitrate-replete enclosures. These observations suggest a critical role for both P and N in E. huxleyi-EhV interactions. Concomitant to EhV production, a shift was observed between the original population (coccolith-bearing cells) towards a population characterized by the same chlorophyll a (chl a) fluorescence but with lower right angle light scatter values. This population is likely to correspond to either senescent cells losing their coccoliths or cells characterized by a lower production of coccoliths possibly due to viral infection. At the end of experiment, a significant proportion of E. huxleyi had survived after the end of the bloom. This suggests either the presence of a resistant form of the coccolithophorid or a change in the dominance of different host and/or viral strains during the bloom. A periodical pattern in virus production was recorded with virus number decreasing during the second part of the day suggesting that virus production may be synchronized to the daily light cycle. Our results provide new insights towards the understanding of the relationship between a key marine species and its specific virus. [TOP OF PAGE]

  31. Degree of ultraviolet radiation damage and repair capabilities are related to G+C content in marine vibriophages. Kellogg,C.A., Paul,J.H. (2002). Aquat. Microb. Ecol. 27:13-20. A key issue in the ecology of viruses in the marine environment is the rate of viral production and decay. The ultraviolet (UV) radiation in sunlight has been found to cause loss of infectivity in marine bacteriophages at rates nearly equal to all other decay mechanisms combined. There are 2 main host-mediated mechanisms that can repair UV-damaged phage DNA: photoreactivation and excision repair. Both these mechanisms were investigated in 2 marine Vibrio parahaemolyticus hosts as they catalyzed the reactivation of 7 phages. Photoreactivation was the dominant repair mode in all but one case. A significant correlation was found between G+C content of the phage DNAs (16 to 70 %) and degree of DNA damage (r = 0.955), indicating a strong relationship between the number of thymine dimer targets and the capability to photoreactive DNA damage. Evolution of high G+C content may be a strategy for protection from UV damage in marine phages. [TOP OF PAGE]

  32. Viruses causing lysis of the toxic bloom-forming alga, Heterosigma akashiwo (Raphidophyceae), are widespread in coastal sediments of British Columbia, Canada. Lawrence,J.E., Chan,A.M., Suttle,C.A. (2002). Limnol. Oceanogr. 47:545-550. Viruses that infect and cause lysis of the toxic alga Heterosigma akashiwo are abundant and widespread in the Strait of Georgia, Canada, and adjacent inlets during the summer months when blooms of this alga occur. Because viruses are subjected to many mechanisms of removal and their host is intermittently dormant, the persistence of viruses may be dependent on environmental reservoirs. We extracted pore water from sediments collected in the Strait of Georgia and screened for the presence of infectious agents that cause lysis of H. akashiwo. Lytic agents were widespread throughout the study region, being detected in 17 of 20 sites surveyed. Lytic agents were present in sediments ranging from highly organic to clay-rich and were retrieved from cores taken at water depths of 25-285 m. The highest concentration of lytic agents was found at the sediment-water interface; however, lytic agents were found as deep as 40 cm below the sediment-water interface. Examination of agents isolated from various sites revealed virus-like particles similar to50 nm in diameter. These are similar to other virus-like particles that have been isolated that infect this alga. This suggests that the most abundant lytic agents in the sediments are viruses and that these viruses may be long-lived once buried in the sediments. The widespread presence of viral-size lytic agents that infect H. akashiwo is consistent with viral infection being a mortality agent of this alga in the overlying waters and suggests that they may play in important role in regulating their population dynamics. [TOP OF PAGE]

  33. 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]

  34. Regeneration of dissolved organic matter by viral lysis in marine microbial communities. Middelboe,M., Lyck,P.G. (2002). Aquat. Microb. Ecol. 27:187-194. The influence of viruses on bacterial net growth and respiration was investigated in batch cultures with natural assemblages of marine bacterioplankton, which were manipulated with respect to abundance of natural virioplankton. In 1 set of cultures (-virus), a virus-free water sample (0.02 mu m filtered) was inoculated with a bacterioplankton concentrate, and in a parallel set of cultures (control) a virus-containing water sample (0.2 mu m filtered) was inoculated with the bacterioplankton concentrate. The 0.02 mu m filtration procedure reduced viral abundance by 62 to 92% in the -virus cultures relative to the parallel control cultures with the natural density of viruses (i.e. the fraction of natural viruses < 0.2 mu m). This approach allowed us to examine the effects of reduced viral densities on the production of natural assemblages of bacteria and viruses and on the distribution of added 3H-thymidine into size fractions (the bacterial size fraction, viral size fraction, dissolved size fraction and respired fraction). The results showed significantly higher bacterial net growth and growth efficiency in cultures with a reduced abundance of viruses relative to control cultures with natural viral abundance, and indicated viral regulation of bacterial abundance in the control cultures. We suggest that viral lysis significantly affected the bacterial carbon cycling in the cultures by liberating a fraction of the organic matter already taken up by the bacteria, thus stimulating recycling of bacterial carbon and reducing the net bacterial production. The implications of such regeneration of dissolved organic matter by viral lysis for pelagic carbon cycling and for measurements of bacterial production are discussed. [TOP OF PAGE]

  35. Virus-like particle analysis in a seston-rich coastal pond using transmission electron microscopy. Montanie,H., Hartmann,H.J., Crottereau,C., Trichet,C. (2002). Aquat. Microb. Ecol. 28:105-115. A method was developed to analyse virus-like particles (VLPs) in seston-rich waters and to quantify their dynamics in a coastal marsh of the Bay of Biscay, French Atlantic coast. The method combined clarification and concentration steps with electron microscopy to obtain information on particle abundance, type and size distribution (e.g. presence of tailed phages, Fuselloviridae, etc.). The mean recovery rates of T2-phages using this method were 71 to 79%, higher than other published rates. The transmission electron microscopy (TEM) counts were validated with T2 plaque lysis assay and epifluorescent (DAPI-stained) particle counting: the TEM method was valid for environmental particle concentrations above 1 to 2 x 106 VLP ml-1; TEM counts were lower than T2-plaque counts (TEM/lysis median = 0.293) but higher than DAPI counts (TEM/DAPI median = 2.39). The method was used to evaluate the coupling between viral and bacterial dynamics in a marsh pond during 2 months. The VLP abundance varied from 1 to 30 x 106 ml super(-1) and the viral population was dominated by small particles (20 to 64 nm). Tailed phages, identified as bacteriophages, were always less abundant than non-tailed VLPs (4 to 23% of total virus), yet their dynamics were better linked with bacterial development than those of total virus. Our results demonstrate that the best way to characterise bacterial lysis from virus in seston-rich coastal environments would be to study the dynamics of tailed phages and virus size-classes rather than the commonly applied total VLPs. [TOP OF PAGE]

  36. 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]

  37. 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]

  38. A filterable lytic agent obtained from a red tide bloom that caused lysis of Karenia brevis (Gymnodinum breve) cultures. Paul,J.H., Houchin,L., Griffin,D., Slifko,T., Guo,M., Richardson,B., Steidinger,K. (2002). Aquat. Microb. Ecol. 27:21-27. A filterable lytic agent (FLA) was obtained from seawater in the southeastern Gulf of Mexico during a red tide bloom that caused lysis of Karenia brevis (formerly Gymnodinium breve) Piney Island. This agent was obtained from <0.2 mu m filtrates that were concentrated by ultrafiltration using a 100 kDa filter. The FLA was propagated by passage on K. brevis cultures, and the filtered supernatants of such cultures resulted in K. brevis lysis when added to such cultures. The lytic activity was lost upon heating to 65 degree C or by 0.02 mu m filtration. Epifluorescence and transmission electron microscopy (TEM) of supernatants of K. brevis cultures treated with the lytic agent indicated a high abundance of viral particles (4 x 109 to 7 x 109 virus-like particles [VLPs] ml-1) compared to control cultures ( similar to 107 ml-1). However, viral particles were seldom found in TEM photomicrograph thin sections of lysing K. brevis cells. Although a virus specific for K. brevis may have been the FLA, other explanations such as filterable bacteria or bacteriophages specific for bacteria associated with the K. brevis cultures cannot be discounted. [TOP OF PAGE]

  39. Spatial stability of bacterial and viral community compositions in Danish coastal waters as depicted by DNA fingerprinting techniques. Riemann,L., Middelboe,M. (2002). Aquat. Microb. Ecol. 27:219-232. [TOP OF PAGE]

  40. Viral lysis of marine bacterioplankton: Potential implications for organic matter cycling and bacterial clonal composition. Riemann,L., Middelboe,M. (2002). Ophelia 56:57-68. [TOP OF PAGE]

  41. Coccolithovirus (Phycodnaviridae): characterisation of a new large dsDNA algal virus that infects Emiliania huxleyi. Schroeder,D., Oke,J., Malin,G., Wilson,W.H. (2002). Arch Virol 147:1685-1698. Emiliania huxleyi-specific viruses (EhV) were isolated from E. huxleyi blooms off the coast of Plymouth, UK, in July 1999 and July/August 2001, and from an E. huxleyi bloom induced during a mesocosm experiment in a fjord off Bergen, Norway, during June 2000. Transmission electron microscopy revealed that all 10 virus isolates are 170-200 nm in diameter with an icosahedral symmetry. Their density is approximately 1.2 in CsCl gradients and they have large double stranded DNA genomes approximately 410 kb in size. Phylogenetic analysis of the DNA polymerase genes of these viruses suggests that EhV belongs to a new genus within the family of algal viruses, Phycodnaviridae. We propose to name this new virus genus Coccolithovirus. Differences within members of the Coccolithovirus were elucidated by host range analysis of the virus isolates and sequence analysis of a gene fragment encoding part of their putative major capsid protein. All 10 virus isolates within this new genus only infected E. huxleyi strains that have previously been shown to exhibit low dimethylsulphoniopropionate lyase (DMSP-lyase) activity (CCMP1516, CCMP374 and L), while E. huxleyi strains with high DMSP-lyase activity (CCMP373 and CCMP379) were resistant to infection. [TOP OF PAGE]

  42. Sequence analysis of marine virus communities reveals groups of related algal viruses are widely distributed in nature. Short,S.M., Suttle,C.A. (2002). Appl. Environ. Microbiol. 68:1290-1296. Algal-virus-specific PCR primers were used to amplify DNA polymerase (pol) gene fragments from geographically isolated natural virus communities. Natural algal virus communities were obtained from coastal sites in the Pacific Ocean in British Columbia, Canada, and the Southern Ocean near the Antarctic peninsula. Genetic fingerprints of algal virus communities were generated using denaturing gradient gel electrophoresis (DGGE). Sequencing efforts recovered 33 sequences from the gradient gel. Of the 33 sequences examined, 25 encoded a conserved amino acid motif indicating that the sequences were pol gene fragments. Furthermore, the 25 pol sequences were related to pol gene fragments from known algal viruses. In addition, similar virus sequences (>98% sequence identity) were recovered from British Columbia and Antarctica. Results from this study demonstrate that DGGE with degenerate primers can be used to qualitatively fingerprint and assess genetic diversity in specific subsets of natural virus communities and that closely related viruses occur in distant geographic locations. DGGE is a powerful tool for genetically fingerprinting natural virus communities and may be used to examine how specific components of virus communities respond to experimental manipulations. [TOP OF PAGE]

  43. [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]

  44. [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]

  45. Reconsidering transmission electron microscopy based estimates of viral infection of bacterio-plankton using conversion factors derived from natural communities. Weinbauer,M.G., Winter,C., Hofle,M.G. (2002). Aquat. Microb. Ecol. 27:103-110. The frequency of virus infected bacterial cells (FIC) was estimated in surface waters of the Mediterranean Sea, the Baltic Sea and the North Sea using the frequency of visibly infected cells (FVIC) as determined by transmission electron microscopy (TEM) and published average conversion factors (average 5.42, range 3.7 to 7.14) to relate FVIC to FIC. A virus dilution approach was used to obtain an independent estimation of FIC in bacterioplankton, and we provide evidence for the reliability of this approach. Across all investigated environments, FIC ranged from 2.4 to 43.4 %. FIC data using both approaches were well correlated; however, the values were higher using the virus dilution approach, This indicates that the TEM approach has the potential to reveal spatiotemporal trends of viral infection; however, it may underestimate the significance of viral infection of bacteria when average conversion factors are used. Using data from the virus dilution approach and the TEM approach, we calculated new conversion factors for relating FVIC to FIC (average 7.11, range 4.34 to 10.78). Virally caused mortality of bacteria estimated from published FVIC data of marine and freshwater systems and using the new conversion factors ranged from not detectable to 129 %, thus confirming that viral infection is a significant and spatiotemporally variable cause of bacterial cell death. [TOP OF PAGE]

  46. Pseudoalteromonas spp. phages, a significant group of marine bacteriophages in the North Sea. Wichels,A., Gerdts,G., Schuett,C. (2002). Aquat. Microb. Ecol. 27:233-239. The occurrence and distribution of specific bacteriophages of marine Pseudoalteromonas spp. in the North Sea (North Sea phages) and their genetic relationship to several previously isolated marine phage species from waters of the Helgoland Roads (German Bight, Helgoland phages) were investigated. During 3 cruises from the Elbe estuary to western Norwegian waters, phages were concentrated by ultrafiltration. Detection and isolation of North Sea phages were performed by plaque assay, with 70 host bacteria of the genus Pseudoalteromonas. The genetic relationship between North Sea phages from different stations and Helgoland phages, formerly described as Pseudoalteromonas spp. phages, was assessed by DNA-DNA hybridization. DNA probes were prepared using whole phage DNA derived from 13 Helgoland phages. This approach provides the first information on the distribution of specific Pseudoalteromonas spp. phage-host systems (PHS) in the North Sea. The occurrence of Pseudoalteromonas spp. phages, which are specific for the tested Pseudoalteromonas spp. host bacteria, was restricted to a narrow geographical region of the German Bight between 53 degree 30' and 57 degree 00' N latitude. Most of the previously isolated Helgoland phages were highly host specific (54%), whereas this was true for only some of the 39 North Sea phages (16%). The most common Pseudoalteromonas spp. phage species found in the North Sea belong to the virus family Siphoviridae (species H103/1). Several phage strains within this phage species displayed different host sensitivity patterns. [TOP OF PAGE]

  47. Virus dynamics in a coccolithophore-dominated bloom in the North Sea. Wilson,W.H., Tarran,G., Zubkoy,M.V. (2002). Deep Sea Research Part II: Tropical Studies in Oceanography 49:2951-2963. We used analytical flow cytometry (AFC) to determine virus concentrations through vertical profiles in a coccolithophore-dominated bloom in the northern North Sea during June 1999. We present the first high-intensity sampling data of viruses from a lagrangian survey to gain a unique insight into the temporal and spatial dynamics of viruses in an open-water sight. Virus abundances ranged from 2.6×10(5) to 5.4×10(6)ml(-1), which is within the range expected for open-water environments. The highest concentrations were invariably observed in surface waters. During the lagrangian experiment there was a net decrease in virus numbers, suggesting that they were actively infecting hosts. Large viruses could be easily discriminated from small viruses since there was at least an order of magnitude difference in their AFC side-scatter values. Large viruses, assumed to infect DMS-producing algae, did not appear to influence DMS/DMSP production. It is likely that microzooplankton out-competed viruses for coccolithophore prey/hosts. Lower small virus to bacteria ratios (VBR) were observed in a subsurface layer compared to the more productive surface layers. The subsurface layer was dominated by a species of a-proteobacteria related to the genus Roseobacter, and the low VBR may indicate that viruses were infecting Roseobacter in this layer. Application of AFC is an excellent technique for high-definition sampling of virus communities, although it is recognised that we are working at the limit of detection for many small viruses using currently available nucleic acid stains. [TOP OF PAGE]

  48. Isolation of viruses responsible for the demise of an Emiliania huxleyi bloom in the English Channel. Wilson,W.H., Tarran,G.A., Schroeder,D., Cox,M., Oke,J., Malin,G. (2002). Journal of the Marine Biological Association of the UK 82:369-377. [TOP OF PAGE]

  49. Evolution of lambdoid replication modules. Wrobel,B., Wegrzyn,G. (2002). Virus Genes 24:163-171. Comparison of the putative iteron-binding proteins of lambdoid phages allows us to propose that in the case of lambdoid replication modules, the units on which natural selection acts do not coincide with the open reading frames. Rather, the first replication gene is split into two segments, and its 3' part (corresponding to the C-terminal domain of the iteron-binding protein) forms one unit with the second gene. We also propose from the phylogenetic analysis of phage-encoded homologs of E. coli DnaB and DnaC, that the recombination with the host sequences is not frequent. Accessory ATP-ases for helicase loading (E. coli DnaC homologs) may not be universal replication proteins. Our analysis may suggest that the bacterial helicase loaders might be of phage origin. The comparison of DnaC homologs of enterobacteria and enterobacterial phages supports the experimental data on residues important in interaction with DnaB. We propose that construction of plasmids carrying the replication origins of lambdoid prophages could be useful not only in further research on DNA replication but also on the role of these prophages in shuttling genes for bacterial virulence. The phage replication sequences could be also useful for identification of clinical enterobacterial isolates. [TOP OF PAGE]

  50. 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]

  51. 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]

  52. Microbial population dynamics and diversity during a bloom of the marine coccolithophorid Emiliania huxleyi (Haptophyta). Castberg,T., Larsen,A., Sandaa,R.A., Brussaard,C.P.D., Egge,J.K., Heldal,M., Thyrhaug,R., van Hannen,E.J., Bratbak,G. (2001). Mar. Ecol. Prog. Ser. 221:39-46. Several previous studies have shown that Emiliania huxleyi blooms and terminations have been succeeded by an increase in large virus-like particles (LVLP), strongly suggesting the bloom collapse was caused by viral lysis. However, due to methodological limitations, knowledge of how such blooms affect the rest of the microbial community is limited. In the current study we induced a bloom of E. huxleyi in seawater enclosures and applied methods enabling us to describe the algae, bacteria and virus communities with greater resolution than has been done previously, The development of the dominating algal, viral and bacterial populations in the nutrient-amended seawater enclosures was followed by flow cytometry (FCM). Light microscopy (LM), PCR-denaturing gradient gel electrophoresis (PCR-DGGE) and pulsed-field gel electrophoresis (PFGE) were used to describe the changes in community composition in greater detail. The algal community was dominated by E. huxleyi until termination of the bloom by viral lysis, After bloom termination the additional algal populations present in the enclosures increased in abundance. A marked increase in viruses other than the one infecting E. huxleyi was also observed. Total bacterial number and community composition were also greatly influenced by the bloom and its collapse. [TOP OF PAGE]

  53. 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]

  54. Application of digital image analysis and flow cytometry to enumerate marine viruses stained with SYBR gold. Chen,F., Lu,J.R., Binder,B.J., Liu,Y.C., Hodson,R.E. (2001). Appl. Environ. Microbiol. 67:539-545. A novel nucleic acid stain, SYBR Gold, was used to stain marine viral particles in various types of samples. Viral particles stained with SYBR Gold yielded bright and stable fluorescent signals that could be detected by a cooled charge-coupled device camera or by flow cytometry. The fluorescent signal strength of SYBR Gold-stained viruses was about twice that of SYBR Green I-stained viruses. Digital images of SYBR Gold-stained viral particles were processed to enumerate the concentration of viral particles by using digital image analysis software. Estimates of viral concentration based on digitized images were 1.3 times higher than those based on direct counting by epifluorescence microscopy. Direct epifluorescence counts of SYBR Gold-stained viral particles were in turn about 1.34 times higher than those estimated by the transmission electron microscope method. Bacteriophage lysates stained with SYBR Gold formed a distinct population in flow cytometric signatures. Flow cytometric analysis revealed at least four viral subpopulations for a Lake Erie sample and two subpopulations for a Georgia coastal sample. Flow cytometry-based viral counts for various types of samples averaged 1.1 times higher than direct epifluorescence microscopic counts. The potential application of digital image analysis and flow cytometry for rapid and accurate measurement of viral abundance in aquatic environments is discussed. [TOP OF PAGE]

  55. 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]

  56. Effects of concentrated viral communities on photosynthesis and community composition of co-occurring benthic microalgae and phytoplankton. Hewson,I., O'Neil,J.M., Heil,C.A., Bratbak,G., Dennison,W.C. (2001). Aquat. Microb. Ecol. 25:1-10. Marine viruses have been shown to affect phytoplankton productivity; however, there are no reports on the effect of viruses on benthic microalgae (microphytobenthos). Hence, this study investigated the effects of elevated concentrations of virus-like particles on the photosynthetic physiology and community composition of benthic microalgae and phytoplankton. Virus populations were collected near the sediment surface and concentrated by tangential flow ultrafiltration, and the concentrate was added to benthic and water column samples that were obtained along a eutrophication gradient in the Brisbane River/Moreton Bay estuary, Australia. Photosynthetic and community responses of benthic microalgae, phytoplankton and bacteria were monitored over 7 d in aquaria and in situ. Benthic microalgal communities responded to viral enrichment in both eutrophic and oligotrophic sediments. In eutrophic sediments, Euglenophytes (Euglena sp.) and bacteria decreased in abundance by 20 to 60 and 26 to 66%, respectively, from seawater controls. In oligotrophic sediments, bacteria decreased in abundance by 30 to 42% from seawater controls but the dinoflagellate Gymnodinium sp. increased in abundance by 270 to 3600% from seawater controls, The increased abundance of Gymnodinium sp. may be related to increased availability of dissolved organic matter released from lysed bacteria. Increased (140 to 190% from seawater controls) initial chlorophyll a fluorescence measured with a pulse-amplitude modulated fluorometer was observed in eutrophic benthic microalgal incubations following virus enrichment, consistent with photosystem II damage. Virus enrichment in oligotrophic water significantly stimulated carbon fixation rates, perhaps due to increased nutrient availability by bacterial lysis. The interpretation of data from virus amendment experiments is difficult due to potential interaction with unidentified bioactive compounds within seawater concentrates. However, these results show that viruses are capable of influencing microbial dynamics in sediments. [TOP OF PAGE]

  57. Virus-like particle distribution and abundance in sediments and overlying waters along eutrophication gradients in two subtropical estuaries. Hewson,I., O'Neil,J.M., Fuhrman,J.A., Dennison,W.C. (2001). Limnol. Oceanogr. 46:1734-1746. Viruses are recognized as ubiquitous components of marine ecosystems; however, there has been limited study of viral abundance and its ecological role in sediments. Viral abundance was determined in both the water column and sediments of a eutrophic (Brisbane River/Moreton Bay; 27º25'S, 153º5'E) and oligotrophic (Noosa River; 26º15'S, 153º0'E) estuary in subtropical Queensland, Australia. Viruses, bacteria, and microalgae from both water column and extracted sediment samples were enumerated using SYBR Green I staining and epifluorescence microscopy. Sediment viral abundance ranged from 107 to 109 particles cm-3 of sediment, bacterial abundance ranged from 107 to 108 cells cm-3 of sediment, and microalgal abundance ranged from 104 to 105 cells cm-3 sediment. Pelagic abundances for all microorganisms were 10-1,000-fold lower than sediment abundances. Correlations between viral abundances and suspended solids suggest that viruses sorbed to suspended material in the water column may settle out and contribute to the benthic viral population. Virus production was measured by a time course increase of viral abundance in seawater using a dilution technique. Virus production was highest in eutrophic waters of the Brisbane River, and addition of inorganic nutrients (NO3- + NH4+ + PO4-3 + SiO3) stimulated viral production rates at all stations by 14-52% above ambient, suggesting that inorganic nutrient availability may play a key role in aquatic viral abundance. [TOP OF PAGE]

  58. Seasonal dynamics of viruses in an alpine lake: Importance of filamentous forms. Hofer,J.S., Sommaruga,R. (2001). Aquat. Microb. Ecol. 26:1-11. Viruses are an important component of the planktonic food web in freshwater and marine systems, but most studies have been done in the ocean and in lowland lakes. In this work, the seasonal dynamics and structure of the virioplankton as well as their impact on bacteria during a day/night cycle were studied in an alpine lake located 2417 m above sea level. The abundance of virus-like particles (VLP) was determined at 5 discrete depths (0.5 to 8 m) by direct counts with a TEM in samples collected from May to November 1998 at weekly to bi-weekly intervals. Viruses reached the highest abundances under ice (4.6 X 106 VLP ml-1) with a second maximum in autumn. After ice-break, the VLP abundance decreased to undetectable values (<2 X 104 VLP ml-1) probably because of the negative effect of solar radiation that was negatively correlated with the viral abundance in the upper 2 m of the water column (Spearman rank correlation, rs = -0.773, p < 0.01). The virioplankton was morphologically diverse, consisting of forms commonly found in other aquatic systems, but unlike other studies, we found filamentous VLP (FVLP) 450 to 730 nm long that attained abundances of up to 1.3 X 106 ml-1 and accounted for 7 to 100% of the total viral abundance. These FVLP were found occasionally inside filamentous heterotrophic bacteria (> 10 mum) and their respective abundances were positively correlated (rs = 0.728, p < 0.01). The absence of these conspicuous forms in other aquatic ecosystems suggests that FVLP are well adapted to the harsh environmental conditions or are specific to bacterial hosts found in alpine lakes. Finally, between 5 and 28% of the newly produced bacteria were killed by non-filamentous viruses, which therefore are a modest cause of bacterial mortality in this lake. [TOP OF PAGE]

  59. The chaperonins of Synechocystis PCC 6803 differ in heat inducibility and chaperone activity. Kovacs,E., van der Vies,S.M., Glatz,A., Torok,Z., Varvasovszki,V., Horvath,I., Vigh,L. (2001). Biochem Biophys Res Commun 289:908-915. The chaperonins GroEL and Cpn60 were isolated from the cyanobacterium Synechocystis PCC 6803 and characterized. In cells grown under optimal conditions their ratio was about one to one. However, the amount of GroEL increased considerably more than that of Cpn60 in response to heat stress. The labile chaperonin oligomer required stabilization by MgATP or glycerol during isolation. Use of the E. coli mutant strain, groEL44 revealed that the functional properties of the two cyanobacterial chaperonins are strikingly different. Overexpression of cyanobacterial GroEL in the E. coli mutant strain allowed growth at elevated temperature, the formation of mature bacteriophage T4, and active Rubisco enzyme assembly. In contrast, Cpn60 partially complemented the temperature-sensitive phenotype, the Rubisco assembly defect and did not promote the growth of the bacteriophage T4. The difference in chaperone activity of the two cyanobacterial chaperonins very probably reflects the unique chaperonin properties required during the life of Synechocystis PCC 6803. [TOP OF PAGE]

  60. Population dynamics and diversity of phytoplankton, bacteria and viruses in a seawater enclosure. Larsen,A., Castberg,T., Sandaa,R.A., Brussaard,C.P.D., Egge,J.K., Heldal,M., Paulino,A., Thyrhaug,R., van Hannen,E.J., Bratbak,G. (2001). Mar. Ecol. Prog. Ser. 221:47-57. We now know that the abundance of free viruses in most marine environments is high. There is still, however, a lack of understanding of their occurrence and distribution and of in situ relationships between viral and host communities in natural environments. This may be partly due to methodological limitations. Our main aim was therefore to perform a case study in which a variety of methods were applied in order to give an improved, high-resolution description of the microbial communities in a natural environment, In order to do this we combined light microscopy (LM), transmission electron microscopy (TEM), flow cytometry (FCM), PCR denaturing gradient gel electrophoresis (PCR-DGGE) and pulsed-field gel electrophoresis (PFGE) and studied the diversity and succession of algae, bacteria and viruses in a nutrient enriched seawater enclosure. In the enclosure we experienced a situation where the development of the dominating algal population, which consisted of several flagellate species, was followed by proliferation of several different size-classes of viruses. The total bacterial number decreased markedly during the flagellate bloom but the community composition was maintained and the diversity remained high. Our results indicate a close linkage between various algal, bacterial and viral populations and show that virioplankton do not necessarily terminate algal and bacterial blooms but that they keep the host populations at non-blooming levels. [TOP OF PAGE]

  61. A novel virus (HaNIV) causes lysis of the toxic bloom-forming alga Heterosigma akashiwo (Raphidophyceae). Lawrence,J.E., Chan,A.M., Suttle,C.A. (2001). J. Phycol. 37:216-222. We describe a previously unknown virus that causes lysis of the toxic blopm-forming alga Heterosigma akashiwo (Hada) Hara et Chihara (Raphidophyceae). Heterosigma akashiwo nuclear inclusion virus (HaNIV) does not resemble other algal viruses described to date. HaNIV is small (ca. 30 nm diameter), is assembled in the nucleus, and forms crystalline arrays. We estimate that approximately 105 HaNIV particles are released during lysis of a cell. During a time-course experiment, TEM revealed the first signs of HaNIV infection 24 h after viral addition, and by 74 h 98% of observed cells were visibly infected. The onset of cell lysis, as indicated by a decrease in the relative fluorescence of the cultures, was apparent by 42 h postinfection. The heterochromatin of infected cells is frequently found at the margin of the nucleoplasm, which is consistent with virus-mediated programmed cell death, or apoptosis. HaNIV is clearly different from other described viruses that infect alg ae, including other viral pathogens of H, akashiwo. These results indicate that viruses other than Phycodnaviridae are pathogens and cause mortality of microalgae in marine systems. It is Likely that HaNIV plays an integral role in the population dynamics of H. akashiwo. [TOP OF PAGE]

  62. Viruses in the plankton of freshwater and saline Antarctic lakes. Laybourn-Parry,J., Hofer,J.S., Sommaruga,R. (2001). Freshwater Biology 46:1279-1287. 1. Virus-like particle (VLP) abundances in nine freshwater to saline lakes in the Vestfold Hills, Eastern Antarctica (68degree S) were determined in December 1999. In the ultra-oligotrophic to oligotrophic freshwater lakes, VLP abundances ranged from 1.01 to 3.28 X 106 mL-1 in the top 6 m of the water column. In the saline lakes the range was between 6.76 and 36.5 X 106 mL-1. The lowest value was found in meromictic Ace Lake and the highest value in hypersaline Lake Williams. Virus to bacteria ratios (VBR) were lowest in the freshwater lakes and highest in the saline lakes, with a maximum of 23.4 in the former and 50.3 in the latter. 2. A range of morphologies among VLP was observed, including phages with short (Podoviridae) and long tails, icosahedric viruses of up to 300 nm and star-like particles of about 80 nm diameter. 3. In these microbially dominated ecosystems there was no correlation between VLP and either bacterial numbers of chlorophyll a. There was a significant correlation between VLP abundances and dissolved organic carbon concentration (r = 0.845, P < 0.01). 4. The data suggested that viruses probably attack a spectrum of bacteria and protozoan species. Virus-like particle numbers in the freshwater lakes were lower than values reported for lower latitude systems. Those in the saline lakes were comparable with abundances reported from other Antarctic lakes, and were higher than most values published for lower latitude lakes and many marine systems. Across the salinity spectrum from freshwater through brackish to hypersaline, VLP concentrations increased roughly in relation to increasing trophy. 5. Given that Antarctic lakes have a plankton almost entirely made up of bacteria and protists, and that VLP abundances are high, it is likely that viruses play a pivotal role in carbon cycling in these extreme ecosystems. [TOP OF PAGE]

  63. 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]

  64. Turning the phage on produce pathogens. McBride,J. (2001). Agricultural Research 2001(July), 12. Even bacteria have their nemesis. Tiny viruses, called phages, infect and kill bacteria naturally, including the foodborne pathogens that sometimes make humans so sick, they wish they were dead. ¶ So why not put these phages to work on fresh-cut fruit, thought ARS plant pathologists Britta Leverentz and William S. Conway at the Produce Quality and Safety Laboratory in Beltsville, Maryland. ¶ Since phages home in on a bacterium's surface proteins, they are very selective about their hosts. Phages specific for Salmonella, for instance, would leave beneficial bacteria free to multiply on fresh-cut produce and crowd out potential pathogens, Leverentz explains. ¶ What's more, these tiny viruses are natural, safe, and ubiquitous. A small dropperful of fresh water from a stream or lake, for example, contains an average 250 million phages. Before antibiotics, phages were used to treat human infections in the United States and are still used therapeutically in other parts of the world. ¶ Phages are already under study to control pathogens in poultry, meat, and eggs. Leverentz and Conway are the first to investigate their potential to reduce pathogens on fruits and vegetables— both whole and fresh-cut. They are working under a cooperative research and development agreement with Intralytix in Baltimore, Maryland, which is providing known phages for Salmonella Enteritidis. A patent application has been filed on the use of phages with produce. [TOP OF PAGE]

  65. Effects of bacteriophages on the population dynamics of four strains of pelagic marine bacteria. Middelboe,M., Hagstrom,A., Blackburn,N., Sinn,B., Fischer,U., Borch,N.H., Pinhassi,J., Simu,K., Lorenz,M.G. (2001). Microb. Ecol. 42:395-406. Viral lysis of specific bacterial populations has been suggested to be an important factor for structuring marine bacterioplankton communities. In the present study, the influence of bacteriophages on the diversity and population dynamics of four marine bacterial phage-host systems was studied experimentally in continuous cultures and theoretically by a mathematical model. By use of whole genome DNA hybridization toward community DNA, we analyzed the dynamics of individual bacterial host populations in response to the addition of their specific phage in continuous cultures of mixed bacterial assemblages. In these experiments, viral lysis had only temporary effects on the dynamics and diversity of the individual bacterial host species. Following the initial lysis of sensitive host cells, growth of phage-resistant clones of the added bacteria resulted in a distribution of bacterial strains in the phage-enriched culture that was similar to that in the control culture without phages after about 50-60 h incubation. Consequently, after a time frame of 5-10 generations after lysis, it was the interspecies competition rather than viral lysis of specific bacterial strains that was the driving force in the regulation of bacterial species composition in these experiments. The clonal diversity, on the other hand, was strongly influenced by viral activity, since the clonal composition of the four species in the phage-enriched culture changed completely from phage-sensitive to phage-resistant clones. The model simulation predicted that viral lysis had a strong impact on the population dynamics, the species composition, and the clonal composition of the bacterial community over longer time scales (weeks). However, according to the model, the overall density of bacteria in the system was not affected by phages, since resistant clones complemented the fluctuations caused by viral lysis. Based on the model analysis, we therefore suggest that viral lysis can have a strong influence on the dynamics of bacterial populations in planktonic marine systems. [TOP OF PAGE]

  66. Environmental bacteriophage-host interactions: Factors contribution to natural transduction. Miller,R.V. (2001). Antonie van Leeuwenhoek 79:141-147. Over the past two decades the potential for the exchange of bacterial genes in natural environments through transduction (bacteriophage-mediated gene transfer) has been well established. Studies carried out by various laboratories throughout the world have demonstrated that both chromosomal and plasmid DNA can be successfully transduced in natural environments ranging from sewer plants to rivers and lakes. Transduction has been shown to take place in the gills of oysters and the kidneys of mice. Model studies have demonstrated the ability of transduction to maintain genetic material in bacterial gene pools that would otherwise be lost because of negative fitness. Thus, transduction may affect the course of bacterial evolution. Identification of natural transduction has led to the investigation of the dynamics of bacteriophage host interactions in natural aquatic environments and to the exploration of various environmental factors that affect virus-host interactions. Two important environmental factors which affect virus-host interactions are the metabolic state of the host and the exposure of the host to DNA-damaging stresses such as solar UV light. Recent researches on these two areas of virus-host relationships are reviewed. [TOP OF PAGE]

  67. Validity of Escherichia coli, enterovirus, and F-specific RNA bacteriophages as indicators of viral shellfish contamination. Miossec,L., Le Guyader,F., Pelletier,D., Haugarreau,L., Caprais,M.P., Pommepuy,M. (2001). J. Shelfish Res. 20:1223-1227. The sanitary classification of harvesting areas for bivalve mollusks in France is based on the level of Escherichia coli contamination detected in shellfish meat, as defined in EC Directive 91/492 EEC. However, outbreaks of gastroenteritis or hepatitis after consumption of shellfish meeting current bacteriological standards suggest that E. coli is a poor indicator of viral contamination. The purpose of this study was to assess the adequacy of enterovirus and F-specific RNA bacteriophages as new indicators of human enteric viruses. Shellfish were sampled over a 37-mo period to characterize microbial contamination in two coastal areas subjected to different sewage contamination inputs. Contamination by E. coli, F-specific RNA bacteriophages (F+ RNA) and human enteric viruses (enterovirus, EV; hepatitis A virus, HAV; Norwalk-like virus, NLV; astrovirus, AV; and rotavirus, RV) was measured in the same samples. E. coli analysis was performed by conductance measurement, enteric viruses were detected by reverse-transcription polymerase chain reaction (RT-PCR) and hybridization, and F+ RNA was evaluated by culture according to the ISO 10705-1 method. Statistical analysis based on bootstrap methods was performed on 95 series of paired observations. The validity of E. coli, enterovirus, and F-specific RNA bacteriophages as viral indicators was evaluated by measuring their sensitivity and specificity in the presence of enteric viruses. None of the tested indicators proved adequate to protect the public from viral shellfish contamination. The sensitivity of all indicators was better in the highly contaminated zone, and enteroviruses showed the highest specificity for both sites. [TOP OF PAGE]

  68. Estimating viral proliferation in aquatic samples. Noble,R., Steward,G. (2001). Methods in Mcirobiology 30:67-84. It is only within the last decade that marine viruses were determined to be consistently the most abundant biological entities in the sea (Fuhrman, 1999). Since then, many advances have been made in understanding viral ecology (Fuhrman, 1999, Wilhelm and Suttle, 1999). Initial discoveries showed that viruses are both abundant in the ocean and that many bacteria are infected with viruses (Bergh et al., 1989; Proctor and Fuhrman, 1990). These data led researchers to believe that viruses are an important source of mortality in marine microbial food webs, but only provided a static picture. Subsequent studies have shown that virus populations are extremely dynamic, and can change quickly over short time scales (Bratbak et al 1990, 1996). Estimates of viral production and decay rates provided the valuable confirmation that viruses are active members of the marine community (Heldal and Bratbak, 1991; Steward et al., 1992b). The production of viruses implies the lysis of host cells and the release of cellular material as dissolved and colloidal organic carbon. Therefore, measurements of viral replication rates are also useful for assessing the contribution of viruses to bacterial mortality and organic matter cycling in the ocean. By assuming a burst size, viral productivity can be used to estimate rates of bacterial lysis. This approach provides an additional means to assess bacterial mortality along with the original electron microscopy-based method of Proctor and Fuhrman (1990). Accurate measurements of viral productivity and turnover are required if we are to properly model their dynamics and impact within the microbial food web. So far, however, there is no standard method for measuring viral productivity. A wide variety of different approaches have been used each with associated advantages and disadvantages. These methods include:
    1. Quantifying net increases in viral abundance over time (Bratbak et al., 1990)
    2. Measuring rates of viral decay (Heldal and Bratbak, 1991)
    3. Estimating viral DNA synthesis rates by radiolabeling (Steward et al., 1992a,b)
    4. Calculating expected viral release rates from estimated rates of bacterial lysis and an assumed burst size (Weinbauer et al., 1993)
    5. Measuring tracer dilution rates using fluorescently labeled viruses (FLV) as tracers (Noble and Fuhrman, submitted)
    The first approach, observing net increases in viruses over time, is the simplest means of demonstrating viral proliferation. However, use of this method is restricted to times when viral abundance is increasing and only provides a minimum estimate of productivity unless the viral decay rate is also known. The productivity estimates obtained are also dramatically influenced by the time scale of sampling (Bratbak et al., 1994, 1996). In the second approach, virus production is prevented by poisoning or removing host organisms and the rate at which viruses disappear (or decay) is observed. If the system was initially in steady state, the decay rate is assumed equal to the original rate of production. These two approaches have been used in a number of studies and variations on them are possible. Due to space limitations, however, this chapter focuses only on the last three methods listed above. [TOP OF PAGE]

  69. 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]

  70. Filamentous phage biology. Occurrence of coliphages in fish and aquaculture farms. Webster,R., Barbas,C.F., III, Burton,D.R., Scott,J.K., Silverman,G.J., Rao,B.M., Surendran,P.K. (2001). Fishery Technology 37:146-149. Coliphages were detected in water samples collected from brackish water and fresh water fish farms. Coliphages were also detected in the farmed fresh water fish, common carp and marine fish, oil sardine, from local market. Coliphage levels obtained were as follows:- water from brackish water fish farm 3 pfu.ml-1, water from fresh water fish farm 23 pfu.ml-1, fresh water fish 240 pfu.g-1 and marine fish 3500 pfu.g-1. [TOP OF PAGE]

  71. Interaction of the FHSIC virus with its host: lysogeny or pseudolysogeny? Williamson,S.J., McLaughlin,M.R., Paul,J.H. (2001). Appl. Environ. Microbiol. 67:1682-1688. The marine phage PhiHSIC has been previously reported to enter into a lysogenic relationship with its host, HSIC, identified as Listonella pelagia. This phage produces a variety of plaques on its host, including turbid and haloed plaques, from which lysogens were previously isolated. These lysogens were unstable during long-term storage at -80° C and were lost. When HSIC was reinfected with phage PhiHSIC, pseudolysogen-like interactions between the phage and its host were observed. The cells (termed HSIC-2 or HSIC-2e) produced high viral titers (1011 ml-1) in the absence of inoculating phage and yet reached culture densities of nearly 109 ml-1. Prophages were not induced by mitomycin C or the polyaromatic hydrocarbon naphthalene in cells harboring such infections. However, such cells were homoimmune to superinfection. Colonies hybridized strongly with a gene probe from a 100-bp fragment of the PhiHSIC genome, while the host did not. Analysis of chromosomal DNA preparations suggested the presence of a chromosomally integrated prophage. Phage adsorption experiments suggested that HSIC-2 was adsorption impaired. Because of the chromosomal prophage integration and homoimmunity, we interpret these results to indicate that PhiHSIC establishes a lysogenic relationship with its host that involves an extremely high level of spontaneous induction. This could be caused by a weak repressor of phage production. Additionally, poor phage adsorption of HSIC-2 compared to the wild type probably helped maintain this pseudolysogen-like relationship. In many ways, pseudolysogenic phage-host interactions may provide a paradigm for phage-host interactions in the marine environment. [TOP OF PAGE]

  72. Bacteriophage lambda and plasmid pUR288 transgenic fish models for detecting in vivo mutations. Winn,R.N., Norris,M., Muller,S., Torres,C., Brayer,K. (2001). Marine Biotechnology 3:185-195. We adapted transgenic rodent mutation assays based on fish carrying bacteriophage lambda and plasmid pUR288 vectors to address the needs for improved methods to assess health risks from exposure to environmental mutagens and also to establish new animal models to study in vivo mutagenesis. The approach entails separating the vectors from fish genomic DNA and then shuttling them into specialized strains of E. coli bacteria to analyze spontaneous and induced mutations in either lacI and cII or lacZ mutational targets. Fish exhibited low frequencies of spontaneous mutants comparable to the sensitivity of transgenic rodent models. Mutations detected after treating fish with chemical mutagens showed concentration-dependent, tissue-specific, and time-dependent relationships. Spontaneous and induced mutational spectra also were consistent with the specificity of known mutagens, further supporting the utility of transgenic fish for studies of in vivo mutagenesis. [TOP OF PAGE]

  73. Dynamic bacterial and viral response to an algal bloom at subzero temperatures. Yager,P.L., Connelly,T.L., Mortazavi,B., Wommack,K.E., Bano,N., Bauer,J.E., Opsahl,S., Hollibaugh,J.T. (2001). Limnol. Oceanogr. 46:790-801. New evidence suggests that cold-loving (psychrophilic) bacteria may be a dynamic component of the episodic bloom events of high-latitude ecosystems. Here we report the results of an unusually early springtime study of pelagic microbial activity in the coastal Alaskan Arctic. Heterotrophic bacterioplankton clearly responded to an algal bloom by doubling cell size, increasing the fraction of actively respiring cells (up to an unprecedented 84% metabolically active using redox dye CTC), shifting substrate-uptake capabilities from kinetic parameters better adapted to lower substrate concentrations to those more suited for higher concentrations, and more than doubling cell abundance. Community composition (determined by polymerase chain reaction/DGGE and nucleotide sequence analysis) also shifted over the bloom. Results support, for the first time with modern molecular methods, previous culture-based observations of bacterial community succession during Arctic algal blooms and confirm that previously observed variability in pelagic microbial activity can be linked to changes in community structure. During early bloom stages, virioplankton and bacterial abundance were comparable, suggesting that mortality due to phage infection was low at that time. The virus-to-bacteria ratio (VBR) increased 10-fold at the height of the bloom, however, suggesting an increased potential for bacterioplankton mortality resulting from viral infection. The peak in VBR coincided with observed shifts in both microbial activity and community structure. These early-season data suggest that substrate and virioplankton interactions may control the active microbial carbon cycling of this region. [TOP OF PAGE]

  74. Symposium on Harmful Marine Algae in the U.S. Anonymous (2000). [TOP OF PAGE]

  75. Role of ciliates, flagellates and bacteriophages on the mortality of marine bacteria and on dissolved-DNA concentration in laboratory experimental systems. Alonso,M.C., Rodriguez,V., Rodriguez,J., Borrego,J.J. (2000). Journal of Experimental Marine Biology and Ecology 244:239-252. Several marine bacteriophages, a ciliate (Uronema sp.), and a flagellate (Pseudobodo sp.) were used to study comparatively the grazing and clearance rates of four marine bacteria. Bacteria were fluorescently labelled using rhodamine isothiocyanate. The results obtained indicate that bacteriophages and flagellates caused a significantly higher (P < 0.025) decrease in the number of marine bacteria compared to the ciliate Uronema sp. The role of bacteriophages, ciliates and flagellates in the production of dissolved-DNA (D-DNA) was also studied. The interaction between both bacteriophages and protists with marine bacteria are responsible for an increase of the D-DNA concentration, although a direct relationship between D-DNA concentration and predator number was only obtained from experiments performed with Uronema sp. [TOP OF PAGE]

  76. Microbiological quality of the Catania coastal sea water. Aulicino,F.A., Mauro,L., Marranzano,M., Biondi,M., Ursino,A., Carere,M. (2000). Annali di Igiene 12:533-541. This study was carried out from 1997 to 1998 along a selected coastal area near Catania to ascertain bacteriological and virological quality of marine waters. 44 seawater samples, collected from 4 stations, were assayed for the presence of total and fecal coliforms, fecal streptococci, coliphages, Salmonellae and enteric viruses. Two stations localized at canal outfalls showed high levels of fecal pollution. The other stations were of good microbiological quality and showed a limited number of samples exceeding the standards laid down as guide values for bathing waters by Italian normative during the bathing period. Salmonellae were isolated in 8 out of 44 sea water samples (18%). Their presence was ascertained mainly in samples of the two polluted stations. Enteroviruses were not isolated. Enteric viruses such as Reoviruses were isolated from all stations, in 12 out of 44 samples (27%). The presence of these viruses was ascertained only during autumnal and winter seasons. The results of this study showed that, notwithstanding some stations showed high levels of bacteriological indicators of fecal pollution and presence of Salmonellae, enteroviruses growing on cell cultures were not isolated. Reoviruses confirmed their high diffusion in marine waters. [TOP OF PAGE]

  77. The presence of viruses and bacteria along the Adriatic Coast. Aulicino,F.A., Ammazzalorso,P., Ercolessi,M., Banini,L., Silverii,G., Orsini,P., Mastrantonio,A., Bellucci,C., Carere,M. (2000). Ig. Mod. 113:99-116. A study was carried out on seawater samples, collected from the Adriatic sea near the coast of Pesaro, to determine the presence of enteric viruses and Escherichia coli bacteriophages besides the common indicators of fecal pollution and of trophic conditions of the marine environment (Pseudomonas, Vibrio, algae). During 1994-95, seawater samples were tested in 8 stations located in seaside resorts; in 1994 samples of sediment were also analyzed. Generally the results showed a good situation from the microbiological and eutrophic point of view. Only 2 stations showed fecal pollution. Enteroviruses were not detected while Reovirus was isolated from samples of the two most contaminated stations and from a not polluted area. [TOP OF PAGE]

  78. Light scattering by viral suspensions. Balch,W.M., Vaughn,J., Novotny,J., Drapeau,D.T., Vaillancourt,R., Lapierre,J., Ashe,A. (2000). Limnol. Oceanogr. 45:492-498. Viruses represent one of the most abundant, ocean-borne particle types and have significant potential for affecting optical backscattering. Experiments addressing the light-scattering properties of viruses have heretofore not been conducted. Here we report the results of laboratory experiments in which the volume-scattering functions of several bacterial viruses (bacteriophages) were measured at varying concentrations with a laser light-scattering photometer using a He-Ne and/or Argon ion laser (632.8 and 514.0 nm, respectively). Four bacterial viruses of varying size were examined, including the coliphages MS-2 (capsid size 25-30 nm) and T-4 (capsid size apprx100 nm), and marine phages isolated from Saco Bay, Maine (designation Y-1, capsid size 50-80 nm) and Boothbay Harbor, Maine (designation C-2, capsid size apprx110 nm). Volume-scattering functions (VSFs) were fitted with the Beardsley-Zaneveld function and then integrated in the backward direction to calculate backscattering cross section. This was compared to the virus geometric cross section as determined by transmission electron microscopy and flow-field fractionation. Typical backscattering efficiencies varied from 20 X 10-6 to 1,000 X 10-6. Data on particle size and backscattering efficiencies were incorporated into Mie scattering calculations to estimate refractive index of viruses. The median relative refractive index of the four viruses was apprx1.06. Results presented here suggest that viruses, while highly abundant in the sea, are not a major source of backscattering. [TOP OF PAGE]

  79. Evolution of life's fringes. Balter,M. (2000). Science 289:1866-1867. Fresh evidence that viruses have existed for billions of years has scientists wondering what role these stripped-down microbes played in evolution. [TOP OF PAGE]

  80. Viral density and virus-to-bacterium ratio in deep-sea sediments of the Eastern Mediterranean. Danovaro,R., Serresi,M. (2000). Appl. Environ. Microbiol. 66:1857-1861. Viruses are now recognized as a key component in pelagic systems, but their role in marine sediment has yet to be assessed. In this study bacterial and viral densities were determined at nine deep-sea stations selected from three main sites (i.e., the Sporades Basin, the Cretan Sea, and the Ierapetra Trench at depths of 1,232, 1,840, and 4,235 m, respectively) of the Eastern Mediterranean. The three areas were characterized by different phytopigment and biopolymeric carbon concentrations and by changes in the protein and carbohydrate pools. A gradient of increasing trophic conditions was observed from the Sporades Basin (North Aegean) to the Ierapetra Trench (South Aegean). Viral densities (ranging from 1 x 109 to 2 x 109 viruses ml of sediment(-1)) were significantly correlated to bacterial densities (n = 9, r2 = 0.647) and reached values up to 3 orders of magnitude higher than those generally reported for the water column. However, the virus-to-bacterium density ratio in deep-sea sediments was about 1 order of magnitude lower (range of 2 to 5, with a modal value of 2.6) than in pelagic environments. Virus density decreased vertically with depth in sediment cores at all stations and was below detection limits at the 10-cm depth of the abyssal sediments of the Ierapetra Trench. Virus density in the sediment apparently reflected a gradient of particle fluxes and trophic conditions, displaying the highest values in the Sporades Basin. The low virus-to-bacterium ratios and their inverse relationship with station depth suggest that the role played by viruses in controlling deep-sea benthic bacterial assemblages and biogeochemical cycles is less relevant than in pelagic systems. [TOP OF PAGE]

  81. Pulsed-field gel electrophoresis analysis of virus assemblages present in a hypersaline environment. Diez,B., Anton,J., Guixa-Boixereu,N., Pedros-Alio,C., Rodriguez-Valera,F. (2000). International Microbiology 3:159-164. A method for analyzing virus assemblages in aquatic environments was developed and used for studying the highest-salinity ponds (from 13.4 to 35% salinity) from a multi-pond solar saltern in Alicante, Spain. The protocol consisted of a series of concentration and purification steps including tangential flow filtration and ultracentrifugation, followed by the preparation of total viral nucleic acids that were subsequently separated by pulsed-field gel electrophoresis. For every sample analyzed, a characteristic DNA pattern was obtained, whose complexity was related to viral diversity. The comparison of our results with a similar analysis carried out with marine virus assemblages shows that, as expected, the viral diversity corresponding to the analyzed hypersaline environment is considerably lower than that of a marine environment. [TOP OF PAGE]

  82. Causative agents of bacterial mortality and the consequences to marine food webs. Fuhrman,J.A., Noble,R.T. (2000). p. ??? In Bell,C.R., Brylinsky,M., and Johnson-Green,P. (eds.), Microbial Biosystems: New Frontiers. Atlantic Canada Society for Microbial Ecology, Halifax, Canada. [TOP OF PAGE]

  83. Ultraviolet radiation effects on bacterioplankton and viruses in marine ecosystems. Jeffrey,W.H., Kase,J.P., Wilhelm,S.W. (2000). pp. 206-236. In In De Mora,S.J. and et al. (eds.), Effects Of UV Radiation On Marine Ecosystems. Cambridge University Press, Cambridge. [TOP OF PAGE]

  84. 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]

  85. Bacterial growth rate and marine virus–host dynamics. Middelboe,M. (2000). Microb. Ecol. 40:114-124. The dynamics of a marine virus–host system were investigated at different steady state growth rates in chemostat cultures and the data were analyzed using a simple model. The virus–host interactions showed strong dependence on host cell growth rate. The duration of the infection cycle and the virus burst size were found to depend on bacterial growth rate, and the rate of cell lysis and virus production were positively correlated with steady state growth rate in the cultures (r 2 > 0.96, p < 0.05). At bacterial growth rates of 0.02 to 0.10 h-1 in the chemostats the virus burst size increased from 12 ± 4 to 56 ± 4, and the latent period decreased from 2.0 to 1.7 h. Resistant clones of the host strain were present in the cultures from the beginning of the experiment and replaced the sensitive host cells following viral lysis in the cultures. Regrowth of resistant cells correlated significantly (r 2 = 1.000, p < 0.02) with the lysis rate of sensitive cells, indicating that release of viral lysates stimulated growth of the non-infected, resistant cells. The constructed model was suitable for simulating the observed dynamics of the sensitive host cells, viruses and resistant clones in the cultures. The model was therefore used in an attempt to predict the dynamics of this virus–host interaction in a natural marine environment during a certain set of growth conditions. The simulation indicated that a steady state relationship between the specific viruses and sensitive and resistant bacterial clones may occur at densities that are reasonable to assume for natural environments. The study demonstrates that basic characterization and modeling of specific virus–host interactions may improve our understanding of the behavior of bacteria and viruses in natural systems. [TOP OF PAGE]

  86. Rapid movement of wastewater from on-site disposal systems into surface waters in the Lower Florida Keys. Paul,J.H., McLaughlin,M.R., Griffin,D.W., Lipp,E.K., Stokes,R., Rose,J.B. (2000). Estuaries 23:662-668. Viral tracer studies have been used previously to study the potential for wastewater contamination of surface marine waters in the Upper and Middle Florida Keys. Two bacteriophages, the marine bacteriophage phiHSIC and the Salmonella phage PRD1, were used as tracers in injection well and septic tank studies in Saddlebunch Keys of the Lower Florida Keys and in septic tank studies in Boot Key Harbor, Marathon, of the Middle Keys. In Boot Key Harbor, both phages were detected in a canal adjacent to the seeded septic tank within 3 h 15 min of the end of the seed period. The tracer was then detected at all sampling sites in Boot Key Harbor, including one on the opposite side of U.S. Highway 1 in Florida Bay, and at an Atlantic Ocean beach outside Boot Key Harbor. Rates of migration based on first appearance of the phage ranged from 1.7 to 57.5 m h-1. In Saddlebunch Keys, phiHSIC and PRD1 were used to seed a residential septic tank and a commercial injection well. The septic tank tracer was not found in any surface water samples. The injection well tracer was first detected at a site most distant from the seed site, a channel that connected Sugarloaf Sound with the Atlantic Ocean. The rate of tracer migration from the injection well to this channel ranged from 66.8 to 141 m h-1. Both tracer studies showed a rapid movement of wastewater from on-site sewage treatment and disposal systems in a southeasterly direction toward the reef tract and Atlantic Ocean, with preferential movement through tidal channels. These studies indicate that wastewater disposal systems currently in widespread use in the Florida Keys can rapidly contaminate the marine environment. [TOP OF PAGE]

  87. Evaluation of marine bacterial lysogens for use in a mutagen detection (Prophage Induction) assay. Paul,J.H., Griffin,D.W., Crespo-Gomez,J., McDaniel,L., McLaughlin,M.R. (2000). Abstracts of the General Meeting of the American Society for Microbiology 100, 464. [TOP OF PAGE]

  88. 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]

  89. Occurrence of coliphages in fish and aquaculture farms. Rao,B.M., Surendran,P.K. (2000). Fishery Technology 37:146-149. Coliphages were detected in water samples collected from brackish water and fresh water fish farms. Coliphages were also detected in the farmed fresh water fish, common carp and marine fish, oil sardine, from local market. Coliphage levels obtained were as follows:- water from brackish water fish farm 3 pfu.ml-1, water from fresh water fish farm 23 pfu.ml-1, fresh water fish 240 pfu.g-1 and marine fish 3500 pfu.g-1. [TOP OF PAGE]

  90. The complete genomic sequence of the marine phage Roseophage SIO1 shares homology with nonmarine phages. Rohwer,F., Segall,A., Steward,G., Seguritan,V., Breitbart,M., Wolven,F., Azam,F. (2000). Limnol. Oceanogr. 45:408-418. Viruses are ubiquitous components of the marine environment, frequently reaching concentrations of 107-108 viruses per milliliter of surface seawater The majority of these viral particles are bacteriophages (phages). Although the oceans are probably the largest pool of bacteriophages on the planet, the evolutionary relationships of marine phages to phages from other environments are unknown. To address this issue, we have completely sequenced the genome of the lytic marine phage, Roseophage SIO1, that infects the heterotrophic marine bacterium Roseobacter SIO67. This phage has an isometric capsid with a diameter of approximately 43 nm, a short tail, a buoyant density of 1.49 g cm-3 in CsCl, and a 39,906-bp dsDNA genome. Sequence similarities and relative positions within the genome suggest that three of the open reading frames (ORFs) are homologous to the primase, DNA polymerase, and endodeoxyribonuclease I proteins of coliphages T3 and T7. The results are consistent with the mosaic theory of phage evolution and indicate a genetic link between marine and nonmarine phages. Additionally, basic life histories of marine phages can be elucidated by comparison of complete genomes to those of other extensively studied phages (e.g., lambda, T4, T7