Supplemental Lecture (98/04/06 update) by Stephen T. Abedon (abedon.1@osu.edu)

  1. Chapter title: Non Nutrient Factors Affecting Growth
    1. A list of vocabulary words is found toward the end of this document
  2. Physical parameters affecting growth
    1. Physical parameters affecting growth include such things as:
      1. temperature
      2. pH
      3. oxygen requirements
      4. osmotic pressure
      5. presence or absence of moisture
      6. presence or absence of light
      7. presence of radiation
      8. hydrostatic pressure
  3. Optimal growth temperature
    1. Microorganisms tend to have temperature ranges at which their growth is optimized.
    2. Range categories:
      1. Microorganisms may be categorized according to these temperatures. Particularly, what category they fall into is defined by their:
      2. minimum growth temperatures
      3. maximum growth temperatures
      4. optimal growth temperatures
    3. For most bacteria, the range from minimum to maximum is about 30°C (e.g., from 44°C down to 14°C).
    4. "Regardless of the type of bacteria, growth gradually increases from the minimum to the optimum temperature and decreases very sharply from the optimum to the maximum temperature. Furthermore, the optimum temperature is often very near the maxiumum temperature." (p. 146, Black, 1986)
    5. Temperature extremes:
      1. For many bacteria both extremely high and extremely low temperatures can be quite harmful, the former due to protein denaturation, the latter due to intracellular ice crystal formation upon freezing.
      2. There neverthless exist microorganisms whose optimum growth temperatures might be considered extreme.
    6. Optimal growth temperature categories:
      1. Microorganisms with various temperature characteristics are referred to as:
      2. psychrophiles
      3. psychotrophs
      4. mesophiles
      5. thermophiles
  4. Psychrophiles
    1. Low growth optimum:
      1. Psychrophiles are microoganisms whose optimum growth temperature is colder than that seen with most microorganisms.
      2. Typically these organisms have an temperature optimum ranging from 15°C to 20°C.
    2. Psychrophiles are capable, for example, of growth at, near, or even below the freezing point of water.
  5. Thermophiles
    1. Microoganisms whose optimum growth temperature is warmer than that seen with most microorganisms are called thermophiles.
    2. Such organisms can grow and prosper at temperatures in excess of what would denature key proteins in most organisms (i.e., typically 50°C), up to and including the temperature of water boiling at sea level.
  6. Mesophiles
    1. Medium growth optimum:
      1. In between these two extremes are those microorganisms found in most environments (including typically inside the bodies of warm-blooded animals).
      2. These intermediate-temperature loving microorganisms are called mesophiles.
    2. Mesophiles are bacteria which have an optimal temperature of between 25°C and 40°C.
    3. Most common type of bacteria.
    4. Includes those which live on warm-blooded animals:
      1. Mesophiles are the category of bacteria that live in the bodies of warm-blooded animals.
      2. Most pathogens of warm-blooded organisms are mesophiles.
      3. Vibrio cholera is an exception.
  7. Thermoduric
    1. Some mesophiles are capable of short exposures to relatively high temperatures. These are described as thermoduric.
  8. Refrigeration
    1. The limitations of mesophile growth and survival explains why refrigeration as well as Pasteurization work to minimize the growth particularly of mesophilic pathogens.
    2. Preserving perishables:
      1. Storing perishable items at lower temperatures:
        1. completely eliminates the ability of mesophiles to grow
        2. slows down the rate of all chemical reactions thus slowing the growth of any microorganisms (i.e., psychrotrophs) capable of growing at low temperatures and likely to be in your refrigerator
        3. slows down the autodigestion of produce (i.e., of themselves, by themselves)
    3. Refrigeration prevents the growth of most pathogenic microorganisms (that is, it has a bacteriostatic effect).
  9. Psychrotroph
    1. Psychrotrophs are microorganisms that have a minimum growth temperature below that commonly found in refrigerators but an optimal growth temperature around room temperature.
    2. Nuisance:
      1. Such organisms are environmentally common even at lower latitudes because they grow at typical ambient temperatures.
      2. However, they are a nuisance because they grow on refrigerated food.
      3. That is, psychotrophs are organisms which grow only at low temperatures (i.e., psychrophiles) might be capable of growth on refrigerated food, but typically are not found in high numbers in the environment immediately surrounding the refrigerator.
  10. Optimal pH [acidophiles, neutrophiles, alkaliphiles]
    1. pH range:
      1. The growth of the majority of bacteria is limited to a pH range of appoximately 2 (i.e., one above to one below their optimum pH).
      2. pH range classifications include:
        1. acidophile (pH < 5.4)
        2. neutrophile (pH 5.4 - 8.5)
        3. alkaliphile (pH 7.0 - 11.5)
    2. Neutrophile pathogens:
      1. Most human pathogens are neutrophiles, i.e., the have optimal pHs which bracket pH 7.
      2. An exception is Vibrio cholerae which is a alkaliphile.
  11. Optimal osmotic pressure [halophiles]
    1. Water unavailability = low growth:
      1. High extracellular osmotic pressures remove water from cells (i.e., desiccation; see plasmolysis). This inhibits cell growth.
      2. Consequently, high solute solutions tend to inhibit growth by most microorganisms capable of growing at the typically low solute concentrations of most environments.
    2. The exceptions are organisms adapted to growth at relatively high and very high salt concentrations, which are referred to as facultative and extreme halophiles, respectively.
    3. Fungi more resistant:
      1. Molds and yeasts tend to be much more resistant to high or low osmotic pressures than are bacteria.
      2. This is one reason that molds, but not bacteria, tend to be the spoilers of fruits and grains.
  12. Oxygen requirements
    1. There are many degrees of oxygen requirement among microorganisms. Organisms may thus be described as:
      1. aerobes
      2. obligate aerobes
      3. facultative anaerobes
      4. microaerophiles
      5. anaerobes
      6. aerotolerant anaerobes
      7. obligate (strict) anaerobe
  13. Aerobe
    1. An aerobe is a microorganism that can utilize molecular oxygen as its final electron acceptor, i.e., as in cellular (aerobic) respiration.
  14. Obligate aerobe
    1. No fermentation:
      1. An obligate aerobe is a microorganism that cannot live in the absence of molecular oxygen.
      2. This basically means that they cannot obtain energy via fermentative processes.
      3. More precisely, obligate aerobes are organisms that
        1. have an electron transport system
        2. are able to grow in the presence of atmospheric oxygen concentrations
        3. can use O2 as a final electron acceptor
        4. cannot ferment
    2. Examples:
      1. Bacillus subtilis
      2. Bdellovibrio spp.
      3. Bordetella pertussis
      4. Legionella spp.
      5. Mycobacterium leprae
      6. Mycobacterium tuberculosis
      7. Neisseria gonorrhoeae
      8. Neisseria meningitidis
      9. Pseudomonas spp.
    3. anaerobic respiration:
      1. Organisms capable of anaerobic respiration but not fermentation are included among the obligate aerobes (e.g., Pseudomonas spp.).
      2. Thus, the ability to grow in the absence of oxygen is possible for at least some non-fermentors.
  15. Facultative anaerobe
    1. A facultative anaerobe is an aerobic microorganism that can utilize fermentation when molecular oxygen is absent, and can utilize aerobic cellular respiration when O2 is present.
    2. Note that the term facultative is often used synonimously with facultatively anaerobic as in "facultative organism".
    3. Examples:
      1. Bacillus anthracis
      2. Corynebacterium diphtheriae
      3. Escherichia coli
      4. Gardnerella vaginalis
      5. Hemophilus influenzae
      6. Klebsiella spp.
      7. Lactobacillus spp. (can also be microaerophilic)
      8. Listeria monocytogenes
      9. Mycoplasma pneumoniae
      10. Pasteurella pestis
      11. Proteus spp.
      12. Salmonella spp.
      13. Serratia marcescens
      14. Shigella spp.
      15. Staphylococcus aureus
      16. Streptococcus spp.
      17. Vibrio cholerae
      18. Yersinia pestis
    4. For those organisms for which you are required to memorize their oxygen utilization status, note that approximately half can be found among the facultative anaerobes.
  16. Anaerobe
    1. O2 not final electron acceptor:
      1. An anaerobe is a microorganism that need not utilize molecular oxygen as a final electron acceptor (i.e., in order to produce ATP).
      2. Anaerobes can employ fermentation to generate ATP.
      3. Nonfacultative anaerobes can only employ fermentation to generate ATP.
      4. Some anaerobes are capable of growh in the presence of O2 and consequently cannot be described as strict anaerobes.
    2. Clostridium perfringens and Treponema pallidum are examples of organisms which are not facultative anaerobes but which are capable of growth in the presence of some O2 (some isolates of Treponema pallidum are instead microaerophiles).
  17. Obligate [strict] anaerobe
    1. O2 intolerant:
      1. Many anaerobes not only can't utilize molecular oxygen but are harmed by it as well.
      2. One usage of the term obligate anaerobe is to describe only those microorganisms which are unable to grow (and, for that matter, even survive) in the presence of molecular oxygen.
      3. The other, less strict usage of the term obligate anaerobe is simply to distinguish the term "anaerobe" from the term "facultative anaerobe."
      4. Of bacterium which are incapable of survival in the presence of O2 are included Clostridium botulinum and Clostridium tetani.
  18. Aerotolerant anaerobe
    1. An aerotolerant anaerobe is a non-facultative anaerobe that nevertheless is able to grow in the presence of molecular oxygen.
  19. Microaerophile
    1. Low O2 requirement and tolerance:
      1. Microaerophiles are microorganisms which are unable to grow when oxygen concentrations reach those found in air (20%) but nevertheless whose growth requires the presence of some oxygen (e.g., 2 to 10%).
      2. "Microaerophiles appear to grow best in the presence of a small amount of free oxygen. They grow below the surface of the medium in a culture tube at the level where oxygen availability matches their needs." (p. 147, Black, 1986)
    2. The enzyme nitrogenase is poisoned by normal atmospheric oxygen levels thus rendering nitrogen fixation nonoperative. Nitrogen fixing bacteria have a consequent growth preference for lower than normal atmospheric levels of oxygen.
    3. Examples:
      1. Borrelia burgdorferi
      2. Helicobacter pylori
      3. Lactobacillus spp. (can also be a facultative anaerobe)
      4. Treponema pallidum (can also be an anaerobe)
    4. The in many ways similar Treponema pallidum and Borrelia burgdorferi spirochetes are also both examples of microaerophilic bacteria. Note, however, that Bergey's classifies T. pallidum as "Anaerobic or microaerophilic." (p. 30, 1994, Nineth Edition)
    5. Microaerophilic conditions, though not necessarily just microaerophilic microorganisms, may be found in some environments particularly at the interface between the anaerobic and the aerobic such as those found in soil, water, or part of the bodies of animals and some plants.
    6. The colon is maintained anaerobic by the scavenging of oxygen by facultative anaerobes living near the intestinal wall (and thus the source of oxygen in this system). Areas close to the intestinal wall (especially, intimately in contact with it) are therefore maintained in a microaerophilic state.
  20. Vocabulary
    1. Aerobe
    2. Aerotolerant anaerobe
    3. Facultative anaerobe
    4. Mesophile
    5. Microaerophile
    6. Obligate aerobe
    7. Obligate anaerobe
    8. Psychrotroph
    9. Physical parameters affecting growth
  21. Practice questions
    1. Which are you more likely to find growing in your refrigerator (circle only one correct answer)? [PEEK]
      1. a psychrophile
      2. a mesophile
      3. an endospore
      4. a psychrotroph
      5. all of the above
      6. none of the above
    2. A microorganism that can live in air but doesn't have an electron transport chain is a(n) (circle only one correct answer)? [PEEK]
      1. aerobe
      2. obligate anaerobe
      3. facultative anaerobe
      4. aerotolerant anaerobe
      5. microaerophile
      6. obligate aerobe
      7. all of the above
      8. none of the above
    3. Flask A contains yeast cells in glucose-minimal salts broth incubated at 30°C with aeration. Flask B contains yeast cells in glucose-minimal salt broth incubated at 30°C in an anaerobic jar. The yeasts are facultative anaerobes. Circle either A or B at the end of each line (note: four correct = half credit; five correct = full credit) (p. 166, Tortora et al., 1995): [PEEK]
      1. Which culture produced more ATP (A or B)?
      2. Which culture produced more alcohol (A or B)?
      3. Which culture had the shorter generation time (A or B)?
      4. Which culture had the greater cell mass (A or B)?
      5. Which culture had the higher absorbance (A or B)?
    4. Recently, researchers found that when E. coli cells are exposed to a hyperosmotic solution, the bacteria produce a permease that can move K+ into the cell. Of what value is the active transport of K+, which requires ATP. ([PEEK]
    5. An anaerobic microorganism which can live in the air but only if oxygen concentrations are significantly reduced is a(n) . . . (choose best answer). [PEEK]
      1. aerobe
      2. obligate anaerobe
      3. facultative anaerobe
      4. aerotolerant anaerobe
      5. microaerophile
      6. obligate aerobe
      7. all of the above
      8. none of the above
    6. In terms of non-nutrient growth factors affecting growth, name one way molds and yeasts differ from bacteria? [PEEK]
    7. You have a bacteria which you find grows at 23°C but not at temperatures below 22°C. What would you guess would be the approximate maximum temperature at which it can grow? [PEEK]
      1. 25°C
      2. 37°C
      3. 45°C
      4. 52°C
      5. 65°C
      6. none of the above (give temperature: _____________)
      7. insufficient data
    8. Bacteria and fungi both often fill niches associated with the absorption of simple nutrients from the environment. Often these nutrients are predigested, and therefore made simple and absorbable by digestive enzymes secreted into the external environment (exoenzymes). How can it be that two groups of organisms which obtain their nutrients in such a similar manner can simultaneously persist? In part, this coexistence of bacteria and fungi may be explained in terms of differences in their nutrient preferences (animal vs. plant products, respectively, for example). Another key difference between bacteria and fungi, that assures the survival of both, are generally divergent adaptations to various physical aspects of their environment. Physically, how might you expect the optimal growth environments of a typical fungi to differ from that of a typical bacteria? Give a single example. [PEEK]
    9. The following are minimal and maximal growth temperatures associated with hypothetical bacteria. In terms of your understanding of optimal growth temperatures, which range would you consider the least believable? [PEEK]
      1. 69°C to 99°C
      2. 22°C to 52°C
      3. 4°C to 30°C
      4. 34°C to 39°C
      5. 14°C to 44°C
    10. Human beings (Homo sapiens) are (circle best answer)? [PEEK]
      1. aerobes
      2. obligate anaerobes
      3. facultative anaerobes
      4. aerotolerant anaerobes
      5. microaerophiles
      6. obligate aerobes
      7. all of the above
      8. none of the above
    11. You wonder whether potentially halophilic bacteria might be present in soil found about an ocean dune. Describe how you might isolate a halophile from a complex mixture of bacteria. [PEEK]
    12. Circle all of the facultatively anaerobic endospore formers (i.e., organisms that have both of these properties). [PEEK]
      1. Bacillus anthracis, Bacillus subtilis, Bdellovibrio spp., Bordetella pertussis, Borrelia burgdorferi, Chlamydia trachomatis, Clostridium botulinum, Clostridium perfringens, Clostridium tetani, Corynebacterium diphtheriae, Escherichia coli, Gardnerella vaginalis, Helicobacter pylori, Hemophilus influenzae, Klebsiella spp., Lactobacillus spp., Legionella spp., Listeria monocytogenes, Mycobacterium leprae, Mycobacterium tuberculosis, Mycoplasma pneumoniae, Neisseria gonorrhoeae, Neisseria meningitidis, Pasteurella pestis, Proteus spp., Pseudomonas spp., Rickettsia prowazekii, Rickettsia rickettsii, Salmonella spp., Serratia marcescens, Shigella spp., Staphylococcus aureus, Streptococcus spp., Treponema pallidum, Vibrio cholerae, Yersinia pestis
    13. True or false, all human pathogens have an optimal growth temperature of 37°C. [PEEK]
    14. True or false, fastidiousness has nothing to do with oxygen requirements. (circle one correct answer) [PEEK]
    15. Why does refrigeration prevent the growth of most microorganisms which are pathogenic to humans? [PEEK]
    16. Which of the following is not an obligate aerobe? [PEEK]
      1. Bacillus subtilis
      2. Pseudomonas spp.
      3. Mycobacterium spp.
      4. Corynebacterium diphtheriae
      5. Neisseria gonorrhoeae
      6. Bordetella pertussis
    17. Name two things that Borrelia burgdorferi and at least some strains of Treponema pallidum have in common. [PEEK]
    18. What is the oxygen requirement of Borrelia burgdorferi? [PEEK]
    19. What is a psychrotroph? [PEEK]
    20. A microorganism which can withstand and even grow at extremely high osmotic pressures is an example of a _____phile [PEEK]
  22. Practice question answers
    1. iv, psychrotroph (unless, of course, you live in the arctic)
    2. iv, aerotolerant anaerobe
    3. (i) A, (ii) B, (iii) A, (iv) A, (v) A
    4. increases intracellular solute concentration bringing it closer to that of the hyperosmotic extracellular environment and thus reducing the severity of plasmolysis.
    5. iv, aerotolerant anaerobe. The answer is not microaerophile since microaerophiles require at least some oxygen to grow and therefore cannot strictly be classified as anaerobic.
    6. Fungi are more resistant to higher osmotic pressures. Fungi are more resistant to lower pHs. Fungi also tend to display tolerance to a wider range of pHs than do bacteria.
    7. iv, 52°C. Answer is based on the rule of thumb that the range of temperature over which a bacteria may grow is about 30°C
    8. In general fungi are adapted to growth at higher osmotic pressures as well as lower pHs.
    9. iv, 34°C to 39°C. All of the other ranges span 30°C (or nearly so). The bacteria with a range of 34°C to 39°C spans only 6°C. While certainly plausible, this is an unexpectedly narrow range. Note that the range of 69°C to 99°C could be typical for an extreme thermophile such as that exhibited by many archaeobacteria.
    10. vi, obligate aerobes (and if you don't believe me, start holding your breath, now . . .
    11. Use a selective media which is high in salt.
    12. Bacillus anthracis.
    13. False, through many do, not all of them do, with Mycobacterium leprae being a notable exception though there are many others, particularly those which produce ingested toxins.
    14. True.
    15. Most pathogenic microorganisms are mesophiles and consequently fail to grow at refrigerated temperatures.
    16. Corynebacterium diphtheriae
    17. both are spirochetes, both are microaerophiles.
    18. Microaerophilic
    19. a microbe capable of growth at refrigeration temperatures, but with a temperature optimum well about refrigeration temperatures
    20. halo
  23. References
    1. Black, J.G. (1996). Microbiology. Principles and Applications. Third Edition. Prentice Hall. Upper Saddle River, New Jersey. pp. 144-148.
    2. Campbell, N.A. (1996). Biology. Fourth Edition. Benjamin/Cummings Pub. Co. Menlo Park, CA. p. 508.
    3. McKane, L., Kandel, J. (1996). Microbiology: Essentials and Applications. Second Edition. McGraw-Hill, Inc., New York. p. 110.
    4. Tortora, G.J., Funke, B.R., Case, C.L. (1995). Microbiology. An Introduction. Fifth Edition. The Benjamin/Cummings Publishing, Co., Inc., Redwood City, CA, pp. 142-145, 146-147.
    5. Prescott, L.M. , Harley, J.P., Klein, D.A. (1996). Microbiology. Third Edition. Wm. C. Brown Publishers. Dubuque, IA. p. 130.
    6. Talaro, K., Talaro, A. (1996). Foundations in Microbiology. Second Edition. Wm. C. Brown Publishers. Dubuque, IA. p. 205.