Microbial Nutrition and Growth Microbial Ecology

1. Microbial Nutrition and GrowthMicrobial Ecology Microbiology for Health Sciences

2. Factors that May Affect Growth Oxygen Temperature pH Osmotic Pressure

3. Oxygen Requirements • Aerobe: uses oxygen for metabolism • Facultative Anaerobe: does not require oxygen for metabolism • Microaerophile: requires small amounts of oxygen for metabolism • Strict Anaerobe: require element other than oxygen for metabolism, N, S, CO2

4. Several General Categories of Oxygen Requirements • Aerobe: can use gaseous oxygen in its metabolism and possesses the enzymes needed to process toxic oxygen products • Obligate aerobe: cannot grow without oxygen • Facultative anaerobe: an aerobe that does not require oxygen for its metabolism and is capable of growth in the absence of it • Microaerophile: does not grow at normal atmospheric concentrations of oxygen but requires a small amount of it in metabolism • Anaerobe: lacks the metabolic enzyme systems for using oxygen in respiration • Strict, or obligate, anaerobes: also lack the enzymes for processing toxic oxygen and cannot tolerate any free oxygen in the immediate environment and will die if exposed to it. • Aerotolerant anaerobes: do not utilize oxygen but can survive and grow to a limited extent in its presence

5. Carbon Dioxide • All microbes require some carbon dioxide in their metabolism • Capnophiles grow best at a higher CO2 tension than is normally present in the atmosphere

6. Physical Requirements for Growth • Temperature: • Psychrophiles: cold-loving microbes (-10 to 20 degrees C) • Mesophiles: moderate-temperature-loving microbes (10 to 50 degrees C) • Thermophiles: heat-loving microbes (40 to 73 degrees C) • Refrigeration severely retards the growth of most pathogenic bacteria

7. Psychrophile • A microorganism that has an optimum temperature below 15°C and is capable of growth at 0°C. • True psychrophiles are obligate with respect to cold and cannot grow above 20°C. • Psychrotrophs or facultative psychrophiles- grow slowly in cold but have an optimum temperature above 20°C.

8. Mesophile • An organism that grows at intermediate temperatures • Optimum growth temperature of most: 20°C to 40°C • Temperate, subtropical, and tropical regions • Most human pathogens have optima between 30°C and 40°C

9. Temperature and Growth Requirements [INSERT FIGURE 6.4]

10. Thermophile • A microbe that grows optimally at temperatures greater than 45°C • Vary in heat requirements • General range of growth of 45°C to 80°C • Hyperthermophiles- grow between 80°C and 120°C

11. Environmental Factors that Influence Microbes • Temperature Adaptations • Microbial cells cannot control their temperature, so they assume the ambient temperature of their natural habitat • The range of temperatures for the growth of a given microbial species can be expressed as three cardinal temperatures: • Minimum temperature: the lowest temperature that permits a microbe’s continued growth and metabolism • Maximum temperature:The highest temperature at which growth and metabolism can proceed • Optimum temperature: A small range, intermediate between the minimum and maximum, which promotes the fast rate of growth and metabolism • Some microbes have a narrow cardinal range while others have a broad one • Another way to express temperature adaptation- to describe whether an organism grows optimally in a cold, moderate, or hot temperature range

12. pH Requirements • pH: low pH = acidic, high pH = basic • pH range 0-14 • Normal growth range for bacteria is pH 6 to 8 (most bacteria can’t grow in orange juice) • Acidophiles (minority) can grow in pH 4 • Molds and yeasts grow in pH 4-6

13. Effects of pH • Majority of organisms live or grow in habitats between pH 6 and 8 • Obligate acidophiles • Euglena mutabilis- alga that grows between 0 and 1.0 pH • Thermoplasma- archae that lives in hot coal piles at a pH of 1 to 2, and would lyse if exposed to pH 7

14. Osmotic Pressure • Most microbes live either under hypotonic or isotonic conditions • Osmophiles- live in habitats with a high solute concentration • Halophiles- prefer high concentrations of salt • Obligate halophiles- grow optimally in solutions of 25% NaCl but require at least 9% NaCl for growth

15. Osmotic Pressure • Osmotic pressure: addition of salts to foods results in shrinkage of cell due to loss of water • Plasma membrane pulls away from cell wall which results in inhibition of cell growth • Ex. In food prep = salted fish, honey, sweetened and condensed milk (addition of high amounts of salt or sugar) • Halophiles: org. that can grow in high salt concentrations

16. Ecological Associations Among Microorganisms • Most microbes live in shared habitats • Interactions can have beneficial, harmful, or no particular effects on the organisms involved • They can be obligatory or nonobligatory to the members • They often involve nutritional interactions

17. Symbiosis • A general term used to denote a situation in which two organisms live together in a close partnership

18. Symbiosis • A general term used to denote a situation in which two organisms live together in a close partnership • Mutualism: when organisms live in an obligatory but mutually beneficial relationship

19. Symbiosis A general term used to denote a situation in which two organisms live together in a close partnership • Commensalism: the member called the commensal receives benefits, while its coinhabitant is neither harmed nor benefited • Satellitism: when one member provides nutritional or protective factors needed by the other

20. Symbiosis A general term used to denote a situation in which two organisms live together in a close partnership • Parasitism: a relationship in which the host organism provides the parasitic microbe with nutrients and a habitat

21. Nonsymbiotic Relationship • Organisms are free-living and relationships are not required for survival • Synergism: an interrelationship between two or more free-living organisms that benefits them but is not necessary for their survival • Antagonism: an association between free-living species that arrises when members of a community compete • One microbe secretes chemical substances into the surrounding environment that inhibit or destroy another microbe in the same habitat

22. Interrelationships Between microbes and Humans • Normal microbiotia: microbes that normally live on the skin, in the alimentary tract, and in other sites in humans • Can be commensal, parasitic, and synergistic relationships