C. Factors that Influence Bacterial Growth
LEARNING OBJECTIVES FOR THIS SECTION
Factors Influencing Bacterial Growth
1. Physical requirements
Bacteria have a minimum, optimum, and maximum temperature for growth and can be divided into 3 groups based on their optimum growth temperature:
1. Psychrophiles (def) are cold-loving bacteria. Their optimum growth temperature is between -5C and 15C. They are usually found in the Arctic and Antarctic regions and in streams fed by glaciers.
2. Mesophiles (def) are bacteria that grow best at moderate temperatures. Their optimum growth temperature is between 25C and 45C. Most bacteria are mesophilic and include common soil bacteria and bacteria that live in and on the body.
3. Thermophiles (def) are heat-loving bacteria. Their optimum growth temperature is between 45C and 70C and are comonly found in hot springs and in compost heaps.
4. Hyperthermophiles (def) are bacteria that grow at very high temperatures. Their optimum growth temperature is between 70C and 110C. They are usually members of the Archae and are found growing near hydrothermal vents at great depths in the ocean.
b. Oxygen requirements
Microorganisms show a great deal of variation in their requirements for gaseous oxygen. Most can be placed in one of the following groups:
1. Obligate aerobes (def) are organisms that grow only in the presence of oxygen. They obtain their energy through aerobic respiration (def).
2. Microaerophiles (def) are organisms that require a low concentration of oxygen (2% to 10%) for growth, but higher concentrations are inhibitory. They obtain their energy through aerobic respiration (def).
3. Obligate anaerobes (def) are organisms that grow only in the absense of oxygen and, in fact, are often inhibited or killed by its presense. They obtain their energy through anaerobic respiration (def) or fermentation (def).