Section 5.4 Growth is measured by the change in the number of cells with time. Measurements of turbidity are indirect, but very useful, measures of cell numbers. Describe how you would dilute a bacterial culture by 10 -7 . In a chemostat, the rate at which the culture is diluted governs the growth rate and the population size is governed by the concentration of the growth-limiting nutrient entering the vessel. Section 5.7 Temperature is a major environmental factor controlling microbial growth.
Various microorganisms differ greatly in their temperature requirements for growth.
Escherichia coli can grow at a higher temperature in complex than in defined medium. Section 5.8 Organisms with cold temperature optima are called psychrophiles, and the most extreme examples inhabit permanently cold environments. Psychrophiles have evolved biomolecules that function best at cold temperatures, but that are unusually sensitive to warm temperatures. These organisms inhabit hot environments up to and including boiling hot springs, as well as undersea hydrothermal vents that can have temperatures in excess of 100 C. Thermophiles and hyperthermophiles produce heat stable macromolecules. The acidity or alkalinity of an environment can greatly affect microbial growth.