文档介绍：Chapter4 Microbial growth
Environmental factors on growth
Growth in natural environment
Water availability, pH, temperature, oxygen concentration, pressure, radiation, and a number of other environmental factors influence microbial growth.
Yet many anisms, and particularly bacteria, have managed to adapt and flourish under environmental extremes that would destroy anisms.
Effect of environmental factors on growth
Bacteria grow over a range of temperatures; they do not reproduce below the minimum growth temperature nor above the maximum growth temperature. Within the temperature growth range there is an optimum growth temperature at which bacterial reproduction is fastest.
Effect of temperature on bacterial growth rate
anisms are classified as psychrophiles, mesophiles. thermophiles, and extremethemophiles based on their optimal growth temperature.
Temperature effect:
1. Psychrophile
(0-20oC)
2. Mesophile
(45-15oC)
3. Thermophile
(40-70oC)
4. Hyperthermophile
(65-95oC)
5. Extrem hyper-
thermophile
(80-120oC)
Temperature
A most important factor influencing the growth is the temperature sensitivity of enzyme catalyzed reactions.
High temperature:
Denature enzymes, transport carries, and other proteins.
Microbial membranes are also disrupted by temperature extremes.
The lipid bilayer melts and disintegrates.
Optimal growth temperature
Mesophiles:
human body temperature
pathogens
opportunists
pyschrophile
close to freezing
thermophile
close to boiling
Thermophile and Biotechnology
Enzymes from thermophiles are capable of catalyzing biochemical reactions at high temperature, they are more stable;
DNA polymerase, Taq polymerase, has been isolated from thermophile-Thermus aquaticus, for PCR application;
DNA polymerase, pfu polymerase, isolated from hyperthermophile-us furiosus, is more stable and useful for PCR application, it also less prone to errors;
Microbial process carried out at high T also eliminate or greatly reduce cooling costs.
Molecu