Chapter+5 - Chapter 5 Environmental In fluences and Control...

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Chapter 5 - Environmental Influences and Control of Microbial Growth Environmental factors that affect microbial growth Temperature Pressure Osmolarity pH Oxygen Temperature Temperature is a major environmental factor controlling microbial growth. Minimum temperature - cellular processes slow; cytoplasmic membranes stiffen Maximum temperature- proteins start to denature Optimum temperature - Microorganisms can be grouped by the temperature ranges they require. Psychrophile Cold: O°C–20°C Mesophile 20°C–45°C Thermophile 40°C–80°C Extreme thermophiles 65°C–113°C Psychrophiles - found in constantly cold environments Example: Chlamydomonas- “snow algae” Molecular adaptations of psychrophiles: Membranes have high content of unsaturated fatty acids – semi-fluid at low temp Proteins are more flexible compared to mesophiles or thermophiles Cryoprotectants can be used to preserve microbial cultures at low temps 10% DMSO (Dimethylsulfoxide) & 10% glycerol are commonly used in laboratories to preserve microbial cultures for long time in freezers. Mesophiles - mid-range optimum temp Examples- most organisms you are familiar with such as Escherichia coli (found in the human intestines) Thermophiles Optimum temp above 40 C Some archaea have been found growing at temps above 110 C Places thermophiles are found:
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soils subjected to full sunlight fermenting materials (compost piles) hot springs Thermus aquaticus is a common hot spring thermophile. The heat stable DNA polymerase from this bacterium is mass produced and used in laboratories to replicate DNA in a test tube. Molecular adaptations of thermophiles: Membranes have a high content of saturated fatty acids – stable and functional at high temperature Enzymes are heat stable- proteins are more rigid compared to mesophiles or psychrophiles Heat shock response Occurs at high end of temperature range “emergency” proteins produced (molecular chaperones hold them together so they can’t unfold) Help keep proteins from denaturing Induced by many stress conditions Heat High salt concentrations Arid conditions Pressure Barophiles Adapted to high pressure Up to 1,000 atm Barotolerant organisms Grow at high, but not very high pressure Barosensitive organisms Die at high pressure Most “typical” bacteria, all mammals Osmolarity Water moves from areas of high water concentration to areas of lower water
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Chapter+5 - Chapter 5 Environmental In fluences and Control...

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