Ch 5 lecture

Ch 5 lecture - Chapter 5 - Environmental Influences and...

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Chapter 5 - Environmental Influences and Control of Microbial Growth Environmental factors that affect microbial growth Temperature Pressure Osmolarity (how much solute is in the area) pH Oxygen Temperature Temperature is a major environmental factor controlling microbial growth. Cardinal 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. Psychrophiles Cold: O°C–20°C Mesophiles 20°C–45°C Thermophiles 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 temperatures Proteins are more flexible compared to mesophiles or thermophiles Cryoprotectants can be used to preserve microbial cultures at low temperatures 10% DMSO (Dimethylsulfoxide) & 10% glycerol are commonly used in laboratories to preserve microbial cultures for long time in freezers. These cryoprotectants prevent ice crystals from forming, which c=would kill cells Mesophiles - mid range optimum temperature Found in Examples- most organisms you are familiar with such as Escherichia coli (found in the human intestine)
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Thermophiles Optimum temp above 40 degrees Celsius Some Archaea have been found growing at temps above 110 degrees Celsius Places thermophiles are found: soils subjected to full suntlight 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 temperatures 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 Help keep proteins from denaturing Induced by many stressful conditions: Heat High salt concentrations Arid conditions Pressure Barophiles Adapted to high pressures Up to 1,000 atm Barotolerant organisms Grow at high, but not very high pressure Tolerate the pressure, but do not prefer it Barosensitive organisms Die at high pressure Most “typical” bacteria, all mammals
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Osmolarity Water moves from areas of high water concentration to areas of lower water concentration. Water moves from areas of low solute concentration to areas of high solute
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This note was uploaded on 10/11/2011 for the course BIOL 2051 taught by Professor Brininstool during the Spring '07 term at LSU.

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Ch 5 lecture - Chapter 5 - Environmental Influences and...

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