BIOL 2051_Ch. 5

BIOL 2051_Ch. 5 - Chapter 5 Environmental Influences and...

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Unformatted text preview: Chapter 5 - Environmental Influences and Control of Microbial Growth Environmental factors that affect microbial growth • Temperature • Pressure • Osmolarity (salt or sugar concentrations) • pH • Oxygen Temperature • Temperature is a major environmental factor controlling microbial growth. • Cardinal temperatures- minimum, optimum, & maximum temps for an organism • Minimum temperature - cellular processes slow; cytoplasmic membranes stiffen • Maximum temperature- proteins start to denature • Optimum temperature- organism grows best; between min & max • 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 enviroments • Example: Chlamydomonas- “snow algae” • Molecular adaptations of psychrophiles: • Membranes have high content of unsaturated fatty acids- semi fluid at low tempretures • Proteins are more flexiable compared to mesophiles or thermophiles • Cryoprotectants can be used to preserve microbial cultures at low temperatures • 10% BMSO (Dimethylsulfoxide) & 10% glycerol are commonly used in laboratories to preserve microbial cultures for long time in freezers. • Mesophiles- midrange optimum • Found in warm-blooded animals & many terrestrial & aquatic environments. • Examples- most organisms you are familiar with such as Escherichia coli (found in the human intestines. There are only two strains of pathogenic E. coli) • Thermophiles • Optimum temp above 40°C • Some archaea have been found growing at temps above 110°C • Places thermophiles are found: • 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 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 • 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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BIOL 2051_Ch. 5 - Chapter 5 Environmental Influences and...

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