MICRO CH5 - Chapter 5 Environmental Influences and Control...

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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 in environment pH Oxygen Temperature Temperature is a major environmental factor controlling microbial growth. Incubation (different temperatures) Cardinal Minimum temperature - cellular processes slow; cytoplasmic membranes stiffen so transport of nutrients in and waste out occurs much more slowly; not happy but can survive Maximum temperature- proteins start to denature; just above max temp, cell will die Optimal temperature - organism grows best; between min & max; important for incubation M inimum: membrane gelling; transport processes so slow that growth cannot occur Optimum: enzymatic reactions occur at max possible rate Max: protein denaturation; cell will eventually lyse Microorganisms can be grouped by the temperature ranges they require. Psychrophiles: Cold: O°C–20°C Mesophiles: used in lab 20°C–45°C Thermophiles (hot places) 40°C–80°C Extreme thermophiles (very hot places); also called hyperthermophiles 65°C–113°C Strain 121: 121 degrees Celcius Psychrophiles - found in constantly cold environments Example: Chlamydomonas- “snow algae”; pink, grows in the snow, makes the snow pink Bacteria can actively grow in sea ice
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Molecular adaptations of psychrophiles: Membranes have high content of unsaturated fatty acids—CM is semi- fluid at low temperatures; don’t gel as quickly Proteins are more flexible compared to mesophiles or thermophiles Amino acids are a little different in concentration 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 - midrange optimum temperature Examples- most organisms you are familiar with such as Escherichia coli (found in the human intestine) Everything used in lab Thermophiles Optimum temp above 40 degrees C Some archaea have been found growing at temps above 110 degrees C; 121 is highest (ocean floor, a lot of pressure, hydrothermal vents) Places thermophiles are found: soils subjected to full sunlight fermenting materials (compost, turns into gardening soil by microorganisms) 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. PCR
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MICRO CH5 - Chapter 5 Environmental Influences and Control...

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