05 Environmental Control of Growth.pptx - Environmental Limits on Microbial Growth • • • • • Temperature Pressure Osmolarity Oxygen pH Factors

05 Environmental Control of Growth.pptx - Environmental...

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Environmental Limits on Microbial Growth Temperature Pressure Osmolarity Oxygen pH
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Factors Affecting Bacterial Growth Rates Temperature Cardinal temperatures Minimum temperature below which no growth occurs Optimum temperature at which growth is most rapid Maximum temperature above which no growth occurs Cardinal temperatures vary for different organisms
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Factors Affecting Bacterial Growth Rates
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Temperature Classes of Microorganisms Psychrophiles Optimum temperature < 15 o C Minimum temperature < 0 o C Maximum temperature < 20 o C Found in polar regions of Earth, in and under ice Ex.: snow alga Chlamydomonas nivalis
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Temperature Classes of Microorganisms Psychrotolerant Optimum temperature < 20-40 o C Minimum temperature < 0 o C Maximum temperature < 45 o C Can be isolated from foods in refrigerators Includes numerous bacteria, fungi and algae
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Temperature Classes of Microorganisms Mesophiles Optimum temperature < 39 o C Minimum temperature < 10 o C Maximum temperature < 48 o C Found in microbial flora of mammals, in temperature habitats Ex: E. coli
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Temperature Classes of Microorganisms Thermophiles Optimum temperature > 45 o C Minimum temperature < 40 o C Maximum temperature < 68 o C Found in extreme habitats Hot springs Oceanic thermal vents Includes many species of Archaea
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Temperature Classes of Microorganisms Hyperthermophiles Optimum temperature > 80 o C Minimum temperature < 65 o C Maximum temperature > 100 o C Found in extreme habitats Hot springs Oceanic thermal vents Includes many species of Archaea
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Response to Temperature 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
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Variations in 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
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Changes in Water Activity Halophiles Require high concentration of NaCl 2–4 M (10x seawater) Live in salt seas
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