Mic 101 Lecture 4-5 Growth

Mic 101 Lecture 4-5 Growth - Mic 101. Lectures 4-5....

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Mic 101. Lectures 4-5. Microbial Growth I. Growth of Bacteria in Nature. In general, bacteria are ubiquitous in nature, except in the absence of water, where propagules can survive, but not grow. A. Physicochemical factors are selective of specific groups. e.g. 1. Temperature: psychrophiles, mesophiles and thermophiles. Most pathogens are mesophiles with an optimal temperature for growth around 37 o C 2. Osmotic pressure and/or salt concentration. Osmotic pressure is expressed as water activity (a w ). Pure water has an activity of 1.0. The addition of solutes reduces the activity; for examples: human blood has an a w of 0.995, seawater 0.98, salami 0.85 and dried fruit 0.70. When water activity is dictated by salt, the microbial growth response is termed halo, as is halophile, of which there are degrees, as opposed to nonhalophile. Vibrio cholera is halotolerant. Halobacterium halobium (gives the red color to salt evaporation ponds in the South San Francisco Bay) is an extreme halophile with an a w of 0.75. 3. Oxygen. There are two ways to look at oxygen, its presence or absence and its biological requirement or production or not. Then one can consider oxygen derivatives. Presence = oxic; absence = anoxic; small quantities = microoxic. Required for growth = aerobic; not required for growth = anaerobic. Biologically, oxygen is produced only by photosynthesis. Cyanobacterial and plant photosynthesis is called oxygenic (produced). Purple and green photosynthetic bacterial photosynthesis is called anoxygenic (not produced).
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Mic 101. Lectures 4-5. Microbial Growth B. Growth of populations and communities in nature. 1.
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This note was uploaded on 04/16/2010 for the course MIC MIC taught by Professor Meek during the Spring '10 term at UC Davis.

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Mic 101 Lecture 4-5 Growth - Mic 101. Lectures 4-5....

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