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Unformatted text preview: TOP IC 3. M ICROBIAL GROWTH AND N UTR I T ION (Chapter 6) 1. REQU IREMENTS FOR GROWTH a) Microbial growth is an increase in the number of cells, not the size of the cells. b) Generally we look at the growth of populations, not individuals. c) Growth depends on physical and chemical requirements. A) PHYSICAL REQUIREMENTS i) Temperature (Figure 6.1 pg 156) a) Most microbes grow well at body temperature. b) Some grow at extremes: a. Psychrophiles - cold-loving. b. Psychrotrophs - prefer cold but can grow at warmer temps (food spoilage). c. Mesophiles - moderate-temperature-loving. d. Thermophiles - heat-loving (also hyperthermophiles and extreme thermophiles). b) Most bacteria grow only within a specific temperature range (Usually a small range): a. Minimum growth temperature - lowest temperature at which a species will grow. b. Optimum growth temperature - temperature at which it grows best (fastest). c. Maximum growth temperature - highest temperature at which growth is possible. ii) Ph a) Most bacteria grow best at a pH value near neutral, between 6.5 and 7.5. b) Some are acidophilic and grow in acid conditions, as low as pH1. iii) Osmotic pressure a) Microbes obtain most of the nutrients from the surrounding water and most must be grown in medium that is nearly all water. b) In a hypertonic solution, microbes undergo plasmolysis (cytoplasmic shrinkage) – prevents growth. c) Halophiles either need (obligate) or can tolerate (facultative) high salt concentrations. B. CHEMICAL REQUIREMENTS i) Carbon a) Carbon is the structural backbone of living matter and is needed for all compounds needed in a living cell. b) Chemoheterotrophs get carbon from organic molecule like protein, carbohydrates. c) Chemoautotrophs (chemo- and photo-) use CO 2 for C. ii) Nitrogen, Sulfur, Phosphorous, Trace elements a) Nitrogen is needed for protein and nucleic acid synthesis. b) N can be obtained from decomposition of proteins or from NH 4 + or NH 3- ; a few bacteria are capable of taking N 2 from the atmosphere (nitrogen fixation e.g Rhizobium)....
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