Ch6Notes - Chapter 6-Microbial Growth I. Microbial growth =...

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Chapter 6—Microbial Growth I. Microbial growth = increase in number of cells, not cell size. a. Physical Requirements: i. Temperature. Fig. 6.1. 1. Minimum growth temperature = lowest temperature at which a species will grow. 2. Optimum growth temperature = temperature at which a species will grow best. 3. Maximum growth temperature = highest temperature at which growth is possible. 4. Psychrophiles are cold loving microbes that can grow at 0°C but grow optimally around 15°C. a. Found deep in the ocean or in polar regions. 5. Psychrotrophs are also cold loving microbes. a. Grow at 0°C but optimally at 20-30°C. b. Cause food spoilage because they are common and grow well in refrigerators. 6. Mesophiles are moderate temperature loving microbes. a. Grow optimally between 25-40°C. b. Most common types of microbes. Many organisms that grow inside animals fall into this group. c. Includes many common spoilage and disease organisms. i. When large amounts of food are to be refrigerated, the time necessary for adequate cooling can allow bacteria to grow to high numbers. Figs. 6.2, 6.3. 7. Thermophiles are heat loving microbes. a. Many grow optimally between 50-60°C. 8. Archaean hyperthermophiles (extreme thermophiles) grow optimally at temperatures up to 80°C or greater. a. Found in geothermal hot springs and vents. b. Deep ocean hydrothermal vents have bacterial populations that can survive temperatures of about 110°C; [pressure vs. boiling point]. ii. pH: 1. Most bacteria grow between pH 6.5 and 7.5. a. In the lab, bacteria often produce acids that can inhibit their own growth with increasing [H + ]. 2. Molds and yeasts grow between pH 5 and 6. 3. Acidophiles grow in acidic environments. iii. Osmotic Pressure. Fig. 6.4. 1. When a microbe is suspended in a hypertonic solution, water moves out of the cell via osmosis. a. This causes plasmolysis = shrinkage of the cell’s cytoplasm. i. This can permanently damage the plasma membrane. b. Growth is inhibited as the plasma membrane pulls away from the cell wall. c. Salted meats, honey, and sweetened condensed milk are preserved via this mechanism. i. Extreme and obligate halophiles require high salt concentrations in order to grow. ii. Facultative halophiles do not require high salt concentrations, but can grow in salt concentrations up to 2%, which inhibits the growth of many microbes. 2. When a microbe is suspended in a hypotonic solution, water enters the cell via osmosis. If the microbe has a relatively weak cell wall, it may lyse.
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b. Chemical Requirements: i. Carbon: 1. Used to make structural organic molecules and energy rich molecules. 2.
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This note was uploaded on 11/05/2010 for the course BIOL 211 taught by Professor Paxton during the Fall '10 term at Salem College.

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Ch6Notes - Chapter 6-Microbial Growth I. Microbial growth =...

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