Growth rate increases with temperature psychrophiles

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Growth rate increases with temperature • Psychrophiles –Cold: O°C–20°C • Mesophiles –12°C–45°C • Thermophiles –40°C–80°C Extreme thermophiles –65°C–113°C Microbial proteins are adapted to the habitat temperature
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Water Activity Water is the most important factor controlling the growth of microorganisms Osmolarity: the number of solute molecules in a solution High osmolarity reduces the water activity • Hypotonic environment Higher solute concentration than the cytoplasm Water coming into the cell – burst cell membrane Cell wall • Hypertonic environment Lower solute concentration than the cytoplasm Water flowing out of the cell • Plasmolysis Osmolytes – Compatible solutes to increase intracellular osmolarity
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Oxygen Aerobes: able to grow in the presence of O 2 Obligate aerobes: can not grow without O 2 Anaerobes: can grow in the absence of O 2 Aerotolerant anaerobes: can grow in O 2 , but can not utilize it Obligate anaerobes: growth is inhibited by O 2 Anaerobic organisms are often found in aquatic environments because O 2 is weakly soluble Micro-aerophiles: Grow only at low O 2 levels (< 10%) Facultative Aerobes: Can grow aerobically or anaerobically Aerobic growth is more energy-efficient
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Obligate Aerobe Obligate Anaerobe Facultative Aerobe Micro- aerophile Aerotolerant Anaerobe
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