Microbiology: Microbial Temperature Classifications PDF

Microbes can be classified based on the temperatures they can grow in: Optimum Growth Temperature: The best temperature for growth. Minimum Growth Temperature: The lowest temperature for survival and replication. Maximum Growth Temperature: The highest temperature for growth. Imp...

Microbes can be classified based on the temperatures they can grow in: Optimum Growth Temperature: The best temperature for growth. Minimum Growth Temperature: The lowest temperature for survival and replication. Maximum Growth Temperature: The highest temperature for growth. Important Information: Lake Whillans Exploration: ○ Researchers expected little life due to cold and nutrient-poor conditions. ○ Found abundant microbial life. Deep-Sea Vents: ○ Host bacteria that thrive at very high temperatures (up to 340 °C). Microbial Temperature Classifications: ○ Mesophiles: Prefer moderate temperatures (20 °C to 45 °C). Include human microbiota and pathogens (e.g., E. coli, Salmonella). ○ Psychrotrophs (Psychrotolerant): Prefer cooler temperatures (4 °C to 25 °C). Found in temperate climates and spoil refrigerated food. Psychrophiles (cold-loving organisms): Grow at 0 °C and below, optimal growth around 15 °C. Usually do not survive above 20 °C. Found in permanently cold environments (e.g., deep ocean waters). Important decomposers in cold climates. Thermophiles (heat-loving organisms): Grow optimally at 50 °C to a maximum of 80 °C. Do not multiply at room temperature. Common in hot springs, geothermal soils, and compost piles. Examples: Thermus aquaticus, Geobacillus spp. Hyperthermophiles: Grow between 80 °C and 110 °C, with some surviving above 121 °C. Found in extreme environments like hydrothermal vents (up to 340 °C). Examples: Pyrobolus, Pyrodictium. Adaptation to Extreme Temperatures: Low temperatures cause: ○ Loss of membrane fluidity and ice damage.  ○ Slowed chemical reactions. ○ Rigid proteins that may denature. High temperatures cause: ○ Denaturation of proteins and nucleic acids. ○ Increased fluidity that impairs metabolism. Applications of heat effects include sterilization and pasteurization. Psychrophiles' Protein Characteristics: Proteins are more flexible and have fewer stabilizing bonds. Contain antifreeze proteins and unsaturated lipids for membrane fluidity. Growth rates are slower than at moderate temperatures. Can survive freezing and be stored with glycerol at -80 °C. Thermophiles' and Hyperthermophiles' Macromolecule Differences: Higher ratio of saturated lipids to limit membrane fluidity. DNA has more guanine-cytosine pairs for stability. Proteins have additional bonds and modified amino acids for resistance to denaturation. Practical Applications: Thermoenzymes from thermophiles are used in PCR (e.g., Taq polymerase). Enzymes from thermophiles are used in hot-water detergents for better effectiveness.