FMB LEC FINALS: 1 - MICROBIAL GROWTH

• Microbial growth requirements


  • Physical
  • Chemical
• Physical requirements


  • Temperature
  • pH
  • Osmotic pressure
• Microorganisms classified by temperature range

  • Psychrophile
  • Psychrotroph
  • Mesophile
  • Thermophile

  
• Minimum growth temperature


  Lowest temperature at which the species will grow
• Optimum growth temperature


  Temperature at which the species grows best
• Maximum growth temperature


  Highest temperature at which growth is possible
• pH


  Acidity or alkalinity of a solution
• Most bacteria grow best in a narrow pH range near neutrality, between pH 6.5 and 7.5
• The optimum pH of molds and yeasts is generally below that of bacteria, usually about pH 5 to 6
• Osmotic pressure


  Microorganisms require water for growth, and high osmotic pressure can remove necessary water from a cell
• Plasmolysis


  The osmotic loss of water, or the shrinkage of the cell's cytoplasm
• Microbes adapted to high salt concentrations

  • Extreme halophiles (obligate halophiles)
  • Facultative halophiles
• If the osmotic pressure is unusually low (the environment is hypotonic), water tends to enter the cell rather than leave it, which can lyse some microbes with relatively weak cells

  
• Chemical requirements for microbial growth

  • Carbon
  • Nitrogen, Sulfur, and Phosphorus
  • Trace elements
  • Oxygen

  
• Carbon


  The structural backbone of living matter, needed for all organic compounds in a cell
• Nitrogen


  About 14% of the dry weight of a bacterial cell, obtained from decomposing protein-containing material, ammonium ions, or nitrates
• Phosphorus


  Needed for synthesis of nucleic acids, phospholipids, and ATP
• Sulfur


  Needed for synthesis of sulfur-containing amino acids and vitamins
• Trace elements


  Fe, Cu, Mo, Zn; cofactors for enzymes
• Microbes classified by oxygen requirements

  • Obligate aerobe
  • Facultative anaerobe
  • Anaerobe

  
• Singlet oxygen


  Normal molecular oxygen boosted into a higher-energy state, extremely reactive
• Superoxide radicals


  Formed in small amounts during normal respiration, toxic to cellular components
• Superoxide dismutase (SOD)


  Enzyme that converts superoxide radicals into molecular oxygen and hydrogen peroxide
• Catalase


  Enzyme that converts hydrogen peroxide into water and oxygen
• Peroxidase


  Enzyme that converts hydrogen peroxide into water
• Hydroxyl radical


  Highly reactive intermediate form of oxygen, formed by ionizing radiation
• Other oxygen-related microbes


  • Aerotolerant anaerobes
  • Microaerophiles
• Organic growth factors


  Essential organic compounds an organism is unable to synthesize, must be obtained from the environment (e.g. vitamins, amino acids, purines, pyrimidines)
• Microbial growth requirements


  • Physical requirements
  • Chemical requirements
• Physical requirements


  • Temperature
  • pH
  • Osmotic pressure
• Microorganisms classified by temperature range

  • Psychrophile
  • Psychrotroph
  • Mesophile
  • Thermophile

  
• Minimum growth temperature


  Lowest temperature at which the species will grow
• Optimum growth temperature


  Temperature at which the species grows best

  
• Maximum growth temperature


  Highest temperature at which growth is possible
• Most bacteria grow best in a narrow pH range near neutrality, between pH 6.5 and 7.5
• The optimum pH of molds and yeasts is generally below that of bacteria, usually about pH 5 to 6
• Osmotic pressure


  High osmotic pressure has the effect of removing necessary water from a cell
• Plasmolysis


  The osmotic loss of water, or the shrinkage of the cell's cytoplasm
• Microbes adapted to high salt concentrations

  • Extreme halophiles (obligate halophiles)
  • Facultative halophiles
• Hypotonic environment


  Water tends to enter the cell rather than leave it