Bacterial growth (L3)

• Methods to determine bacterial growth

  • Determination of cell number
  • Viable cell count
  • Determination of cell mass
  • Determination of cell constituents
• Total cell counts


  Using microscope (± stain)
• Coulter counter


  Method to determine cell number
• Viable cell count


  Grow, until we can see a colony by eye
• Dry weight measurement


  Method to determine cell mass
• Turbidity


  Method to determine cell mass
• Determination of cell constituents

  Measure specific cell material such as DNA
• Colony forming unit (CFU)


  A measure of viable cells in which a colony represents an aggregate of cells derived from a single progenitor cell
• Types of bacteria by temperature

  • Psycrophilic – <20°C
  • Mesophilic – 16-40°C
  • Thermophilic – > 40°C

  
• At low temps, bacteria become dormant
• At high temperatures, bacteria can be killed
• Nutrition types


  • Photoautotrophs
  • Photoheterotrophs
  • Chemoautotrophs or Lithotrophs
  • Chemoheterotrophs or heterotrophs
• Photoautotrophs


  Use light as energy source and CO2 as carbon source
• Photoheterotrophs


  Use light as energy source and organic compounds as carbon source
• Chemoautotrophs or Lithotrophs


  Use inorganic compounds (e.g. H2, NH3, NO2, H2S) as energy source and CO2 as carbon source
• Chemoheterotrophs or heterotrophs


  Use organic compounds as both energy and carbon source
• Essential elements for bacterial growth

  • Carbon
  • Oxygen
  • Nitrogen
  • Hydrogen
  • Phosphorus
  • Sulphur
  • Potassium
  • Magnesium
  • Calcium
  • Iron
• Growth factors


  Required in small amounts to fulfil specific roles in biosynthesis
• Types of growth factors

  • Purines and pyrimidines
  • Amino acids
  • Vitamins
• Auxotrophs


  Bacterial strains that need growth factors not needed by wild-type strains
• Water activity (AW)


  Denotes the water availability for microbial growth

  
• AW of pure water is 1.0
• Types of halophiles


  • Mild: 1-6%
  • Moderate: 6-15%
  • Extreme: 15-30%
• Osmophiles


  Organisms that survive in high sugar environments
• Xerophiles


  Organisms that live in dry environments
• Types of organisms by oxygen requirement

  • Obligate aerobes
  • Obligate anaerobes
  • Facultative anaerobes (or facultative aerobes)
  • Aerotolerant anaerobes
• All cells contain enzymes capable of reacting with O2, e.g. Oxidation of flavoproteins by O2 invariably result in the formation of H2 O2 and superoxide
• In aerobes, the potential for lethal accumulation of superoxide is prevented by superoxide dismutase
• Nearly all organisms contain catalase, which decomposes H2 O2
• Anaerobes lack superoxide dismutase and catalase and therefore undergo lethal oxidations by various oxygen radicals
• Types of bacteria by pH

  • Acidophiles
  • Neutrophiles
  • Alkaliphiles
• Binary Fission


  Growth of cells (usually lengthening), Duplication of chromosome, Septum synthesis and constriction, Cell divides into two identical daughter cells
• FtsZ


  Cell division protein that appears at the earliest moment of cell division and has a structural role in assembling at the site of septum
• Sporulation


  Process where vegetative cells form endospores when conditions for growth become harsh, involving activation of many genes. Endospores can remain dormant for years but can rapidly convert back to vegetative cells through germination.
• Endospore structure


  • Exosporium – protein covering
  • Spore coat – layers of spore specific proteins
  • Cortex – composed of loosely linked peptidoglycan and contains dipicolinic acid (DPA)
  • Core – contains usual cell wall, cytoplasmic membrane, nucleoid, and cytoplasm

  
• Major implications of bacterial growth and sporulation are in infection and sterilization/preservation