3. Microbial Growth

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  1. exponential growth
    N= N0 x 2n

    • N= final cell number
    • N0 = initial cell number
    • n = number of generations
  2. generation time (doubling time)
    g = t/n

    t = time elapsed during exponential growth
  3. batch culture
    • closed system of a fixed volume where bacterial growth alter environment
    • 1) lag phase
    • 2) log phase
    • 3) stationary phase
    • 4) death phase
  4. Lag phase
    • when a stationary phase culture is diluted into fresh medium or when cells transferred from rich to minimal medium
    • must synthesize proteins for rapid growth or specific proteins needed to produce nutrients not in culture medium
  5. stationary phase
    • growth is limited
    • run out of essential nutrient or accumulate toxic waste product
    • no net change in cell number
    • some processes can continue
    • sigma s protein controls response to stresses
  6. chemostat
    open system maintained in chemically constant environment

    • dilution rate = fraction of volume replaced per time
    • too fast - culture washes out, cell division can't keep up
    • too slow - nutrient isn't supplied fast enough

    • increase nutrient concentration - growth rate and yield affected, then only yield affected
    • total yield determined by most limiting nutrient
  7. rich/complex medium
    contains complex organic molecules
  8. defined or minimal medium
    contains precise amounts of known chemicals
  9. autotrophs
    • can get all of the C they need to build structures from CO2
    • can gain energy from photons or by oxidizing inorganic compounds
  10. heterotrophs
    • require an organic C source
    • most use NH3- or NO3- as nitrogen source
    • only nitrogen-fixing bacteria can use N2
  11. obligate aerobes
    must use O2 as an electron receptor in respiration
  12. anaerobe
    must avoid O2
  13. facultative anaerobe
    can use O2 in respiration or use other metabolic strategies
  14. microaerophile
    require low O2 concentration
  15. aerotolerant
    • ignore O2
    • only ferment
  16. reactive oxygen species
    • cause cell damage
    • superoxide radical union
    • hydrogen peroxide
    • hydroxyl radical

    • enzymes remove toxic oxygen species
    • superoxide dismutase
    • catalase
    • peroxidase
  17. problems of high temperature thermophiles
    • critical enzymes are denatured
    • membranes too fluid and cannot maintain barrier
  18. solutions to problems of high temperature thermophiles
    • proteins are more stable because contain fewer glycine residues and N-termini H-bonded to rest of protein
    • synthesize chaperones to refold
    • synthesize phospholipids with saturated fatty acids, pack tightly to form membrane
  19. problems of low temperature psychrophiles
    • not much thermal motion, perform reactions slow
    • membrane fluidity decreases, inhibits function of critical proteins
  20. solutions to problems of low temperature psychrophiles
    • proteins are more flexible
    • phospholipids with highly unsaturated fatty acids, remain mobile
  21. hypotonic medium (solute concentration less than in cytoplasm)
    • water enters the cell
    • bacteria have rigid cell walls, prevent lysis
    • mechanosensitive channels can leak specific solutes out
  22. hypertonic medium (solute concentration greater than cytoplasm)
    • water exits the cell
    • can synthesize/import compatible solutes
  23. compatible solutes
    small molecules or ions that do not disrupt cell metabolism, increase internal osmolarity, help retain water
  24. halophiles
    • bacteria that require high NaCl concentration for growth
    • proteins adapted because use K+ as compatible solute
  25. acidophiles/alkaliphiles
    • membranes are more impermeant to protons
    • ether-linked lipids are less leaky and more resistant to acid hydrolysis
  26. acidophiles
    expend energy to scavenge protons from environment using Na+/H+ antiporters, use membrane gradient of Na+ to drive flagellar rotation, nutrient uptake because H+ is limiting
Card Set:
3. Microbial Growth
2011-10-03 04:55:34
PMB 112 midterm1

general microbiology midterm 1
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