Wednesday Notes

Microbial Nutrition & Growth

Elements Essential for Growth:

  • Carbon
  • Oxygen
  • Nitrogen
  • Hydrogen
  • Phosphorus
  • Sulfur
  • + Magensium, Calcium, Iron, Zinc (co-factors for enzymes)
  • + some other trace elements → used in “membrane pumps” (proteins that transfer ions. Also, used to maintain water balance.)

Oxygen Requirement Terms:

Obligate aerobes – must have oxygen in order to conduct metabolic RXNs, such as respiration. (These would be found at the top of a broth tube)

Obligate anaerobes – must live in an environment w/ no oxygen in order to conduct metabolic RXNs (ex. Clostridium botulinum)

Facultative anaerobes – prefer/live best in aerobic environments but can maintain metabolic processes in anaerobic environment. (ex. yeast)

Aerotolerant anaerobes – same as obligate anaerobes but oxygen doesn’t kill them.

Microphiles – Requires a little oxygen.

Toxic Form of Oxygen:

Singlet Oxygen 1O2 : Molecular oxygen that has been boosted to a higher energy state making it extremely reactive.

Superoxide Radical O2 : formed in small amounts during aerobic respiration, highly toxic.

Peroxide anion O2 2-: Produced during RXN beneath. The Superoxide Radical O2 acts as the catalyst for the reaction.

\mathrm{2\ O_2 ^-\ +\ 2\ H^+\ \xrightarrow {SOD}\ \ H_2O_2 +\ O_2}
Formation of hydrogen peroxide by superoxide dismutase (SOD)

Hydroxyl radical: OH

Important enzymes that react with the toxic forms of Oxygen listed above, to detoxify the Oxygen radical/ion.

(Note: Brahce said to focus more on the enzymes that react with the oxygen’s rather than the oxygen structures)

  1. Superoxide dismutase: Detoxifies superoxide radical
  2. Peroxidase: Detoxifies hydrogen peroxide (H2O2) and Superoxide Radical (O2 2¯)
  3. Catalase: Also helps the superoxide dismutase remove the superoxide radical by catalyzing the reaction for peroxide anion. (confusing)

Organism Temperature Requirements:

  1. Psychrophiles – “Cold-loving” (near freezing temps.)
  2. Mesophiles – “Middle-temp-loving” (room temps)
  3. Thermophiles – “Heat-loving” (Hot environments)
  4. Hyperthermophiles – “Extreme-heat-loving” (near boiling temps)

Other Requirements for growth:

pH: most human pathogens grow best around neutral pH (buffers added to growth media to maintain pH)

Note – Fungi grows best in somewhat acidic conditions (6-7 pH range)

Osmotic pressure: most human pathogens grow best in isotonic conditions exceptions include Staphylococcus

◊ Growth of a bacteria population is exponential: meaning as time continues so does cell growth.

Bacteria Life Phases:

Lag Phase: bacterial cells are preparing for growth by replicating chromosomes & making extra cell material (peptidoglycan, etc) for splitting in 1/2 (binary fission)

Log Phase: most of the growth occurs; binary fission occurs (1 cell → 2 cell)

Stationary Phase: amount of cell reproduction is equal to the amount of death.

Death Phase: # of cells dying is > (is greater) than # of cells being produced (this is due to lack of nutrients and waste buildup)





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