Microbial Nutrition & Growth
Elements Essential for Growth:
- + 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.
- 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)
- Superoxide dismutase: Detoxifies superoxide radical
- Peroxidase: Detoxifies hydrogen peroxide (H2O2) and Superoxide Radical (O2 2¯)
- Catalase: Also helps the superoxide dismutase remove the superoxide radical by catalyzing the reaction for peroxide anion. (confusing)
Organism Temperature Requirements:
- Psychrophiles – “Cold-loving” (near freezing temps.)
- Mesophiles – “Middle-temp-loving” (room temps)
- Thermophiles – “Heat-loving” (Hot environments)
- 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)