Download Bacterial Nutrition & Growth

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Environmental Factors
Tolerance to All Environmental Factors
(Shelford’s Law of Tolerance)
Solute Concentration / Water Activity
pH (acidity versus alkalinity)
Oxygen Concentration
Barometric Pressure
Electromagnetic Radiation
Cardinal Temperatures
Minimum, Optimum, and Maximum
An average day in
your ‘frig.
Food items cool more
rapidly in a shallow
container due to greater
surface to volume ratio.
Water Activity
Quantifies water availability in an environment;
decreases with increasing solute concentration.
Plasmolysis: hypertonic solutions; cytoplasm water loss; compatible solutes.
Osmotolerant: grows over a wide range of water activity; fungi > bacteria.
Halophile: “salt-loving”; requires > 0.2M sodium chloride.
• All prokaryotes
begin to die at
intracellular pH < 5.
(5.5 -8.0); swap
protons for K+.
(8.5-10.5); swap
protons for Na+;
buffer compounds
in cytoplasm.
(0-5.5): extreme
control over
generating ATP.
Oxygen Requirement Types
2 to 10% atm O2
Super Oxide Dismutase (SOD): superoxide radicals go to hydrogen peroxide & O2.
Catalase: hydrogen peroxide go to water & O2.
Barometric Pressure
Barotolerant versus Barophiles
Membranes are very fluid
(=unsatuated short-chain fatty acids)
Electromagnetic Radiation
• Shorter wavelengths are
higher energy.
• Ionizing radiation:
Gamma & X-Rays; OH·;
sterilizing plastics.
• Ultraviolet radiation:
DNA damage at 265nm;
sterilizing surfaces &
water treatment.
• Visible light (PAR):
photosynthetic energy;
bacterial pigments get
excited; transfer energy
to O2 to form singlet
oxygen; cell damage.