Environmental Factors

Tolerance to All Environmental Factors (Shelford’s Law of Tolerance)

• Temperature

• Solute Concentration / Water Activity

• pH (acidity versus alkalinity)

• Oxygen Concentration

• Barometric Pressure

• Electromagnetic Radiation

Cardinal TemperaturesMinimum, 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.

None

None

Rapid

SlowPsychrotrophs

Slow

Growth:

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.

•Neutrophiles: (5.5 -8.0); swap protons for K+.

•Alkalophiles: (8.5-10.5); swap protons for Na+; buffer compounds in cytoplasm.

•Acidophiles: (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 PressureBarotolerant 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.