Environmental Factors Tolerance to All Environmental Factors (Shelford’s Law of Tolerance) Temperature Solute Concentration / Water Activity pH (acidity.

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Presentation transcript:

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 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. None Rapid Slow Psychrotrophs 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: ( ); swap protons for K+. Alkalophiles: ( ); swap protons for Na+; buffer compounds in cytoplasm. Acidophiles: (0-5.5): extreme control over generating ATP.

Oxygen Requirement Types 2 to 10% atm O 2 Super Oxide Dismutase (SOD): superoxide radicals go to hydrogen peroxide & O 2. Catalase: hydrogen peroxide go to water & O 2.

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 O 2 to form singlet oxygen; cell damage.