1. 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

2. Cardinal Temperatures Minimum, Optimum, and Maximum

3. 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:

4. 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.

5. 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.

6. 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.

7. Barometric Pressure Barotolerant versus Barophiles Membranes are very fluid (=unsatuated short-chain fatty acids)

8. 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.