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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 Growth: An average day in your ‘frig. None Slow Rapid Slow Psychrotrophs None 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. •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 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.