Environmental%20Factors%20Tolerance%20to%20All%20Environmental%20Factors%20(Shelford

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Environmental FactorsTolerance to All
Environmental Factors (Shelfords Law of
Tolerance)

• Temperature
• Solute Concentration / Water Activity
• pH (acidity versus alkalinity)
• Oxygen Concentration
• Barometric Pressure
• Electromagnetic Radiation

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Cardinal TemperaturesMinimum, Optimum, and
Maximum
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An average day in your frig. Food items cool
more rapidly in a shallow container due to
greater surface to volume ratio.
Growth
None
Slow
Rapid
Slow
Psychrotrophs
None
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Water Activity Quantifies water availability in
an environmentdecreases with increasing solute
concentration.
Plasmolysis hypertonic solutions cytoplasm
water loss compatible solutes. Osmotolerant
grows over a wide range of water activity fungi
gt bacteria. Halophile salt-loving requires gt
0.2M sodium chloride.
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• All prokaryotes begin to die at intracellular pH
  lt 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.

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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.
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Barometric PressureBarotolerant versus
BarophilesMembranes are very fluid (unsatuated
short-chain fatty acids)
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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.