Mic 201 Lecture

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Mic 201 Lecture 12 Outline Environmental
Effects on Microbial Growth

• Factors that play a role in controlling
  microbial growth.
• Temperature. How does temperature affect growth?
• Cardinal temperatures minimum, optimum and
  maximum growth temperature.
• Which are the factors that control an organism
  minimum and maximum growth temperature?
• Classification of microorganisms according to
  their growth temperatures.

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• Microbial growth at cold temperatures
• Psychrophilic and psychrotolerant
  microorganisms.
• Molecular adaptations to psychcrophily
• Microbial growth at high temperatures
• Termophiles and hyperthermophiles.
• Molecular adaptations to thermophily.
• Microbial growth at low and high pH.
• Osmotic effects on microbial growth.
• Oxygen and microbial growth.
• Classification of microorganisms according to
  their oxygen needs.

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Factors that play a role in controlling microbial
growth.

• temperature

• pH

• Water availability

• oxygen

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Temperature. How does temperature affect growth?
Reaction speed Denaturation
Cardinal temperatures minimum, optimum and
maximum growth temperature.
Which are the factors that control an organism
maximum growth temperature?
What about minimum temperatures?
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Classification of microorganisms according to
their growth temperatures.

• psychrophiles

• mesophiles

• thermophiles

• hyperthermophiles

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A field of pink snow in the alpine Sierra Nevada
of central California due to snow algae
(Chamydomonas nivalis
Packs of pink snow are a common sight during
summer on alpine slopes of California's Sierra
Nevada. (Taken near the Dana Plateau in Yosemite
National Park at about 12,000 feet elevation).
Compressing pink snow with your boot increases
the density of the red cells and heightens the
color.
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Microbial growth at cold temperatures Psychrophil
ic and psychrotolerant microorganisms. Molecular
adaptations to psychcrophily
Cold environments are not sterile
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Molecular adaptations to psychrophily
Greater alfa-helix content in proteins. Greater
polar and lesser hydrophobic amino acid
content Active transport optimal at low
temperature. Membranes with a higher content of
unsaturated fatty acids.
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Extremophiles (bacteria not the professor!).
Bacteria in hot springs
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Extremophiles Cyanobacteria in Yellowstone
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Microbial growth at high temperatures Termophiles
and hyperthermophiles.
Thermophiles optimum growth temperature is above
45 0C. Hyperthermophiles optimum growth
temperature is above 80 0C.
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Molecular adaptations to thermophily.
Enzymes and other proteins are most stable at
high temperatures. Change in one critical amino
acid? Membranes rich in saturated fatty
acids. Lipid monolayer in Archaea (no fatty
acids).
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Microbial growth at low and high pH
Acidophiles organisms that grow best at low
pHs. Obligate acidophiles. Cytoplasmic membranes
stable at low pHs. Alkaliphiles grow best at
high pHs.
Can a proton motive force be established when the
external surface of the membrane is so alkaline?
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Osmotic effects on microbial growth
Water availability is measured in terms of water
activity.
Halophiles, extreme halophiles,
halotolerants. Mild halophiles low (1-5) NaCl
requirement. Moderate halophiles moderate
(6-15) NaCl requirement. Extreme halophiles
15-30 NaCl
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Oxygen and microbial growth. Classification of
microorganisms according to their oxygen needs.
Aerobes. Microaerophiles. Facultative
aerobes. Anaerobes aerotolerant anaerobes and
strict (obligate) anaerobes.