Chapter 6:
Microbial
Growth
Requirements for Growth
• Physical Requirements
– Temperature
– pH
– Osmotic Pressure
• Chemical Requirements
– Carbon
– Nitrogen,Sulfur, Phosphorus
– Oxygen
Temperature
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• Psychrophiles: cold-loving
– Mostly in ocean’s depths (not common)
– Can grow 0°, optimal at 15°
• Psychrotrophs
– Low temperature food spoilage bacteria
– Can grow 0°, optimal 20-30°
Artic Sea bacteria:
Strain34h, stained fluorescent
blue for better viewing.
• Mesophiles: moderate-temp-loving
– Optimal 25-40°
– Most common microbes, spoilage and
disease
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E. coil
Temperature
Thermophiles: heat-loving
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– Optimal 50-60°
– Important in compost piles
Hyperthermals: extreme
thermophiles
SEM of a thermophilic Bacillus
species isolated from a compost pile at 55°
– Optimal 80°+
– Hot springs, volcanoes
How do they tolerate the high
temperatures?
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• cell membranes don’t contain fatty acids
• special enzymes fold their DNA into special heatstable coils
• enzymes themselves are heat stable with extra
bonds between amino acids.
Grand Prismatic Spring, Yellowstone National Park
Effects of Temperature on Growth
Most of our plates are incubated at 37oC (98.6oF).
• Most grow best between 6.5 and 7.5
• Acidophiles: tolerant to acid
• Able to pump out poisonous H+ fast
enough not to damage the DNA
• Inside the cell stays at 6.5
pH
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Acidic mud pot in Yellowstone Park –
home to the acidophile Sulfolobus acidocaldarius.
Credit: US National Park Service
• Need WATER for growth
• Many bacteria can be
plasmolyzed by high
concentrations of solutes.
Osmotic
Pressure
Osmotic Pressure
• Obligate Halophiles:
require high salt
concentrations
– If placed in fresh water they
will burst and die
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• Facultative Halophiles:
do not require high salt, but
can grow in concentrations
up to 2%
Vibrio parahaemolyticus - halophilic, facultative
rod bacterium that causes a food-borne illness
known as seafood poisoning. Usually
transmitted through eating raw or undercooked
seafood such as oysters. Less commonly, this
organism can cause an infection in the skin when
Chemical Requirements
CARBON: Half the dry weight of a bacterium
NITROGEN: (14%) Protein, Nucleic Acids
SULFUR: Amino acids, vitamins
PHOSPHORUS: Nucleic acids, ATP,
phospholipids
TRACE ELEMENTS: iron, copper, zinc
Used as cofactors
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Aerobes: Microbes that use O2
Obligate aerobes: Require O2
Anaerobes: Do not use O2
Facultative anaerobes: can use O2 when present, but
can still live without
Obligate anaerobes: Unable to use O2, harmed from O2
Aerotolerant anaerobes: cannot use O2 for growth, but
they tolerate it fairly well
Microaerophiles: Aerobic, but only grow in conditions
lower than those in air
• Agar Media: polysaccharide from
a marine algae
– Used as a thickener in foods (jelly)
– Petri dishes, slants, test tubes
Culture
Media
• Nutrient Broth/Agar
– vitamins and other organic growth
factors provided by meat extracts or
yeast extracts
– peptone
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Tryptic Soy Agar (TSA)
• Contains enzymatic digests of casein
and soybean meal
– Provides amino acids and nitrogen
• glucose is the energy source
• Agar used as the gelling agent
Streaking Plates
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Phases of Growth
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