chapter 6: microbial growth. requirements for growth physical requirements –temperature –ph...
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Chapter 6: Microbial Growth
Requirements for Growth
• Physical Requirements– Temperature– pH– Osmotic Pressure
• Chemical Requirements– Carbon– Nitrogen,Sulfur, Phosphorus– Oxygen
Temperature
• 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°
• Mesophiles: moderate-temp-loving– Optimal 25-40°– Most common microbes, spoilage and
disease
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Artic Sea bacteria:Strain34h, stained fluorescentblue for better viewing.
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TemperatureThermophiles: heat-loving
– Optimal 50-60° – Important in compost piles
Hyperthermals: extreme thermophiles– Optimal 80°+– Hot springs, volcanoes
How do they tolerate the high temperatures?
• special enzymes fold their DNA into special heat-stable coils
• enzymes themselves are heat stable with extra bonds between amino acids.
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SEM of a thermophilic Bacillus species isolated from a compost pile at 55°
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Grand Prismatic Spring, Yellowstone National Park
Effects of Temperature on Growth
Most of our plates are incubated at 32-35oC
pH• 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
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Acidic mud pot in Yellowstone Park – home to the acidophile Sulfolobus acidocaldarius. Credit: US National Park Service
Osmotic Pressure
• Need WATER for growth• Many bacteria can be
plasmolyzed by high concentrations of solutes.
Osmotic Pressure
• Obligate Halophiles: require high salt concentrations– If placed in fresh water
they will burst and die
• Facultative Halophiles: do not require high salt, but can grow in concentrations up to 2%
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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
an open wound is exposed to warm seawater.
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
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
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Culture Media
• Agar Media: polysaccharide from a marine algae– Used as a thickener in foods (jelly)– Petri dishes, slants, test tubes
• 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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http://www.sumanasinc.com/webcontent/animations/content/streakplate.html
Phases of Growth