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