Aerotolerance and Bacterial Growth Patterns

aerotolerance

the ability or inability to live in the presence of oxygen

aerobic

with oxygen

anaerobic

without oxygen

aerobic respiration

metabolic pathway that requires the presence of oxygen for the generation of ATP. Oxygen is the final electron acceptor for the electron transport chain

anaerobic respiration

metabolic pathway that generates ATP using molecules other than oxygen as the final electron acceptor for the electron transport chain

fermentation

an alternate metabolic pathway used to generate ATP when there is no electron transport chain, or when the electron transport chain is unavailable

differential media

media that contain specific ingredients to allow one to distinguish selected species or categories of bacteria by visual observation of patterns or appearances

obligate aerobe

requires the presence of atmospheric O2 (20-21%) to survive and grow. O2 is the final electron acceptor for cellular respiration

obligate anaerobe

O2 is toxic to these organisms and they cannot survive prolonged exposure to O2. Obligate anaerobes require a molecule other than O2 as the final electron acceptor for respiration

facultative anaerobe

can grow with or without O2, but grows better when O2 is available for more efficient aerobic respiration. In low O2 environments these microbes can use anaerobic metabolism or fermentation

microaerophilic

requires low concentrations of atmospheric O2 (1-10%) to survive and grow. Higher levels block the activities of their oxidative enzymes and result in death

aerotolerant anaerobe

does not require O2 for growth but can tolerate (survive) exposure to O2. These microbes are not affected by O2 and use fermentation pathways for the generation of ATP

Thioglycollate medium

contains a small amount of agar, thioglycollate that reduces O2 to water, and resazurin, a red O2 indicator

O2 gradient

created in the test tube by the thioglycollate removing O2 from the tube by converting the O2 to water, resulting in an anaerobic environment at the bottom of the tube

reactive oxygen species (ROS)

molecules such as hydrogen peroxide (H2O2) and superoxide radicals (O2-) that microbes in aerobic environments are exposed to

Reactive Oxygen Species (ROS)

Toxic compounds produced during aerobic respiration that must be enzymatically degraded to prevent organism death.

Aerobic Respiration

A process used by obligate aerobes, facultative anaerobes, and microaerophiles that requires oxygen to perform cellular respiration.

H2O2

A type of toxic oxygen radical produced during aerobic respiration.

Catalase

A defense enzyme produced by many aerobic and facultative anaerobic bacteria to detoxify H2O2.

Oxygen Gas (O2(g))

Gas released when the enzyme catalase breaks down H2O2, resulting in the generation of bubbles.

Bubbles Generation

Indicates that oxygen gas is produced, showing the bacterium can produce catalase and degrade toxic H2O2.

No Bubbles

Indicates that oxygen gas is not produced, showing the bacterium does not produce catalase and cannot degrade H2O2.

Terminal Electron Acceptor (TEA)

Oxygen (O2) used by microbes that respire aerobically in the electron transport chain.

Cytochrome c Oxidase

An enzyme produced by some bacteria used in the electron transport chain to distinguish among bacterial groups.

Oxidase Test

An experiment to determine if microbes produce cytochrome c oxidase using BBL DriSlides.

Tetramethyl-p-phenylenediamine (TMPD)

A reagent in DriSlides that produces a color change when oxidation occurs.

Blue Color Change

Indicates that the microbe produces cytochrome c oxidase.

No Color Change

Indicates that the microbe does not produce cytochrome c oxidase.

Mixed Culture

A culture consisting of two or more species of bacteria.

Pure Culture

A culture that contains only a single species of bacteria.

Isolation Technique

Methods used to isolate microbes in a mixed culture.

Quadrant Streak Plate

A method used to test a culture for purity and to separate a mixed culture into discrete cultures.

Bacterial Sample Spread

The process of spreading a bacterial sample over the surface of plates to decrease cell density.

Isolated Colonies

Individual cells that grow from the final quadrant of a quadrant streak plate.