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# 6.10.4: Oxygen

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Oxygen requirements vary among microorganisms.

## LEARNING OBJECTIVES

Identify the role of oxygen in microbial growth

## Key Points

• An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment.
• An anaerobic organism or anaerobe is any organism that does not require oxygen for growth.
• Normal microbial culturing occurs in an aerobic environment which poses a problem when culturing anaerobes; requiring one of a number of techniques to be used to keep oxygen out of the culturing setup.

## Key Terms

• anaerobic: Without oxygen; especially of an environment or organism.
• aerobic respiration: metabolic reactions and processes that take place in the cells of organisms and require oxygen to convert biochemical energy from nutrients into adenosine triphosphate (ATP)
• aerobic: Living or occurring only in the presence of oxygen.
• aerotolerant anaerobe: an organism that does not require oxygen to sustain its metabolic processes, but is able to survive in the presence of oxygen

An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. Several varietis of aerobes exist. Obligate aerobes require oxygen for aerobic cellular respiration. In a process known as cellular respiration, these organisms use oxygen to oxidize substrates (for example sugars and fats) in order to obtain energy. Facultative anaerobes can use oxygen, but also have anaerobic (i.e. not requiring oxygen) methods of energy production. Microaerophiles are organisms that may use oxygen, but only at low concentrations. Aerotolerant organisms can survive in the presence of oxygen, but they are anaerobic because they do not use it as a terminal electron acceptor.

An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present. For practical purposes there are three categories: obligate anaerobes, which cannot use oxygen for growth and are even harmed by it. Aerotolerant organisms, which cannot use oxygen for growth, but tolerate the presence of it. And finally, facultative anaerobes, which can grow without oxygen but can utilize oxygen if it is present.

Since normal microbial culturing occurs in atmospheric air, which is an aerobic environment, the culturing of anaerobes poses a problem. Therefore, a number of techniques are employed by microbiologists when culturing anaerobic organisms, for example, handling the bacteria in a glovebox filled with nitrogen or the use of other specially-sealed containers.

The GasPak System is an isolated container that achieves an anaerobic environment by the reaction of water with sodium borohydride and sodium bicarbonate tablets to produce hydrogen gas and carbon dioxide. Hydrogen then reacts with oxygen gas on a palladium catalyst to produce more water, thereby removing oxygen gas.

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