Peroxidases act as a catalyst in reactions utilizing electron donors, for example NADH, to oxidize hydrogen peroxide (H2O2) or other peroxides to water.

Peroxidases

Superoxide Dismutase (SOD) is involved in the reaction that neutralizes the damaging superoxide anions produced during aerobic metabolism. Aerotolerant anaerobes contain only SOD, no catalase. 

Superoxide Dismutase (SOD)

Catalase is an enzyme that converts hydrogen peroxide (H2O2) to water and oxygen

Catalase

All organisms that come in contact with ROS must contain at least one of three essential enzymes to detoxify the reduced oxygen to avoid damage; obligate anaerobes do not contain any of these enzymes:
- Peroxidases
- Superoxide dismutase (SOD)
- Catalase 

Obligate anaerobes cannot grow in the presence of oxygen, which is why they grow densest at the bottom of the Thioglycolate tube. In nature, they can be found in places like deep in the ocean or in anaerobic environments inside of our bodies. 

Obligate Anaerobes

Reactive oxidative species are molecules that contain oxygen that has been partially reduced, typically as a byproduct of aerobic respiration, and therefore contains a highly unstable oxygen ion. ROS are very damaging to structures they come in contact with. Some examples of ROS are peroxides, hydroxyl radical, and hypochlorite ion (household bleach).

Reactive Oxygen Species (ROS)

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

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While many of our tissues in the human body are perfused with oxygenated blood, there are regions where anaerobic conditions exist. Naturally, much of animals intestinal tracts and gut microbiomes are made of obligate anaerobes. Pathologically, necrotic tissue and other circulation issues can create transient anaerobic conditions.

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