Aerotolerant anaerobes use

fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...

to produce ATP. They do not use

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

, but they can protect themselves from reactive oxygen molecules. In contrast,

obligate anaerobe Obligate anaerobes are microorganisms killed by normal atmospheric concentrations of oxygen (20.95% O2). Oxygen tolerance varies between species, with some species capable of surviving in up to 8% oxygen, while others lose viability in environm ...

s can be harmed by reactive oxygen molecules. There are three categories of anaerobes. Where

obligate aerobe An obligate aerobe is an organism that requires oxygen to grow. Through cellular respiration, these organisms use oxygen to metabolise substances, like sugars or fats, to obtain energy. In this type of respiration, oxygen serves as the terminal e ...

s require oxygen to grow,

s are damaged by oxygen, aerotolerant organisms cannot use oxygen but tolerate its presence, and

facultative anaerobe A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...

s use oxygen if it is present but can grow without it. Most aerotolerant anaerobes have

superoxide dismutase Superoxide dismutase (SOD, ) is an enzyme that alternately catalyzes the dismutation (or partitioning) of the superoxide () radical into ordinary molecular oxygen (O2) and hydrogen peroxide (). Superoxide is produced as a by-product of oxygen me ...

and (non-catalase)

peroxidase Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x are a large group of enzymes which play a role in various biological processes. They are named after the fact that they commonly break up peroxides. Functionality Peroxidases typically ca ...

but don't have

catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting t ...

. More specifically, they may use a

NADH oxidase Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an aden ...

NADH peroxidase In enzymology, a NADH peroxidase () is an enzyme that catalyzes the chemical reaction :NADH + H+ + H2O2 \rightleftharpoons NAD+ + 2 H2O The presumed function of NADH peroxidase is to inactivate H2O2 generated within the cell, for example by gl ...

(NOX/NPR) system or a

glutathione peroxidase Glutathione peroxidase (GPx) () is the general name of an enzyme family with peroxidase activity whose main biological role is to protect the organism from oxidative damage. The biochemical function of glutathione peroxidase is to reduce lipid h ...

system. An example of an aerotolerant anaerobe is ''

Cutibacterium acnes ''Cutibacterium acnes'' (formerly ''Propionibacterium acnes'') is the relatively slow-growing, typically aerotolerant Anaerobic organism, anaerobic, gram-positive bacterium (rod) linked to the skin condition of acne vulgaris, acne; it can also ca ...

''.

References

Microbiology {{microbiology-stub