Acetic acid bacteria (AAB) are a group of

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

bacteria which

oxidize Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...

s or

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...

and produce

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...

during

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 ...

. The acetic acid bacteria consist of 10

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

in the family

Acetobacteraceae Acetobacteraceae is a family of Gram-negative bacteria, belonging to the order Rhodospirillales, class Alphaproteobacteria. Two distinct clades are recognized. The acetic acid bacteria and a more heterogeneous group including acidophilic and phot ...

. Several species of acetic acid bacteria are used in industry for production of certain foods and chemicals.

Description

All acetic acid bacteria are rod-shaped and

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. Acetic acid bacteria are airborne and are ubiquitous in nature. They are actively present in environments where ethanol is being formed as a product of the fermentation of sugars. They can be isolated from the

nectar Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists ...

of flowers and from damaged fruit. Other good sources are fresh apple

cider Cider ( ) is an alcoholic beverage made from the fermented juice of apples. Cider is widely available in the United Kingdom (particularly in the West Country) and the Republic of Ireland. The UK has the world's highest per capita consumption, ...

and unpasteurized beer that has not been filter sterilized. In these liquids, they grow as a surface film due to their aerobic nature and active motility.

Fruit flies Fruit fly may refer to: Organisms * Drosophilidae, a family of small flies, including: ** ''Drosophila'', the genus of small fruit flies and vinegar flies ** ''Drosophila melanogaster'' or common fruit fly ** ''Drosophila suzukii'' or Asian fruit ...

vinegar eels ''Turbatrix aceti'' (vinegar eels, vinegar nematode, ''Anguillula aceti'') are free-living nematodes that feed on a microbial culture called mother of vinegar (used to create vinegar) and may be found in unfiltered vinegar. They were discovered ...

are considered common vectors in the propagation of acetic acid bacteria. The growth of ''Acetobacter'' in wine can be suppressed through effective sanitation, by complete exclusion of air from wine in storage, and by the use of moderate amounts of

sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...

in the wine as a preservative.

Metabolism

Vinegar Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting simple sugars to et ...

is produced when acetic acid bacteria act on alcoholic beverages such as wine. Specific oxidation reactions occur through oxidative fermentation, which creates vinegar as a byproduct. In the biotechnological industry, these bacteria's oxidation mechanism is exploited to produce a number of compounds such as l-ascorbic acid, dihydroxyacetone, gluconic acid, and cellulose.Mamlouk, D. & Gullo, M. Acetic Acid Bacteria: Physiology and Carbon Sources Oxidation. Indian Journal of Microbiology 53, 377–384 (2013). Besides food industry, some acetic acid bacteria are used as biocatalysts for the industrial production of compounds. They are used as the important biocatalysts for the development of eco-friendly fermentation processes as an alternative to the chemical synthesis. Some genera, such as ''Acetobacter'', can oxidize ethanol to carbon dioxide and water using

Krebs cycle The citric acid cycle (CAC)—also known as the Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and protein ...

enzymes. Other genera, such as ''Gluconobacter'', do not oxidize ethanol, as they do not have a full set of Krebs cycle enzymes. As these bacteria produce acid, they are usually acid-tolerant, growing well below pH 5.0, although the pH optimum for growth is 5.4-6.3. ''

Acetobacter xylinum ''Komagataeibacter xylinus'' is a species of bacteria best known for its ability to produce cellulose, specifically bacterial cellulose. History and taxonomy The species was first described in 1886 by Adrian John Brown, who identified the bacter ...

'' is able to synthesize

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

, something normally done only by plants.

References

External links

International conference on acetic acid bacteria
Rhodospirillales Winemaking Gram-negative bacteria Common names of organisms {{portal bar, Biology

Description

Metabolism

References

Further reading

External links