Acetic acid bacteria (AAB) are a group of

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

bacteria which

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

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 Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...

s or

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

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 compone ...

during

fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...

. The acetic acid bacteria consist of 10

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

in the family

Acetobacteraceae Acetobacteraceae is a Family (biology), 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 ac ...

. 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 ...

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 viscous, sugar-rich liquid produced by Plant, plants in glands called nectaries, either within the flowers with which it attracts pollination, pollinating animals, or by extrafloral nectaries, which provide a nutrient source to an ...

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

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

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 or vinegar eels 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 colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...

in the wine as a preservative.

Metabolism

Vinegar Vinegar () is an aqueous solution of diluted acetic acid and trace compounds that may include flavorings. Vinegar typically contains from 5% to 18% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting ...

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—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of biochemical reactions that release the energy stored in nutrients through acetyl-CoA oxidation. The e ...

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 bac ...

'' is able to synthesize

cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...

, 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