Acetic acid bacteria

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Acetic acid bacteria
Acetobacteraceti.jpg
Acetobacter aceti
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Alphaproteobacteria
Order: Rhodospirillales
Family: Acetobacteraceae
Genera

Acetobacter
Acidicaldus
Acidiphilium
Acidisphaera
Acidocella
Acidomonas
Asaia
Belnapia
Craurococcus
Gluconacetobacter
Gluconobacter
Granulibacter
Kozakia
Leahibacter
Muricoccus
Neoasaia
Oleomonas
Paracraurococcus
Rhodopila
Roseococcus
Rubritepida
Saccharibacter
Stella
Swaminathania
Teichococcus
Zavarzinia

Not to be confused with Acetobacterium, a distinct group of organisms.

Acetic acid bacteria (AAB) derive their energy from the oxidation of ethanol to acetic acid during fermentation. They are gram-negative, aerobic, rod-shaped bacteria.

Occurrence[edit]

Acetic acid bacteria are airborne and are ubiquitous in nature. They are actively present in environments where ethanol is being formed as a result of fermentation of sugars. They can be isolated from the nectar of flowers and from damaged fruit. Other good sources are fresh apple cider 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 as a common vector in propagating acetic acid bacteria[1] in nature.

Suppression[edit]

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 in the wine as a preservative.

Metabolism[edit]

Vinegar is produced when acetic acid bacteria act on alcoholic beverages such as wine.

Some genera, such as Acetobacter, can oxidize acetic acid to carbon dioxide and water using Krebs cycle enzymes. Other genera, such as Gluconobacter, do not further oxidize acetic acid, 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.

One species of Acetobacter, Acetobacter xylinum, is able to synthesize cellulose,[2] something normally done only by plants.

Genus Acetobacter[edit]

Acetobacter is a genus of acetic acid bacteria characterized by the ability to convert ethanol to acetic acid in the presence of oxygen. Several species are in this genus, and other bacteria are capable of forming acetic acid under various conditions, but all of the Acetobacter species are known by this characteristic ability.

Acetobacter is of particular importance commercially, because some species are used in the production of vinegar (intentionally converting the ethanol in wine to acetic acid), and they can destroy wine which they infect by producing excessive amounts of acetic acid or ethyl acetate, both of which can render the wine unpalatable. Acetobacter species are also used to intentionally acidify beer during long maturation periods in the production of traditional Flemish sour ales.

Acetobacter species can be easily distinguished in the laboratory by the growth of colonies on a medium containing about 7% ethanol and enough calcium carbonate to render it partially opaque. When Acetobacter colonies form enough acetic acid from the ethanol, the calcium carbonate around the colonies dissolves, forming a very distinct clear zone.

References[edit]

  • Madigan M; Martinko J (editors). (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0-13-144329-1. 

Further reading[edit]

External links[edit]