Acetic acid bacteria

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Acetobacter aceti
Scientific classification
Kingdom:	Bacteria
Phylum:	Proteobacteria
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

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 in nature.

Suppression

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

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, something normally done only by plants.

Genus Acetobacter

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.

Further reading

• Ecological occurrence of Gluconacetobacter diazotrophicus and nitrogen-fixing Acetobacteraceae members: their possible role in plant growth promotion 2008. Microb Ecol. 55(1):130-40.
• Genera and species in acetic acid bacteria, 2008 Int. J. Food Microbiol. Volume 125, Issue 1, Pages 15–24.
• Polyphasic taxonomy of acetic acid bacteria: An overview of the currently applied methodology, 2008 Int. J. Food Microbiol. Volume 125, Issue 1, Pages 2–14
• Biotechnological applications of acetic acid bacteria, 2008, Critical Reviews in Biotechnology, Volume 28, Issue 2, 101-124
• Evaluation of viability and growth of Acetobacter senegalensis under different stress conditions, 2013 Int. J. Food Microbiol.Volume 163,issue 2-3, 204-213

External links

• International conference on acetic acid bacteria