Acetic acid bacteria
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|Acetic acid bacteria|
Acetic acid bacteria (AAB) are bacteria that derive their energy from the oxidation of ethanol to acetic acid during fermentation. They are Gram-negative, aerobic, rod-shaped bacteria. They are not to be confused with the genus Acetobacterium, which are anaerobic homoacetogenic facultative autotrophs and can reduce carbon dioxide to produce acetic acid, for example, Acetobacterium woodii.
The acetic acid bacteria are usually airborne and are ubiquitous in nature. They are actively present in environment 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. Vinegar is produced when acetic acid bacteria act on alcoholic beverages such as wine. Fruit flies or Vinegar eels are considered as a common vector in propagating acetic acid bacteria in nature.
Some genera, such as Acetobacter, can eventually 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.
Acetobacter is a genus of acetic acid bacteria characterized by the ability to convert ethanol to acetic acid in the presence of oxygen. There are several species within this genus, and there are other bacteria capable of forming acetic acid under various conditions; but all of the Acetobacter are known by this characteristic ability.
Acetobacter are of particular importance commercially, because they are used in the production of vinegar (intentionally converting the ethanol in the 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 are also used to intentionally acidify beer during long maturation periods in the production of traditional Flemish Sour Ales.
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. Acetobacter can be easily distinguished in the laboratory by their growth of colonies on a medium containing about 7% ethanol, and enough calcium carbonate to render the medium 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.
- Acetobacterium, a new genus of hydrogen-oxidizing, carbon dioxide-reducing, anaerobic bacteria 1977, Int J Syst Bacteriol 27, 355-361.
- Vinegars of the World. Chapter 5. ISBN 978-88-470-0865-6
- Formation of cellulose by certain species of Acetobacter Biochem J. 1951 May; 48(5): 618–621
- Madigan M; Martinko J (editors). (2005). Brock Biology of Microorganisms (11th ed. ed.). Prentice Hall. ISBN 0-13-144329-1.
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
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