Acetic acid bacteria
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| Acetic acid bacteria | |
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| File:Acetobacteraceti.jpg | |
| Acetobacter aceti | |
| Scientific classification | |
| Kingdom: | |
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| Class: | Alphaproteobacteria
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| Order: | |
| Family: | Acetobacteraceae
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| Genera | |
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Acetobacter | |
Acetic acid bacteria (AAB) are a group of gram-negative bacteria which oxidize sugars or ethanol and produce acetic acid during fermentation.[1] The acetic acid bacteria consist of 10 genera in the family Acetobacteraceae.[1] Several species of acetic acid bacteria are used in industry for production of certain foods and chemicals.[1]
Characteristics
All acetic acid bacteria are rod-shaped and obligate aerobes.[1]
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[2] 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 ethanol to carbon dioxide and water using Krebs cycle 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.
One species of Acetobacter, Acetobacter xylinum, is able to synthesize cellulose,[3] 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.
References
- ^ a b c d Raspor P; Goranovic D (2008). "Biotechnological applications of acetic acid bacteria". Critical Reviews in Biotechnology. 28 (2): 101–124. doi:10.1080/07388550802046749. PMID 18568850.
- ^ 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.). Prentice Hall. ISBN 0-13-144329-1.
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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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