Acetic acid bacteria

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]

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

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 product of the 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 common vectors in the propagation of acetic acid bacteria.[2]

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.[3]

Metabolism

Vinegar is produced when acetic acid bacteria act on alcoholic beverages such as wine. They are used to perform specific oxidation reactions through processes called “oxidative fermentations”, that 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.[4]

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.[4]

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,[5] something normally done only by plants.

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References
  1. 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.
  2. Solieri, Laura; Giudici, Paolo (2008-12-16). "Chapter 5". Vinegars of the World. ISBN 978-88-470-0865-6. Retrieved 28 May 2016.
  3. "Sulfur Dioxide: Science behind this anti-microbial, anti-oxidant". Practical Winery & Vineyard Journal. February 2009. p. 4. Retrieved 28 May 2016.
  4. Mamlouk, D. & Gullo, M. Acetic Acid Bacteria: Physiology and Carbon Sources Oxidation. Indian Journal of Microbiology 53, 377–384 (2013).
  5. Kaushal, R.; Walker, T. K. (May 1951). "Formation of cellulose by certain species of Acetobacter". Biochem. J. 48 (5): 618–621. doi:10.1042/bj0480618. PMC 1275385. PMID 14838912.

Further reading
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