Acetobacter

Acetobacter is a genus of acetic acid bacteria characterized by the ability to convert alcohol (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);
• 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;
• they are used to intentionally acidify beer during long maturation periods in the production of traditional Flemish Sour Ales;
• A. xylinus is the main source of microbial cellulose.

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.

References

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

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