Acetic acid bacteria

Acetic acid bacteria are bacteria that derive their energy from the oxidation of ethanol to acetic acid during respiration. They are Gram-negative rod-shaped bacteria that require oxygen.

The acetic acid bacteria are found in nature where ethanol is being formed as a result of yeast fermentation of sugars and plant carbohydrates. They can be isolated from the nectar of flowers and from damaged fruit. Other good sources are fresh apple cider and unpasteurized beer which has not been filter sterilized. In these liquids the acetic acid bacteria 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.

Some genera, such as Acetobacter, can eventually oxidize acetic acid to carbon dioxide and water using Krebs cycle enzymes. Other genera, such as Gluconobacter, doesn't further oxidize acetic acid, as it does not have a full set of Krebs cycle enzymes.

As these bacteria produce acid, they are unusually acid tolerant, growing well below pH 5.0, although the pH optimum for growth is 5.4-6.3.