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, aerobic, rod-shaped bacteria.
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 they do not have a full set of Krebs cycle enzymes.
Some acetic acid bacteria, notably ''Acetobacter xylinum'', are known to synthesize cellulose, something normally only done by plants.
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.