The only Gram negative bacteria used in the manufacture of fermented foods are the acetic acid-producing rods belonging to the genera Acetobacter, Gluconobacter, and Gluconoace-tobacter (in the Proteobacteria phylum, Family Acetobacteraceae). These bacteria are obligate aerobes, with a respiratory-only metabolism. They make acetic acid via oxidation of ethanol; some species may also have the capacity to further oxidize acetic acid completely to CO2 and water. The acetic acid bacteria are mesophilic, with optimum growth temperatures about 25°C to 30°C.Although acetobacteria are acid-tolerant, their preferred growth pH is generally between 5.3 and 6.3. Some species of Aceto-bacteraceae produce surface film and pigments. Recent changes in the taxonomy of these bacteria has resulted in the transfer of several important species from Acetobacter to Gluconoacetobacter.
It is important to note that other bacteria, including species of Acetobacterium and Clostridium, also make acetic acid as a primary metabolic end-product, but these bacteria are obligate anaerobes and rely on reductive pathways (i.e., reduction of CO2). In wine, beer, cider, and other ethanol-containing products, Acetobacter, Gluconobacter, and Gluconoace-tobacter can act as spoilage organisms. However, they are also the bacteria used in the manufacture of vinegar.
Industrially, vinegar can be produced using either pure culture or natural fermentations. In general, Acetobacter aceti is considered to be the "vinegar bacterium," because it is the most commonly used species in pure culture processes and is also found in natural vinegar fermentations. Other species, however, are also frequently isolated from, or are used in vinegar fermentations, including Acetobacter orleanen-sis, Acetobacter pasteurianus subsp. pasteur-ianus, Gluconoacetobacter europaeus, and Gluconoacetobacter xylinus.
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