GENERAL MICROBIOLOGY - T.P. Pirog - 2004

12. METABOLIC ACTIVITY OF AEROBIC HETEROTROPHS

12.6. INCOMPLETE OXIDATION

12.6.1. Formation of acetic acid and acetic acid bacteria

All acetic acid Bacteria share The ability to produce acids via incomplete oxidation of sugars or alcohols. Acetic acid bacteria are Gram-negative rods with peritrichous (Acetobacter) or polar (Gluconobacter) flagella, showing varying degrees of motility. They are characterized by a high acid tolerance. In their natural habitats, they are typically found on plants. Acetic acid bacteria are divided into peroxydans and suboxydans groups. The peroxydans group comprises organisms that accumulate acid only as an intermediate product, with Gluconobacter oxydans being a typical representative. In organisms of the suboxydans group, acetic acid does not undergo further oxidation (Acetobacter aceti, Acetobacter pasteurianum). Between these two groups, There are many intermediate forms capable of oxidizing acetic acid very slowly. Most acetic acid bacteria require complex nutrient media for growth.

Acetic acid bacteria can grow on media containing ethanol. Ethanol is oxidized by NAD-dependent alcohol and acetaldehyde dehydrogenases to yield acetate and two molecules of NADH. The resulting NADH is used for ATP generation via the Respiratory Chain. In addition to ethanol, acetic acid bacteria oxidize a wide range of other alcohols to their corresponding acids and ketones:

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These organisms lack the ability to synthesize the catabolic Enzymes required for the complete breakdown of these substrates. As a result, acids and alcohols are released into the medium. Acetic acid bacteria are characterized by the presence of PQQ-dependent glucose dehydrogenase.

Of particular interest is the ability of acetic acid bacteria to oxidize D-sorbitol to L-sorbose. Sorbose is required in large quantities for the synthesis of Vitamin C.