The Genomes of acetic acid bacteria

Abstract

Acetic acid bacteria are strictly aerobic, acidophilic organisms that are known for their rapid incomplete oxidation of alcohols, polyols, or sugars and their derivatives. They are the elicitors of various wine faults, mainly the formation of vinegar taste due to direct oxidation of ethanol to acetic acid with acetaldehyde as an intermediate when oxygen is available. Complete genome sequences provided rich information on the physiology and biochemistry of acetic acid bacteria and reflected their adaptation to nutrient-rich habitats. The stereo- and regioselective direct oxidations are performed by membrane-bound pyrroloquinoline quinone (PQQ) or flavine-dependent dehydrogenases with their active sites facing toward the periplasm. The membrane-bound dehydrogenases feed the electrons derived from the oxidations directly into a short electron transport chain, conserving energy by forming a proton motive force. Besides the membrane-bound dehydrogenases, the organisms have an additional set of dehydrogenases located in the cytoplasm. They may function mainly in carbon assimilation. The central metabolism seems to be specialized in providing building blocks for biosynthesis. Glycolysis is incomplete due to a missing phosphofructokinase, but a pentose phosphate cycle is functional. In the genus Gluconobacter, the tricarboxylic acid (TCA) cycle is not closed, because succinate thiokinase and succinate dehydrogenase are missing. Also, there is no glyoxylic acid cycle and gluconeogenetic phosphoenolpyruvate formation from acetate. Therefore, it is not possible to overoxidize acetate. Organisms like Acetobacter have a complete TCA and a glyoxylic acid cycle, allowing them to overoxidize acetate in a second growth phase. For the activation of acetate in some strains, a succinyl-coenzyme A (CoA):acetate CoA-transferase (AarC) is present, which replaces succinyl-CoA synthetase in the TCA.