Physiology of Acetobacter and Komagataeibacter spp.: Acetic acid resistance mechanism in acetic acid fermentation

Abstract

Acetic acid bacteria (AAB) are obligate aerobes that belong to the α-Proteobacteria and are used for industrial vinegar production because of their remarkable ability to oxidize ethanol by alcohol dehydrogenase, aldehyde dehydrogenase, and terminal oxidase of respiratory chain members on the cell membrane. Acetic acid tolerance is a crucial ability allowing AAB to stably produce large amounts of acetic acid. Several molecular machineries responsible for acetic acid tolerance in AAB have been reported, including (1) prevention of acetic acid influx into the cell, (2) acetic acid assimilation, (3) acetic acid efflux by transporter or pump, and (4) protection of cytoplasmic proteins against denaturing by general stress proteins. (1) AAB optimize the lipid component proportion of the membrane and by further forming polysaccharide on the surface of the cells to prevent the influx of acetic acid. (2) AAB acquired the ability to convert the intracellular acetic acid in usable energy effectively via the alternative TCA cycle. (3) AAB possess two types of discharging intracellular acetic acid systems, one of which is a putative ABC transporter, and the other is an efflux pump driven by a proton motive force. (4) AAB adapt to the environmental changes in cells by inducing chaperones that stabilize the structure of proteins from acidification of the cell inside, and by synthesizing the enzymes which decompose reactive oxygen species (ROS) to maintain the intracellular environment in good condition. Because acetic acid tolerance in AAB is conferred by several mechanisms, these mechanisms of acetic acid tolerance are reviewed here.