Evidence for ethanol-dependent acetic acid resistance in <i>Acetobacter pasteurianus</i> strain SKU1108

Vinegar is produced by acetic acid fermentation by acetic acid bacteria such as <i>Komagataeibacter</i> spp. and <i>Acetobacter</i> spp. Resistance to acetic acid is an important feature of these microorganisms. At least two mechanisms have been proposed for acetic acid resistance: acetate metabolism and acetic acid efflux. The gene <i>aarC</i> is crucial in the acetate metabolism of <i>Acetobacter</i> sp. Here, a mutant derivative of <i>Acetobacter pasteurianus</i> strain SKU1108, devoid of <i>aarC,</i> failed to grow on acetate. In the absence of ethanol, the mutant was sensitive to acetic acid. However, in the presence of ethanol, it was resistant to acetic acid. These observations suggest a novel mechanism of AarC-independent but ethanol-dependent acetic acid resistance of <i>A. pasteurianus</i>. We can now find acetic acid-resistant mechanisms independent of acetate metabolism in growing cell-based experiments, which may promote elucidation of mechanism(s) of acetic acid resistance that involve as-yet-unidentified molecules.