The highly tolerant acetic acid bacterium Gluconacetobacter europaeus adapts to the presence of acetic acid by changes in lipid composition, morphological properties and PQQ-dependent ADH expression.

The strain of acetic acid bacterium, Gluconacetobacter europaeus V3, previously isolated from industrial vinegar-producing bioreactor, tolerates extremely high acetic acid concentrations of up to 10% (v/v). Increased concentration of acetic acid changed the total fatty acid composition of cells by increasing the concentration of a major unsaturated fatty acid, the cis-vaccenic acid. Among the phospholipids, the most significant change was observed for phosphatidylglycerol with 7.3-fold increase and phosphatidylethanolamin with 2.7-fold decrease in the presence of 3% (v/v) of acetic acid. The sizes of cells analyzed with scanning electron microscopy changed from short to long rods in the presence of acetic acid. The cells were covered with spongy layer. The increase of acetic acid concentration from 1 to 2% (v/v) induced the expression of PQQ-dependent alcohol dehydrogenase, but the regulation could not be demonstrated at the transcriptional level. All together, our results suggest that Ga. europaeus activates several adaptive mechanisms to resist the stress of acetic acid.