Role of intracellular esterases in the production of esters by Acetobacter pasteurianus

Esters are the major flavor compounds produced by Acetobacter sp. during vinegar production. The two genes encoding the esterases in the bacteria were disrupted, and the effects of the disruptions studied. When cultured in the presence of ethanol, the est1 gene-disrupted mutant (DE1K) did not produce any ethyl acetate or isoamyl acetate. However, the disruption of est2 did not affect the ester production. Ethyl acetate production by N-23 (pME122P) and DE1K (pME122P), which contain est1, was 1.7-fold higher than that by the wild type, N-23. On analyzing the relationship between ethyl acetate production and the extracellular ethanol and acetic acid concentrations, we found that the highest amount of ethyl acetate was produced when the molar ratio of ethanol and acetic acid was 1:1. These results indicate that the ester production by Acetobacter sp. is mostly catalyzed by the intracellular esterase, esterase-1, with ethanol and acetic acid used as the substrates.