Correlation between ethanol resistance and characteristics of PQQ-dependent ADH in acetic acid bacteria

The aim of this study was to understand the correlation between ethanol resistance and characteristics of PQQ-dependent ADH in acetic acid bacteria. Two ethanol-tolerant strains, FY-24 and DY-5, identified as Acetobacter pasteurianus were isolated from Chinese vinegar Pei . FY-24 and DY-5 maintained the growth and fermentation ability with 12 % (v/v) ethanol at 37 °C, but A. pasteurianus AS1.41 (widely used in China) could only be resistant to 10 % ethanol. ADH activities of FY-24 (6.13 U/mg) and DY-5 (5.41 U/mg) were much higher than that of AS1.41 (1.57 U/mg) at 8 % ethanol. Using purified ADH, it was shown that the ADHs from FY-24 and DY-5 exhibited a higher ethanol tolerance as ethanol increasing from 10 to 40 %. The optimum ethanol concentration for ADHs of FY-24 and DY-5 was 10 %, but was 5 % for that of AS1.41. Additionally, ADHs from FY-24 and DY-5 exhibited a higher resistance to temperature and acetic acid than that of AS1.41. From the amino acid sequence of ADH subunits, a certain amount of residues were found in the ADHs of FY-24 and DY-5 (411th D and 731th N in subunit I, 170th D in subunit II and 40th G in subunit III), which were different from that of AS1.41. The difference in amino acid residues might partly relate to the ethanol tolerance. Our results suggested that FY-24 and DY-5 could be developed for high ethanol acetic acid fermentation.