A novel gene having a function of improving acetic acid fermentation in practical level was cloned from a practical acetic acid bacterium belonging to the genus Gluconacetobacter by a method for obtaining a gene having a growth-promoting function in acetic acid-containing medium from the chromosomal DNA library of the acetic acid bacterium. It was made possible to significantly shorten the growth induction period and significantly improve the acetic acid fermentation rate of transformants obtained by introducing the gene into acetic acid bacteria, when such transformants are cultured in the presence of ethanol.