MICROBIOLOGICAL ASPECTS OF ACETATE OXIDATION BY ACETIC-ACID BACTERIA,UNFAVORABLE PHENOMENA IN VINEGAR FERMENTATION

Several strains of acetic acid bacteria belonging to the genus Acetoba cter, showing strong acetate oxidation, were screened and their microb iological aspects in acetate oxidation were investigated, When all ava ilable carbon and energy sources were exhausted and only acetic acid r emained in the late stationary phase, the bacteria started to consume the acetic acid that had been accumulated in the culture medium for vi negar fermentation, They grew rapidly, showing the second stationary p hase and a typical biphasic growth curve was observed, The cells from the first growth phase were acid tolerant, while the cells from the se cond growth phase turned over to become acid sensitive, However, no di stinct acetate oxidation took place when oxidizable ethanol and other available carbon sources still remained in the culture medium, Moreove r, no apparent acetate oxidation was observed in vinegar mash in which more than 4.5% of acetic acid was allowed to accumulate, There was a threshold in acetate concentration since the most selected strains oxi dized acetate when the final concentration of acetic acid accumulated was less than 3.7%, When only acetic acid was administrated as the sol e carbon and energy sources, the organisms finally used acetic acid af ter a long lag time, The lag time was shortened by the addition of a s mall amount of readily usable energy source, such as ethanol, From enz ymatic analysis, only acetyl-CoA synthetase increased much among the e nzymes concerning acetyl-CoA formation from acetate, while the enzyme activities of acetate kinase and phosphotransacetylase were not change d significantly, The enzyme activities of isocitrate lyase and malate synthase also increased significantly in the cells when acetate was co nsumed, These results indicate that acetic acid is converted to acetyl -CoA by acetyl-CoA synthetase to put acetate into the TCA cycle as wel l as to the glyoxylate cycle allowing the bacteria to grow rapidly on acetic acid after ethanol exhaustion, Taking together with growth expe riments and enzymatic data accumulated, it was strongly suggested that cells different in physiological characteristics from the first growt h phase emerged in the second growth phase.