Since the above results indicated that disruption of the FIS1 gene results in inhibition of mitochondrial fragmentation during sake brewing, we next investigated the effect of inhibiting mitochondrial fragmentation during sake brewing on the metabolism of constituents during sake brewing by disrupting the FIS1 gene. Organic acids are important constituents of sake, and several studies suggest the partial involvement of mitochondria in the formation of organic acids during sake brewing ( 11 and 12). Therefore, we analyzed the effect of the disruption of the FIS1 gene on the formation of organic acids during sake brewing. Sake was brewed with WT and fis1Δ strains of a laboratory strain, BY4743, for 22 d, and the contents of organic acids were analyzed and compared. Sake brewing proceeded without significant deviation, as revealed by the amount of carbon dioxide evolved ( Fig. 2A) with normal final ethanol concentrations (WT: 15.6%, fis1Δ: 16.3%). The analysis showed that the content of malate, an important organic acid, increased in fis1Δ (102.0±5.2 mg/l) to a greater extent than that in WT (71.8±4.9 mg/l) ( Fig. 2B). However, perhaps owing to the genetic background of the laboratory strain, the malate content was much lower than those of other organic acids, which is not consistent with results obtained for industrial sake yeast strains ( 11, 12 and 13). To the contrary, the content of fumarate in sake brewed with the laboratory strains was higher than that brewed with industrial strains reported previously ( 11, 12 and 13), suggesting that the metabolism of malate and fumarate is different between the industrial and laboratory strains.