Co-cultivation of sake yeast and Kocuria isolates from the sake brewing process

Kocuria isolates collected from the sake brewing process have inhabited the Narimasa Sake Brewery in Toyama, Japan. To investigate the effect of these actinobacterial isolates on the growth and metabolism of sake yeast, co-cultivation of sake yeast and Kocuria isolates was performed in a medium containing tryptone, glucose and yeast extract (TGY), and a solution containing koji (steamed rice covered with Aspergillus oryzae) and glucose. In the TGY medium, the ethanol concentration and the number of living cells of each microorganism were measured. In the koji solution, the concentrations of ethanol and organic acids (citric acid, lactic acid and succinic acid) were measured. The results showed that in TGY media, the growth of each Kocuria isolate in the co-culture of the two Kocuria isolates was similar to that in each monoculture. However, the growth of both Kocuria isolates was inhibited in the co-cultures of sake yeast and Kocuria isolates. On the other hand, the growth and ethanol productivity of sake yeast did not differ between its monoculture and co-cultures with Kocuria isolates. In the koji solution, Kocuria isolates TGY1120_3 and TGY1127_2 affected the concentrations of ethanol and lactic acid, respectively. Thus, Kocuria isolates affected the microbial metabolism, but the effects were not identical between the two isolates. This strongly suggests that bacteria inhabiting a sake brewery may influence the flavor and taste of sake products of the brewery.