In microbiology, it is common practice to isolate and identify microorganisms and characterize them through pure culture. For example, sake yeast, which plays a central role in sake brewing, was isolated and identified from sake mash by Dr. Kikuji Yabe in 1895, and was reported to possess excellent alcohol fermentation ability. While such research methods are obviously extremely important as a basis for microbiology, they also lead to the withdrawal of microorganisms from their natural, complex growing environment. The true way of life of microorganisms in the presence of various components and environmental factors, and undergoing dynamic changes over time, as in the production of fermented foods, tends to be overlooked by conventional research methods.
The more we learn about the diversity and depth of fermented foods throughout the world, the more we are amazed. However, at the same time, we can find the commonality when focusing on the transition of microflora in the production process of fermented foods. In the traditional manufacturing processes of sake, soy sauce, miso, black vinegar, pickles, and bread, the raw materials are first fermented by lactic acid bacteria, and then, subjected to alcoholic fermentation by yeast that appears out of nowhere. Such commonality may suggest a principle governing food fermentation. In our laboratory, we have conducted research focusing on the interaction between yeast and lactic acid bacteria in the traditional sake brewing process known as “kimoto” (Fig. 1). As a result, we discovered a novel phenomenon in which lactic acid bacteria inhibit yeast’s alcohol fermentation (Fig. 2). Since ethanol produced is highly toxic to other microorganisms, the suppression of alcoholic fermentation may be essential for different microorganisms to live together in the same environment. We will continue to create new values for fermented foods by focusing on the symbiotic interaction between microorganisms in the traditional production process of fermented foods and clarifying its significance.
【Related Papers】
- D. Watanabe*, M. Kumano, Y. Sugimoto, H. Takagi; Spontaneous attenuation of alcoholic fermentation via the Cyc8p-Tup1p complex of Saccharomyces cerevisiae. (submitted)
- D. Watanabe, H. Takagi*; Yeast prion-based metabolic reprogramming induced by bacteria in fermented foods. FEMS Yeast Res. 19: foz061 (2019)
- D. Watanabe*, M. Kumano, Y. Sugimoto, M. Ito, M. Ohashi, K. Sunada, T. Takahashi, T. Yamada, H. Takagi; Metabolic switching of sake yeast by kimoto lactic acid bacteria through the [GAR+] non-genetic element. J. Biosci. Bioeng.126: 624-629 (2018)