Fermented foods have been around long before the aseptic manipulation that is possible in modern research. Many fermented foods are made from plant materials, the surfaces of which are inhabited by a variety of indigenous plant bacteria. For example, it is commonly believed that wine yeast, which is capable of alcoholic fermentation, is present on the skins of grapes, the raw material for wine. Wine yeast migrates into the juice during the pressing process, spontaneously initiating alcoholic fermentation – Is this true? What role did plant indigenous microorganisms play in the origin of wine and other fermented foods?
Our metagenomic analysis of grape skins detected no wine yeast. On the other hand, Aureobasidium pullulans, a plant-associated fungus isolated from grape surfaces, was shown to have the ability to degrade the lipid polymer called cuticular layer that covers the plant surface and to grow on its degradation product, ω-hydroxy fatty acids (Figure 1). Wine yeast does not have this ability and may have difficulty surviving on the surface of grapes. When A. pullulans and wine yeast were co-cultured, they were found to act cooperatively in the alcoholic fermentation of grape berries (Fig. 2). It was found that wine yeast, which is originally difficult to grow on the surface of grapes, initiates alcoholic fermentation with the help of indigenous plant bacteria. This is an interesting finding that is useful for inferring how fermented foods are originated.
Recently, we have newly discovered that koji mold, which is widely used in fermented foods like yeast, grows using ω-hydroxy fatty acids, suggesting that koji mold was originally a plant-derived microorganism. There are old records of koji production in the past, when steamed grains were covered with rice straw and other plant materials to allow koji mold to grow spontaneously. Why don’t you join us in finding out how microorganisms behaved and interacted with each other when fermented foods were originated in the history of mankind?
【Related Papers】
- D. Watanabe, W. Hashimoto*; Adaptation of yeast Saccharomyces cerevisiae to grape-skin environment. Sci. Rep. 13: 9279 (2023)
- H. Sugiura, A. Nagase, S. Oiki, B. Mikami, D. Watanabe, W. Hashimoto*; Bacterial inducible expression of plant cell wall-binding protein YesO through conflict between Glycine max and saprophytic Bacillus subtilis. Sci. Rep. 10: 18691 (2020)