In order to utilize Saccharomyces cerevisiae strain SCAK-1 collected from deep ocean water (the isolate) in various industrial fields, responses of a function of metabolism to various kinds of stress were investigated. In this study, the decreased weight of culture medium by the activation of glycolytic system in yeast was considered to be a metabolic ability. Four kinds of stress treatment such as temperature, osmosis, alcohol and oxidation were selected. The metabolic ability of the isolate was never decreased by treatments of a high-temperature stress, oxidative stress and high concentration of alcohol stress, although that of the type strain was significantly decreased by these treatments. Furthermore, the metabolic ability of each strain was never influenced by osmotic stress. Finally, maltose utilization ability of the isolate which was considered to be lost in the DOW environment was recovered by the release of glucose repression. The isolate is expected to be used in various industrial fields in the future because it was confirmed that the isolate has resistance to various kinds of stress and was also recovered an important ability of yeast such as the maltose utilization in this study.

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Deep seawater (DSW) contains various resources useful for human life, including cold energy. In this research, we focused on lactic acid bacteria, which are expected to prevent diabetes, hypertension, and obesity. Thirty-two strains of lactic acid bacteria were isolated from Izu-Akazawa DSW. For comparison, 34 strains from surface seawater (SSW) or seaweed from other sources and 25 strains from commercial fermented food (FF) were prepared. All isolates from the three isolation sources (DSW, SSW, FF) were tested for cell growth potential by culture conditions and showed little difference in general characteristics. Next, considering the use of the isolate, the ability of the isolate to ferment soymilk was studied. As a result, there was a difference in the fermentability of soymilk among the isolates from each source. To study the function of soymilk fermented by the isolates, their inhibitory effect against α-glucosidase activity was evaluated. α-Glucosidase activity was well known as a key effector of diabetes, a national disease in Japan today. As a result, there were differences in the inhibitory effect on α-glucosidase activity of soymilk fermented by the isolates. The inhibitory effect of soymilk fermented by isolates from DSW on α-glucosidase activity was shown to be 5.0±0.7 units/mL, which was the strongest among the isolates from three kinds of sources (p＜0.05, SSW; 4.2±1.7 units/mL, FF; 3.3±1.5 units/mL). Then, we performed 16S rDNA analysis of each isolate and identified it as a Lactobacillus species level. As a result, the lactic acid bacteria species isolated from each source had a characteristic, which was the difference in the content of Lactiplantibacillus plantarum. The content of L. plantarum in isolates was independent of soymilk fermentability but associated with inhibitory effect on α-glucosidase activity of fermented soymilk. This study suggested that DSW is a useful source for the isolation of certain lactic acid bacteria, especially L. plantarum. In the future, it is expected that the use of L. plantarum isolated from DSW will expand to the field of human health.

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