Hot springs are unique natural environments that have been used for recreational and/or therapeutic purposes (balneotherapy) since ancient times in various countries, especially, Japan. Japanese hot spring therapy, called "touji", is world-renowned. Multilateral and comprehensive scientific study of hot springs and their benefits could contribute to making Japan a tourism-oriented country. As a first step, microbes living in hot springs and their genes were analyzed to understand the hot spring mircobiome. We detected 27 novel microorganisms and type-specific tRNA degradation. Hot spring water (HSW) consumption is one of the methods of balneotherapy. It has been reported that consumption of hydrogen carbonate- or sulfur-containing water may be prevent and/or improve type 2 diabetes. However, since the molecular mechanisms underlying the effects of balneotherapy have not been well elucidated, the physiological effects of HSW consumption were evaluated using omics-based approaches. In the HSW consumption periods, serum glycoalbumin levels, a glycemic control index, were significantly decreased. Metabolome analysis showed that concentrations of 19 blood metabolites including 4 glycolysis-related metabolites and 3 amino acids were significantly changed in the HSW consumption periods as compared with the tap water consumption periods, suggesting that HSW consumption may induce glycolysis and proteolysis alteration. Additionally, 8 families of gut microbiota were significantly changed, out of which lean-associated bacteria was significantly increased. Moreover, experiment on murine models was also conducted and these models may be useful for screening to evaluate the effectiveness of HSW consumption. The current research provides beneficial information for future studies investigating the molecular basis of balneotherapy. Taken together, our findings provide new insights into the microbial ecosystems in hot springs and the molecular mechanisms underlying the effects of balneotherapy. These findings contribute to the understanding of hot springs and their effect in improving human health.
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