The human intestine is inherently inhabited by gut microbiota. Recent studies indicate that the composition of human gut microbiota is associated with various kinds of diseases. Bifidobacteria are one of the predominant beneficial bacteria in the human gut microbiota that have been demonstrated to elicit various beneficial physiological effects in the host. The genus Bifidobacterium is classified into Human-Residential Bifidobacteria (HRB) and non-Human-Residential Bifidobacteria (non-HRB) strains based on their residential habitats. In the present study, we focused on the characteristic features and physiological effects of HRB. We investigated folate production in bifidobacterial strains as the fundamental difference between the HRB and non-HRB strains. We found that the folate production capability of HRB species is generally higher than that of non-HRB species. Furthermore, we studied the molecular mechanisms of the physiological effects of an HRB strain, Bifidobacterium longum subsp. longum BB536, using multi-omics analysis comprising metabolome, metatranscriptome and metagenome analyses. We found that B. longum BB536 alters gut luminal metabolism through interaction with the gut microbial community. These results suggest the potential of HRB to impact host health by modulating the intestinal environment via not only direct production of metabolites but also through crosstalk with the gut microbiota.

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Mental stress is a risk factor not only for mental illness but also for various diseases. Chronic social defeat stress (CSDS) is widely used to develop animal models of depression, which is based on the resident intruder paradigm or inter-male aggression. This review introduces the features of the experimental methods of CSDS and subchronic and mild social defeat stress (sCSDS) and phenotypes of CSDS mice. Our results of omics analyses of cecal metabolites, cecal and fecal microbiota, and ileal gene expression are described with respect to the effects of sCSDS on the murine intestinal ecosystem. Recent approaches to the investigation of food components that alleviate behavioral deficits and physical modulation of CSDS mice are also introduced.

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