Over the past decade, the gut microbiota has emerged as an essential mediator in the pathophysiology of obesity and related metabolic disorders. In this context, the reciprocal interactions of the gut microbiota structure and their metabolite profiles with host metabolism predisposing to a range of pathological conditions (e.g., insulin resistance) related to energy homeostasis have been increasingly discussed in various animal models and human cohorts. Remarkably, as the role of gut microbial metabolites as critical signaling molecules that function through the complementary host receptors has come to be appreciated, tremendous attention has been focused on the proposed diet-gut microbiota-host homeostasis axis, entailing extensive cross-disciplinary efforts in medical, pharmaceutical, and agricultural sciences. This review will discuss the recent advances in understanding the mechanisms whereby the gut microbiota modulates the effects of diet and shapes the host metabolism either towards or away from obesity and related metabolic conditions. In particular, the interactions of short chain fatty acids (SCFAs), a subset of key gut microbial metabolites, with their specific receptors will be reviewed in relation to host energy homeostatic regulation and evaluated for potential as novel therapeutic targets for diet-induced obesity.

Black currant (Ribes nigrum) has various beneficial properties for human health. In particular, polysaccharide from black currant was found to be an immunostimulating food ingredient and was reported to have antitumor activity in a mouse model. We named it cassis polysaccharide (CAPS). In a previous study, CAPS administration caused tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) production in vitro and in vivo, but the immunological mechanism of CAPS was not demonstrated. In this study, we revealed the CAPS immunostimulating mechanism in vitro. First, we found that CAPS activated dendritic cells (DCs). Second, we investigated whether it depends on Toll-like receptor 4 (TLR4) and myeloid differentiation primary response (Myd). We concluded that CAPS stimulates DCs through Myd88 depending TLR4 signaling and activates Th1-type cytokine release.

Potential fructophilic characteristics of Lactobacillus apinorum, originally isolated from the guts of honeybees (Apis mellifera), were studied in the present study. The species showed typical fructophilic growth characteristics, i.e., active growth on d-fructose, poor growth on d-glucose, and accelerated growth on d-glucose in the presence of electron acceptors. Biochemical characteristics strongly supported classification of the species into fructophilic lactic acid bacteria (FLAB). Furthermore, genetic analyses suggested that the species underwent extensive gene reduction, similar to that recorded for Lactobacillus kunkeei and other FLAB. These data clearly indicated that L. apinorum is the second fructophilic species within the genus Lactobacillus.

Antibiotic resistance genes in the feces of healthy young adult Japanese were analyzed with polymerase chain reaction using specific primers. Antibiotic resistance genes against macrolides (ermB, ermF, ermX, and mefA/E), tetracyclines (tetW, tetQ, tetO, and tetX), β-lactam antibiotics (bla_TEM), and streptomycin (aadE) were detected in more than 50% of subjects. These antibiotic resistance genes are likely widespread in the large intestinal bacteria of young adult Japanese.

Being an autochthonous species in humans, Lactobacillus gasseri is widely used as a probiotic for fermented products. We thoroughly compared the gene contents of 75 L. gasseri genomes and identified two intraspecific groups by the average nucleotide identity (ANI) threshold of 94%. Group I, with 48 strains, possessed 53 group-specific genes including the gassericin T cluster (9 genes) and N-acyl homoserine lactone lactonase. Group II, with 27 strains, including the type strain ATCC 33323, possessed group-specific genes with plasmid- or phage-related annotations. The genomic differences provide evidences for demarcating a new probiotic group within L. gasseri.