Human gut-associated Bifidobacterium species salvage exogenous indole, a uremic toxin precursor, to synthesize indole-3-lactic acid via tryptophan.

Indole in the gut is formed from dietary tryptophan by a bacterial tryptophan-indole lyase. Indole not only triggers biofilm formation and antibiotic resistance in gut microbes but also contributes to the progression of kidney dysfunction after absorption by the intestine and sulfation in the liver. As tryptophan is an essential amino acid for humans, these events seem inevitable. Despite this, we show in a proof-of-concept study that exogenous indole can be converted to an immunomodulatory tryptophan metabolite, indole-3-lactic acid (ILA), by a previously unknown microbial metabolic pathway that involves tryptophan synthase ß subunit and aromatic lactate dehydrogenase. Selected bifidobacterial strains converted exogenous indole to ILA via tryptophan (Trp), which was demonstrated by incubating the bacterial cells in the presence of (2-13C)-labeled indole and l-serine. Disruption of the responsible genes variedly affected the efficiency of indole bioconversion to Trp and ILA, depending on the strains. Database searches against 11,943 bacterial genomes representing 960 human-associated species revealed that the co-occurrence of tryptophan synthase ß subunit and aromatic lactate dehydrogenase is a specific feature of human gut-associated Bifidobacterium species, thus unveiling a new facet of bifidobacteria as probiotics. Indole, which has been assumed to be an end-product of tryptophan metabolism, may thus act as a precursor for the synthesis of a host-interacting metabolite with possible beneficial activities in the complex gut microbial ecosystem.

An Exploratory Study on Seasonal Variation in the Gut Microbiota of Athletes: Insights from Japanese Handball Players.

Despite accumulating evidence that suggests a unique gut microbiota composition in athletes, a comprehensive understanding of this phenomenon is lacking. Furthermore, seasonal variation in the gut microbiota of athletes, particularly during the off-season, remains underexplored. This study aimed to compare the gut microbiotas between athletic subjects (AS) and non-athletic subjects (NS), and to investigate variations between athletic and off-season periods. The data were derived from an observational study involving Japanese male handball players. The results revealed a distinct gut microbiota composition in AS compared with NS, characterized by significantly higher alpha-diversity and a greater relative abundance of Faecalibacterium and Streptococcus. Moreover, a comparative analysis between athletic and off-season periods in AS demonstrated a significant change in alpha-diversity. Notably, AS exhibited significantly higher alpha-diversity than NS during the athletic season, but no significant difference was observed during the off-season. This study demonstrates the characteristics of the gut microbiota of Japanese handball players and highlights the potential for changes in alpha-diversity during the off-season. These findings contribute to our understanding of the dynamic nature of the gut microbiota of athletes throughout the season.

Enriched metabolites that potentially promote age-associated diseases in subjects with an elderly-type gut microbiota.

We previously investigated the gut microbiota of 453 healthy Japanese subjects aged 0 to 104 years and found that the composition of the gut microbiota could be classified into some age-related clusters. In this study, we compared fecal metabolites between age-matched and age-mismatched elderly subjects to examine the roles of the gut microbiota in the health of the elderly. Fecal metabolites in 16 elderly subjects who fell into an age-matched cluster (elderly-type gut microbiota group, E-GM) and another 16 elderly subjects who fell into an age-mismatched cluster (adult-type gut microbiota group, A-GM) were measured by CE-TOF-MS. A total of eight metabolites were significantly different between the groups: cholic acid and taurocholic acid were enriched in the A-GM group, whereas choline, trimethylamine (TMA), N8-acetylspermidine, propionic acid, 2-hydroxy-4-methylvaleric acid, and 5-methylcytosine were enriched in the E-GM group. Some metabolites (choline, TMA, N8-acetylspermidine) elevated in the E-GM group were metabolites or precursors reported as risk factors for age-associated diseases such as arteriosclerosis and colorectal cancer. The abundance of some species belongs to Proteobacteria, which were known as TMA-producing bacteria, was increased in the E-GM group and correlated with fecal TMA levels. In vitro assays showed that these elderly-type fecal metabolites suppressed the expression of genes related to tight junctions in normal colonic epithelial cells and induced the expression of inflammatory cytokines in colon cancer cells. These findings suggest that metabolites produced by the aged gut microbiota could contribute to intestinal and systemic homeostasis and could be targeted for preventing aging-associated diseases.

Genome-wide association studies and heritability analysis reveal the involvement of host genetics in the Japanese gut microbiota.

Numerous host extrinsic and intrinsic factors affect the gut microbiota composition, but their cumulative effects do not sufficiently explain the variation in the microbiota, suggesting contributions of missing factors. The Japanese population possesses homogeneous genetic features suitable for genome-wide association study (GWAS). Here, we performed GWASs for human gut microbiota using 1068 healthy Japanese adults. To precisely evaluate genetic effects, we corrected for the impacts of numerous host extrinsic and demographic factors by introducing them as covariates, enabling us to discover five loci significantly associated with microbiome diversity measures: HS3ST4, C2CD2, 2p16.1, 10p15.1, and 18q12.2. Nevertheless, these five variants explain only a small fraction of the variation in the gut microbiota. We subsequently investigated the heritability of each of the 21 core genera and found that the abundances of six genera are heritable. We propose that the gut microbiota composition is affected by a highly polygenic architecture rather than several strongly associated variants in the Japanese population.

Author Correction: Impact of a bathing tradition on shared gut microbes among Japanese families.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Neonatal oral fluid as a transmission route for bifidobacteria to the infant gut immediately after birth.

Bifidobacteria are one of the most abundant bacterial groups in the infant gut microbiota and are closely associated with infant health and can potentially affect health in later life. However, the details regarding the source of bifidobacteria have yet to be completely elucidated. This study aimed to assess neonatal oral fluid (OF) as a transmission route for bifidobacteria to the infant gut during delivery. Neonatal OF and infant feces (IF) were collected immediately and one month after birth from 15 healthy vaginally delivered newborns. Bifidobacterium strains were isolated from OF and IF samples, and the similarity of strains between the OF-IF pairs was evaluated based on the average nucleotide identity (ANI) value. The 16S rRNA gene sequencing results revealed the presence of Bifidobacteriaceae at >1% relative abundance in all OF samples. Bifidobacterium strains were isolated from OF (9/15) and IF (11/15) samples, and those sharing high genomic homology (ANI values >99.5%) between the neonatal OF and IF samples were present in one-third of the OF-IF pairs. The results of this study indicate that viable bifidobacteria are present in neonatal OF and that OF at birth is a possible transmission route of bifidobacteria to the infant gut.

Heat-killed Lactobacillus helveticus strain MCC1848 confers resilience to anxiety or depression-like symptoms caused by subchronic social defeat stress in mice.

The gut microbiota is involved in the pathogenesis of stress-related disorders. Probiotics can benefit the central nervous system via the microbiota-gut-brain axis, which raises the possibility that probiotics are effective in managing depression. In the present study, we examined the effects of heat-killed Lactobacillus helveticus strain MCC1848 in subchronic and mild social defeat stress (sCSDS) model mice (a widely used animal model of depression). MCC1848 supplementation significantly enhanced the interaction time in the social interaction test and sucrose preference ratio in the sucrose preference test, suggesting that MCC1848 improved anxiety- or depressive-like behaviors in sCSDS mice. The gene expression profile analysis of the nucleus accumbens, which plays an important role in stress resilience, indicated that MCC1848 ameliorated sCSDS-induced gene expression alterations in signal transduction or nervous system development. These findings suggest that MCC1848 supplementation is useful as a preventive strategy for chronic-stress-induced depression.

Impact of a bathing tradition on shared gut microbe among Japanese families.

Sharing of Bifidobacterium longum strains had recently been shown to occur among Japanese family members, a phenomenon that is not confined to mother-infant pairs. In the current study, we investigated if bathtub water is a possible vehicle for the exchange of strains as a consequence of a Japanese custom to share bathtub water by family members during bathing practices. A total of twenty-one subjects from five Japanese families, each consisting of parents with either 2 or 3 children, were enrolled in this study and the fecal microbiota of all participants was determined. Viable bifidobacterial strains were isolated from all bathtub water samples. A subsequent comparative genome analysis using ninety-eight strains indicated that certain strain-sets, which were isolated from feces and bathtub water, share near identical genome sequences, including CRISPR/Cas protospacers. By means of unweighted UniFrac distance analysis based on 16S rRNA gene analysis of 59 subjects from sixteen Japanese families, we showed that the fecal microbiota composition among family members that share bathtub water is significantly closer than that between family members that do not engage in this practice. Our results indicate that bathtub water represents a vehicle for the transmission of gut bacteria, and that the Japanese custom of sharing bathtub water contributes to the exchange of gut microbes, in particular bifidobacteria, among family members.

The Combination of Bifidobacterium breve and Three Prebiotic Oligosaccharides Modifies Gut Immune and Endocrine Functions in Neonatal Mice.

BACKGROUND: Several types of oligosaccharides are used in infant formula to improve the gut microbiota of formula-fed infants. We previously reported that a combination of 3 oligosaccharides (lactulose, raffinose, and galacto-oligosaccharides; LRG) and Bifidobacterium breve effectively increased B. breve numbers, acetate, and the expression of several immune- and gut hormone-related mRNAs in neonatal mice gut. OBJECTIVE: We investigated whether changes in neonatal gut microbiota alter gut immune and endocrine development. METHODS: We first compared postnatal day (PD) 14 with PD21 in C57BL/6J male mouse pups to identify the physiologic immune and endocrine changes during development. In a separate study, we administered phosphate-buffered saline (control group; CON), B. breve M-16V (M-16V), or M-16V + LRG to male mouse pups from PD6 to PD13, and analyzed the gut microbiota and immune and endocrine parameters on PD14 to evaluate whether M-16V + LRG accelerates gut immune and endocrine development. RESULTS: The proportion of regulatory T (Treg) cells in the CD4+ cells of large intestinal lamina propria lymphocytes (LPLs) was significantly increased (63% higher) at PD21 compared with PD14. The serum glucagon-like peptide (GLP)-1 tended to be lower (P = 0.0515) and that of GLP-2 was significantly lower (58% lower) at PD21 than at PD14. M-16V + LRG significantly increased the Treg proportion in large intestinal LPL CD4+ cells (20% and 29% higher compared with CON and M-16V, respectively) at PD14. M-16V + LRG also caused significant changes in expression of large intestinal mRNAs that are consistent with developmental progression, and increased serum concentrations of GLP-1 (207% and 311% higher compared with CON and M-16V, respectively) and GLP-2 (57% and 97% higher compared with CON and M-16V, respectively) at PD14. CONCLUSIONS: Neonatal administration of M-16V + LRG alters the gut microbiota and enhances gut immune and endocrine development in suckling mice.

El Niño Altered Gut Microbiota of Children: A New Insight on Weather-Gut Interactions and Protective Effects of Probiotic.

Changes in weather often trigger a myriad of negative impacts on the environment, which eventually affect human health. During the early months of 2016, Malaysia experienced El Niño, with an extremely dry season of almost zero rainfall. At the same time, an increase of more than twofold in fecal secretary immunoglobulin-A (SIgA) levels of healthy preschool children aged 2-6 years was observed, accompanied by an increase in phylum Bacteroidetes, predominantly attributed to genus Bacteroides and Odoribacter, which also positively correlated with fecal SIgA levels. Here, we present evidence to illustrate the detrimental effects of weather change on a microscopic "environment," the human gut ecosystem. We also discuss the protective effects of probiotic against dysbiosis as induced by weather change. The increase in Bacteroidetes was at an expense of decreased genus Faecalibacterium and Veillonella (phylum Firmicutes), whereas children consuming probiotic had a decrease in genus Collinsella, Atopobium, and Eggerthella (phylum Actinobacteria) instead.

Association between functional lactase variants and a high abundance of Bifidobacterium in the gut of healthy Japanese people.

Previous studies have shown that Japanese people exhibit a higher abundance of Bifidobacterium compared to people from other countries. Among the possible factors affecting the gut microbiota composition, an association of functional lactase gene variants with a higher abundance of Bifidobacterium in the gut has been proposed in some reports. However, no Japanese subjects were included in these studies. In this study, we investigated the possible contribution of functional lactase loci to the high abundance of Bifidobacterium in Japanese populations. Based on a data analysis assessing 1,068 healthy Japanese adults, a number of subjects is at least seven times greater than that reported in available online data. all subjects possessed CC genotype at rs4988235 and the GG at rs182549, which are associated with low lactase activity. We observed a positive correlation between dairy product intake and Bifidobacterium abundance in the gut. Considering previous reports, which revealed that four additional functional lactase loci, rs145946881, rs41380347, rs41525747 and rs869051967 (ss820486563), are also associated with low lactase activity in Japanese people, our findings imply the possible contribution of host genetic variation-associated low lactase activity to the high abundance of Bifidobacterium in the Japanese population.

Genomic diversity and distribution of Bifidobacterium longum subsp. longum across the human lifespan.

Bifidobacterium longum subsp. longum represents one of the most prevalent bifidobacterial species in the infant, adult and elderly (human) gut. In the current study, we performed a comparative genome analysis involving 145 B. longum representatives, including 113 B. longum subsp. longum strains obtained from healthy Japanese subjects aged between 0 and 98 years. Although MCL clustering did not reveal any correlation between isolated strains and subject age, certain characteristics appear to be more prevalent among strains corresponding to specific host ages, such as genes involved in carbohydrate metabolism and environmental response. Remarkably, a substantial number of strains appeared to have been transmitted across family members, a phenomenon that was shown not to be confined to mother-infant pairs. This suggests that the ubiquitous distribution of B. longum subsp. longum across the human lifespan is at least partly due to extensive transmission between relatives. Our findings form a foundation for future research aimed at unraveling the mechanisms that allow B. longum strains to successfully transfer between human hosts, where they then colonize and persist in the gut environment throughout the host's lifespan.

Therapeutic potential of Bifidobacterium breve strain A1 for preventing cognitive impairment in Alzheimer's disease.

It has previously been shown that the consumption of probiotics may have beneficial effects not only on peripheral tissues but also on the central nervous system and behavior via the microbiota-gut-brain axis, raising the possibility that treatment with probiotics could be an effective therapeutic strategy for managing neurodegenerative disorders. In this study, we investigated the effects of oral administration of Bifidobacterium breve strain A1 (B. breve A1) on behavior and physiological processes in Alzheimer's disease (AD) model mice. We found that administration of B. breve A1 to AD mice reversed the impairment of alternation behavior in a Y maze test and the reduced latency time in a passive avoidance test, indicating that it prevented cognitive dysfunction. We also demonstrated that non-viable components of the bacterium or its metabolite acetate partially ameliorated the cognitive decline observed in AD mice. Gene profiling analysis revealed that the consumption of B. breve A1 suppressed the hippocampal expressions of inflammation and immune-reactive genes that are induced by amyloid-ß. Together, these findings suggest that B. breve A1 has therapeutic potential for preventing cognitive impairment in AD.

Decreased Taxon-Specific IgA Response in Relation to the Changes of Gut Microbiota Composition in the Elderly.

Gut microbiota is known to change with aging; however, the underlying mechanisms have not been well elucidated. Immunoglobulin A (IgA) is the dominant class of antibody secreted by the intestinal mucosa, and are thought to play a key role in the regulation of the gut microbiota. T cells regulate the magnitude and nature of microbiota-specific IgA responses. However, it is also known that T cells become senescent in elderly people. Therefore, we speculated that the age-related changes of IgA response against the gut microbiota might be one of the mechanisms causing the age-associated changes of gut microbiota composition. To prove our hypothesis, fecal samples from 40 healthy subjects (adult group: n = 20, an average of 35 years old; elderly group: n = 20, an average of 76 years old) were collected, and the gut microbiota composition and the response of IgA to gut microbiota were investigated. The relative abundance of Bifidobacteriaceae was significantly lower, whereas those of Clostridiaceae, Clostridiales;f__ and Enterobacteriaceae were significantly higher in the elderly group than in the adult group. There was no significant difference in the fecal IgA concentration between the adult and elderly groups. However, the taxon-specific IgA response to some bacterial taxa was different between the adult and elderly groups. To evaluate inter-group differences in the taxon-specific IgA response to each bacterial taxon, the IgA-indices were calculated, and the IgA-indices of Clostridiaceae and Enterobacteriaceae were found to be significantly lower in the elderly group than the adult group. In addition, Clostridiales;f__ and Enterobacteriaceae were significantly enriched in the IgA+ fraction in the adult group but not in the elderly group, whereas Clostridiaceae was significantly enriched in the IgA- fraction in the elderly group but not in the adult group. Some species assigned to Clostridiaceae or Enterobacteriaceae are known to be pathogenic bacteria. Our results suggest the possible contribution of decreased IgA response in the increased abundance of bacterial taxa with potential pathogenicity in the intestinal environment of the elderly. Our findings contribute to the understanding of the regulatory factor for the changes in the gut microbiota composition with aging.

Age-Related Changes in the Composition of Gut Bifidobacterium Species.

Bifidobacteria are one of the major components in human microbiota that are suggested to function in maintaining human health. The colonization and cell number of Bifidobacterium species in human intestine vary with ageing. However, sequential changes of Bifidobacterium species ranging from newborns to centenarians remain unresolved. Here, we investigated the gut compositional changes of Bifidobacterium species over a wide range of ages. Faecal samples of 441 healthy Japanese subjects between the ages of 0 and 104 years were analysed using real-time PCR with species-specific primers. B. longum group was widely detected from newborns to centenarians, with the highest detection rate. B. breve was detected in approximately 70% of children under 3 years old. B. adolescentis and B. catenulatum groups were predominant after weaning. B. bifidum was detected at almost all ages. The detection rate of B. dentium was higher in the elderly than in other ages. B. animalis ssp. lactis was detected in 11.4% of the subjects and their ages were restricted. B. gallinarum goup was detected in only nine subjects, while B. minimum and B. mongoliense were undetected at any age. The presence of certain Bifidobacterium groups was associated with significantly higher numbers of other Bifidobacterium species/subspecies. Inter-species correlations were found among each species, exception for B. animalis ssp. lactis. These results revealed the patterns and transition points with respect to compositional changes of Bifidobacterium species that occur with ageing, and the findings indicate that there may be symbiotic associations between some of these species in the gut microbiota.

Antihypertensive effect of the bovine casein-derived peptide Met-Lys-Pro.

The antihypertensive effect of the bovine casein-derived peptide Met-Lys-Pro (MKP) was examined in vitro and in vivo. MKP showed angiotensin I-converting enzyme (ACE)-inhibitory activity in vitro (IC50 = 0.43 µM). An in vivo kinetics study using radiolabeled Met-[1-(14)C]Lys-Pro ((14)C-MKP) showed that orally administered (14)C-MKP to spontaneously hypertensive rats (SHRs) was absorbed and moved into the plasma. In vitro vasoconstriction of thoracic aorta preparations, which was induced by adding angiotensin I, was reduced by prior exposure of MKP. A single oral dose of MKP lowered systolic blood pressure (SBP) of SHRs, and repeated oral administration of MKP for 28 days significantly lowered SBP of SHRs. The results obtained in the present study suggest that orally administrated MKP can be absorbed into the plasma and its ACE-inhibitory activity may contribute to induce the antihypertensive effect in vivo.

Novel angiotensin I-converting enzyme inhibitory peptide derived from bovine casein.

Bovine lactic casein was hydrolysed using a combination of three enzymes, namely, subtilisin, bacillolysin, and trypsin, and the resulting preparation was coined CH-3. CH-3 showed angiotensin I-converting enzyme (ACE)-inhibitory activity (IC50: 74 µg/mL). A single oral administration of CH-3 led to a transient but significant decrease in the systolic blood pressure (SBP) of spontaneously hypertensive rats (SHRs), while daily oral administration of CH-3 for 28 consecutive days led to a lower rate of SBP increase. The CH-3 preparation was then fractionated and the αS2-casein-derived tripeptide Met-Lys-Pro (or MKP) was identified as a novel peptide with strong ACE-inhibitory activity (IC50=0.12 µg/mL, 0.3 µM). The MKP peptide constituted only 0.053% of CH-3 but its activity was accounted for 33% of the total ACE-inhibitory activity of CH-3. In addition, a single oral administration of MKP also led to a transient but significant decrease in the SBP of SHRs.