Comprehensive analysis of the fecal microbiota of healthy Japanese adults reveals a new bacterial lineage associated with a phenotype characterized by a high frequency of bowel movements and a lean body type.

BACKGROUND: In Japan, a variety of traditional dietary habits and daily routines have developed in many regions. The effects of these behaviors, and the regional differences in the composition of the gut microbiota, are yet to be sufficiently studied. To characterize the Japanese gut microbiota and identify the factors shaping its composition, we conducted 16S metagenomics analysis of fecal samples collected from healthy Japanese adults residing in various regions of Japan. Each participant also completed a 94-question lifestyle questionnaire.

RESULTS: We collected fecal samples from 516 healthy Japanese adults (325 females, 191 males; age, 21-88). Heatmap and biplot analyses based on the bacterial family composition of the fecal microbiota showed that subjects' region of residence or gender were not strongly correlated with the general composition of the fecal microbiota. Although clustering analysis for the whole cohort did not reveal any distinct clusters, two enterotype-like clusters were observed in the male, but not the female, subjects. In the whole subject population, the scores for bowel movement frequency were significantly correlated with the abundances of Christensenellaceae, Mogibacteriaceae, and Rikenellaceae in the fecal microbiota (P < 0.001). These three bacterial families were also significantly more abundant (P < 0.05 or 0.01) in lean subjects (body mass index (BMI) < 25) than in obese subjects (BMI > 30), which is consistent with previously published results. However, a previously reported correlation between BMI and bowel movement frequency was not observed. In addition, the abundances of these three families were positively correlated with each other and comprised a correlative network with 14 other bacterial families.

CONCLUSIONS: The present study showed that the composition of the fecal microbiota of healthy Japanese adults at the national level was not strongly correlated with subjects' area of residence or gender. In addition, enterotype partitioning was ambiguous in this cohort of healthy Japanese adults. Finally, the results implied that the abundances of Christensenellaceae, Mogibacteriaceae, and Rikenellaceae, along with several other bacterial components that together comprised a correlative network, contributed to a phenotype characterized by a high frequency of bowel movements and a lean body type.