Bifidobacteria are biochemically anaerobic bacteria and mainly live in the intestine of humans and other mammals, insects, birds, etc. Currently, more than 100 species/subspecies of Bifidobacterium have been discovered, but their habitats differ depending on the species/subspecies. About 10 species live in the human gut（Human-Residential Bifidobacteria; HRB）, and only 4 to 5 are the natural colonizers in the gut of infant（infant-type HRB）. Our research group addressed the question, “Why do bifidobacteria live in the human gut and what do they do there?” We found that infant-type HRB are selected for by lysozyme as well as milk oligosaccharides（HMOs）in breast milk. These HRB species were found to be characterized by folate production, degradation of potentially harmful components in the infant gut, and production of aromatic lactic acids that may contribute to intestinal and systemic homeostasis. These findings shed light on the mechanisms by which HRB, especially infant-type HRB, exhibit adaptive and beneficial properties in the human gut.

On the other hand, growing bifidobacteria in yogurt and keeping them to remain viable for a long shelf-life is fraught with difficulties. This is due to the lack of free amino acids, vitamins, and other nutrients necessary for the growth of bifidobacteria in milk, as well as the presence of oxygen in the manufacturing and distribution process. This is especially true for HRB species, which are accustomed to living in the highly anaerobic human intestinal tract. Our research group has succeeded in developing a novel method of co-cultivation with strains of Lactococcus lactis, which has made it possible to produce yogurt containing high cell number and high survivability of bifidobacteria during distribution.

In recent years, the “brain-gut axis”, which refers to the bidirectional functional linkage between the gut and the brain, including intestinal bacteria, has attracted great attention. We have conducted research focusing on B. breve MCC1274 and found that intake of this probiotic strain significantly improved cognitive functions such as memory and spatial recognition and suppressed brain atrophy in older people suspected of having mild cognitive impairment. In addition, studies revealed that this probiotic strain suppressed the production of amyloid- β and showed anti-inflammatory effects in the brain as its mechanism of action. In addition, social implementation was realized as products such as yogurt and supplements for this strain.

In this review, by tracing the trajectory of research and development we have been involved in, I would like to introduce some topics related to basic, functional, and applied research on bifidobacteria.

It is expected that various diseases can be treated or prevented by controlling the intestinal microbiota, however, there are large individual differences in the response to microbiota-targeted interventions. This could be attributed to individual differences in the commensal bacterial community and competition among bacteria for nutrients. In this review, we discuss the significance of microscopic localization analysis of bacteria in elucidating the process by which individual bacteria acquire nutrients in a competitive environment. We used human stool sections to explore the localization of bacteria around food residues and found that Bifidobacterium adolescentis colonizes on starch granules in the intestine. This colonization was observed in every carrier of the species during ingestion of starch granules, and the species increased significantly and preferentially over other species upon the ingestion. The main bacterial species and the main organic acid that increased upon the ingestion differed by the presence or absence of the species, and the consumption efficiency of the starch granules in the intestine differed as well. These results indicate that bacterial colonization can contribute to the exclusive and efficient utilization of solid nutrients in the human gut, and that the effect of a nutrient on the gut and human body can vary depending on the presence or absence of the main colonizing bacterial species.

Lactic acid bacteria are representative intestinal bacteria. Lactobacilli have been shown to produce membrane vesicles (MVs) with a spherical structure that range in size between 20 and 200 nm in culture medium. Although MVs from lactobacilli appear to be composed of a cytoplasmic membrane, carry proteins and nucleic acids as cargoes, and stimulate host immune cells, biochemical analyzes of lactobacilli MVs have not been performed and there are many unclear points about their effects on host immune cells. Our group elucidated the physicochemical, biochemical and functional properties of MVs from Lactiplantibacillus plantarum JCM 8341. In this review, I summarize the characteristics and functions of lactobacilli MVs. Lactobacilli MVs play an important role in the crosstalk between gut microbiota and host immune cells and appear to be involved in maintaining homeostasis of the intestinal environment.

In recent years, the commensal microbiota in the intestine has begun to be called “another organ,” and it is believed that appropriate control of the commensal microbiota in the intestine can extend the healthy life span of humans. However, since more than half of the gene functions of intestinal commensal bacteria are not annotatable, there are many problems in controlling the intestinal environment at present.

For the purpose of solving the above problems, we developed a high-throughput culturing system for the most predominant species of the human intestinal commensal microbiota. First, of the 56 most predominant species of the human intestinal commensal flora, we demonstrated that 32 of the 44 available species could be grown on easily prepared GAM medium. This was 79% of the 44 available species among the 56 most prevalent species of the human intestinal commensal microbiota.

Next, we quantified polyamines in culture supernatants and bacterial cells of the most predominant species of commensal microbiota in the human intestine and compared the results with those expected from the genomic information, revealing the existence of many unknown metabolic and transport systems for polyamines. We also found that five of the most predominant species of commensal microbiota in the human intestine that are culturable in GAM produce large amounts of phenethylamine, which promotes the production of peripheral serotonin in the host.

Furthermore, using this system, we screened galactosyl- β-1,4-rhamnose, a “next-generation prebiotic” that is not utilized by the most dominant species of commensal microbiota in the human intestine but is utilized specifically by bifidobacteria. Additionally, we analyzed the effects of micronized okara on the growth and metabolic production of the most dominant species of commensal microbiota in the human intestine, and reported that the production of butyric acid by Roseburia intestinalis was enhanced by the addition of okara to the culture medium.

R Markdown is a recent mainstream way of executing R, consisting of R commands and a unique notation called Markdown. Its file extension is Rmd, which may not be familiar with many researchers, but is also used in our graduate educational and research program. We first describe the basic usage of R Markdown, including the concept of chunks and HTML generation. We next convert the contents of the previously created R script file into R Markdown and discuss the differences. Finally, we describe individual R commands and objects resulting from their execution in detail. Supplementary materials are available online at https://www.iu.a.u-tokyo.ac.jp/kadota/r_seq2.html.

We conducted an open-label, single-arm study on healthy Japanese subjects who were aware of thinning hair to investigate the effects of the treatment with Lactiplantibacillus plantarum subsp. plantarum N793（N793）-containing lotion on thinning hair. The subjects applied heat-sterilized N793-containing lotion for 24 weeks. For hair evaluation using a digital microscope, there was a significant improvement in hair density and non-vellus hair density at 24 weeks after treatment. The numbers of hair loss significantly decreased at 12 and 24 weeks after treatment. The score of hair loss in the VAS questionnaire significantly improved at 24 weeks after treatment. Similarly, the scores of hair thickness significantly improves 12 and 24 weeks after treatment. The scores of hair volume were significantly improved at 12 and 24 weeks after treatment, and the score of hairline and part was significantly improved at 24 weeks after treatment. The scores of subjective evaluation on hair loss were significantly improved at 12 and 24 weeks after treatment. There were no serious adverse events, and there were no changes that were suspected to be related to N793 treatment. These results suggest that the topical treatment of N793 improves thinning hair.