Studies on the Physiological Functions of Bifidobacteria and Lactic Acid bacteria as well as Their Industrial Applications

Abstract

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.