Science

More than 1,000 species including over 100 trillion gut microbes coexist and form varieties of microorganism-ecosystems in the human gut, which are referred to as gut microbiome. The gut microbiome has many kinds of physiological effects on the host that offer benefits for human health. For example, the lactic acid bacteria and Bifidobacterium are utilized to ferment milk, such probiotics—microorganisms offering health benefits—improve the balance of the human gut microbiome for the benefit of the host. However, we still do not have a complete understanding of the identities all the species and functions of gut microbes because many microorganisms are difficult to culture and cultivate.
But recent advances in molecular biological analysis technology based on base sequencing information— especially metagenomic analysis of gut microbiome with next-generation sequencing—and bioinformatics, has revealed that gut microbes are associated with illnesses inflicting their hosts. The latest studies show that microorganism and their metabolites (the term ‘postbiotics’ is used to refer to metabolic byproducts secreted by live microorganisms) affect obesity, typeⅡ diabetes ^1)-4), inflammatory bowel diseases ^{5), 6)} such as ulcerative colitis and Crohn’s disease, and mental disorders ⁷⁾ such as autism.
Accordingly, research on the gut microbiome has been recognized as one of the new effective approaches for prophylaxes, that is, treatment undertaken to prevent disease, with the result that there is increasing scientific research on understanding the gut microbiome from the viewpoint of clinical applications.

Reference
1) Ley, R.E. et al. Proc Natl Acad Sci USA 102, 11070-11075 (2005).
2) Turnbaugh, P.J. et al. Cell Host Microbe 3, 213-223 (2008).
3) Yoshimoto, S. et al. Nature 499, 97-101 (2013).
4) Wen, L. et al. Nature 455, 1109-1113 (2008).
5) Png, C.W. et al. Am J Gastroenterol 105, 2420-2428 (2010).
6) Li, Q. et al. PLoS One 7, e34939 (2012).
7) Finegold, S.M. et al. Anaerobe 16, 444-453 (2010).