Bacillus subtilis is an old friend.
The species of bacteria used to create natto, Bacillus subtilis, has long been known as a common soil- and grass-dwelling microbe around the world. Only quite recently, have scientists recognized that another one of its natural habitats is within the gut of humans (1) as well as ruminant (grass-eating) mammals. Bacillus subtilis is a member of our human microbiome (the rich community of benign microorganisms living in/on us).
The human digestive system, particularly the intestinal tract, is home to a huge and diverse community of microorganisms, mostly bacteria. We live in symbiosis with these "good" microbes, collectively referred to as our "microbiome" (or microbiota) (2). It is believed that at least a thousand different species of bacteria reside in the healthy human gut (3), helping us to digest, access and even produce essential nutrients from the food we eat. An active area of scientific research is studying how our microbiome also affects many other diverse functions in the body including appetite and weight regulation, immune system function (relating also to autoimmune disorders & cancer) and even mental health. This NPR (National Public Radio) video gives a nice introduction to the subject...
In the past, many of these microorganisms regularly entered our bodies via naturally-grown and fermented foods which contain many benign bacteria. As the human diet becomes less diverse* (in terms of ingredients--species and varietals of plants & animals we gather, cultivate and consume) and more sterile (literally sterilized to eliminate pathogenic/ "bad" microbial contaminants and to promote commercial shelf life of processed foods), the health and diversity of our microbiome suffers.
A general recognition of this problem has been accompanied by a proliferation of probiotic supplements and food additives, but it is unclear how much (if any) benefit these provide (4). Most "probiotic" food products contain only one or a small number of commercialized species of these organisms, at very low concentrations, and possibly dead after extended shelf time. It is highly unlikely that any of these probiotic bacteria will survive the digestive process (corrosive stomach acid and anaerobic conditions) and actually make it alive to colonize the intestine. Expensive probiotic supplement capsules do contain a much larger dose and varied array of probiotic organisms but, again, when delivered in a (highly compromised) freeze-dried powdered form, it is unclear how many of them will actually live to see your gut.
Doesn't it makes much more sense to address both the problem and the solution at the same time by trying to add a greater diversity of naturally-grown, unprocessed, living foods to our diet? Freshly fermented foods contain much (many orders of magnitude) higher concentrations of more diverse strains of healthy, live probiotic bacteria than do industrially-produced "probiotic" products. By changing the way that we eat, we can help restore and preserve the universes of microorganisms that live inside of each one of us.
References: (1) Hong, H. A. et al. (2009) Bacillus subtilis isolated from the human gastronintestinal tract. Research in Microbiology. 160 (2):134-143. (2) Wikipedia [microbiome/microbiota] (3) Eckburg PB, Bik EM, Bernstein CN et al. (2005). "Diversity of the human intestinal microbial flora". Science 308 (5728): 1635–8. (4) Don't Be Fooled: 5 Probiotic Myths. http://www.livescience.com/46661-probiotics-myths.html.
* Many other reasons contributing to the current disruption of the human microbiome, to be addressed in future posts