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The Subtle Beauty of Bacillus Subtilis (Part II)

A colorized electron micrograph image of actively growing rod-shaped Bacillus subtilis bacterial cells. The short ones are young cells which elongate as they grow up to a certain set size, at which point they initiate cell division at the cell center, constricting and splitting into two equal daughters. Beautifully simple, yet far from fully understood.

A colorized electron micrograph image of actively growing rod-shaped Bacillus subtilis bacterial cells. The short ones are young cells which elongate as they grow up to a certain set size, at which point they initiate cell division at the cell center, constricting and splitting into two equal daughters. Beautifully simple, yet far from fully understood.

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)

At least a thousand different species of microorganisms are natural residents of the (healthy) human gut alone; many other species are native to other habitats of the human body (e.g. mouth, nose, skin, genitals). [cartoon image from https://imes.mit.edu/about/news]

At least a thousand different species of microorganisms are natural residents of the (healthy) human gut alone; many other species are native to other habitats of the human body (e.g. mouth, nose, skin, genitals). [cartoon image from https://imes.mit.edu/about/news]

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...

NPR's Rob Stein narrates a story about the human microbiome, with animation by Benjamin Arthur and music and sound design by Jonathan Arthur.

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.

In terms of individual cell numbers, the human body houses TEN TIMES MORE MICROBIAL cells THAN HUMAN cells.  Of course microbial cells are way smaller than our own, so they are invisible and don't seem to take up much space. But in the gut, as much as 3 lbs./1.5 kg. of microbes may exist (2), and a significant portion of the mass of our poop is actually excreted dead gut bacteria.[cartoon from https://egtheory.wordpress.com/2014/12/12/microbiome/]

In terms of individual cell numbers, the human body houses TEN TIMES MORE MICROBIAL cells THAN HUMAN cells.  Of course microbial cells are way smaller than our own, so they are invisible and don't seem to take up much space. But in the gut, as much as 3 lbs./1.5 kg. of microbes may exist (2), and a significant portion of the mass of our poop is actually excreted dead gut bacteria.[cartoon from https://egtheory.wordpress.com/2014/12/12/microbiome/]

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.

Humans (other animals and plants, too) dependent on symbiotic microbes living inside us. (http://www.bio.davidson.edu/genomics/2014/Naso/gut.html)

Humans (other animals and plants, too) dependent on symbiotic microbes living inside us. (http://www.bio.davidson.edu/genomics/2014/Naso/gut.html)

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

Ann YonetaniComment