The New York Times has just run a story by Nicholas Wade, 6 Tribes of Bacteria Found to Be at Home in Inner Elbow. The piece discusses new views on commensal bacteria, types of bacteria that live benignly on the body of a host. As the article points out, DNA culturing has really expanded our ability to study these bacteria because they are so difficult to sample and culture normally (in part because they need their host to live very long). The research is part of the federally funded human microbiome project, an attempt to catalogue all of the bacterial DNA that makes up the human ‘microbiome’ or what some call the human ‘super-organism’ (not because it can leap tall buildings but because a human ‘being’ turns out to be a walking system with staggering numbers of bacterial ‘beings’ as part of it).

Usually, articles like this make the point that, ‘no matter how hard you wash, every square inch of you is still covered in millions of bacteria…’ This article is no exception. But the article is also working with a lot more interesting data. For example: ‘The project is in its early stages but has already established that the bacteria in the human microbiome collectively possess at least 100 times as many genes as the mere 20,000 or so in the human genome.’ Bacteria cells outnumber the cells of the body itself as they are often quite a bit smaller than human cells.

The human organism depends upon the bacteria that are along for the ride for all sorts of things, especially in processing food. I was especially struck by the following three paragraphs:

Other researchers have found that most gut bacteria belong to just 2 of the 70 known tribes of bacteria. The gut bacteria perform such vital services as breaking down complex sugars in the diet and converting hydrogen, a byproduct of bacterial fermentation, to methane.

The nature of the gut tribes is heavily influenced by diet, according to a research team led by Dr. Ruth E. Ley and Dr. Jeffrey I. Gordon of the Washington University School of Medicine in St. Louis. With the help of colleagues at the San Diego and St. Louis zoos, they scanned the gut microbes in the feces of people and 59 other species of mammal, including meat eaters, plant eaters and omnivores. Each of these three groups has a distinctive set of bacteria, they report in Friday’s issue of Science, with the gut flora of people grouping with the other omnivores.

Despite the vast changes that people have made to their diet through cooking and agriculture, their gut bacteria “don’t dramatically depart in composition from those of other omnivorous primates,” Dr. Gordon said.

I was curious about the similarity with other omnivorous primates, but also with the way that these colonies of commensal bacteria, vital for healthy digestion, might contend with changes in human diet brought about by technology. Yesterday, while driving around, I was listening to some fears by Greens in Germany about the introduction of nanoparticles to food without labeling.

I’m not necessarily more worried about nanoparticles than I am about the other chemicals that are being introduced into food, genetically-modified food, and other artificial enhancements. Are these new foods tested, not just on humans, but on necessary commensal bacteria (other than indirectly through human tests)?

In addition, there’s just the fascinating point for neuroanthropologists that ‘culture,’ in the sense of human variation, might inhere, not just in the minds and bodies of its human ‘carriers,’ but also in all the other organisms along for the ride. For example, we tend to look for human genetic explanations for different disease rates or for the causes of high obesity or diabetes rates in certain populations, but might part of the explanation be shifts in commensal bacteria populations? That is, might a human population not accustomed to certain industrialized foods experience difficult adjusting to a change in diet because their commensal bacterial population experiences difficulty adjusting?