The creatures that live inside you

Ecology is inside you. Since my undergraduate studies, I've always been interested in ecological phenomena that are close to people, something that everyone can experience without having to make long expensive journeys to the Okavango Delta or the Galapagos Islands. For some years now, our own inner ecosystem has been the focus of research for some microbiologists. Ecology is closer than ever. Interestingly, a new study shows that we carry somewhat different ecosystems in our gut.

A new article in Nature (Arumugam et al. 2011) describes the human inner ecosystem. There are eukaryotes (0.5%), archaea (0.8%) and viruses (5.8%) inside your digestive tract, but bacteria dominate by far. But it is not the same bacteria that dominate in all people.

For me as ecologist, it seems that our inner ecosystem works the same way as other classic ecosystem as rain forests or coral reefs. In general, more species is better than few. A rich diversity seems to make us less susceptible to infections and we get more out of the food we eat in the form of, for example, vitamins. Even how we feel may be affected quite directly by the bacteria in our stomach. But Arumugam and coauthors show in their Nature Article that we carry various internal ecosystem.

Bacteria are struggling for survival inside your digestive tract, caused by both the special environmental conditions and the sometimes severe competition from other microorganisms. This leads to a special distribution of organisms in the stomach and intestine, where some are common, while most of the species is rare.

You carry a complex ecosystem down there. We are not all the same, inside. Arumugam and co-authors found that there are three different kinds of bacterial diversity in the 33 persons surveyed in the study. The three groups are characterized by varying numbers of bacteria from the genera Bacteroides, Prevotella and Ruminococcus. So which group do you belong to?

Now that the bacteria have been shown to influence behavior in mice, it may be possible that our personality reflects our inner ecosystem? Should we include stomach and intestinal bacteria when we talk about our "I"? And from a more practical viewpoint, how does this influence our general well-being?