Gut Level Biodiversity

When people hear biodiversity, they tend to think of species in a large, outdoor habitat. But the basic concept of biodiversity—namely, that an ecosystem is most healthy when it contains a larger variety of individual species—can apply to just about any habitat. In the case of habitats such as the human body, it has implications for disease. Many bacterial infections can be viewed as caused less by the mere presence of a specific type of bacteria, but rather when a single species of harmful bacteria gets an upper hand on the rest and begins to overpopulate.

In an open access article at PNAS, researchers have looked at the biodiversity of the bacteria that live in the stomach of humans. They focused specifically on Helicobacter pylori, the bacteria that lead to ulcers, but cast their net quite widely. After sequencing over 1,800 individual samples from 23 people, they saw that the gut is home to more types of bacteria than expected (8 different phyla were found), including a few that had never been previously seen there. Intriguingly, different people seem to have different gut populations, suggesting that individual variation can alter the biodiversity there. It also appears that the stomach is a distinct environment relative to the mouth and esophagus.

From the disease perspective, it looks like Helicobacter pylori was the most common type of bacteria present in those individuals who had previously tested positive for it. But it is more widespread than previously thought, showing up at low levels in seven people who had not tested positive. It also looks like there is less bacterial diversity in the stomachs of those with high levels Helicobacter pylori. These findings reinforce the concept that it's the levels of the disease-causing bacteria relative to its harmless companions that's important, rather than its presence or absence.