T

he earth is teeming with microbes. There might be a trillion different species of bacteria on the planet, of which only .001 percent have been identified so far, according to new research in PNAS.

Here’s what Indiana University biologist Jay T. Lennon said about the new estimates and what they mean for the booming field of microbiome research.

What don’t we know about how many microbes are in humans?

There’s a lot of interest in trying to understand the types of microbes that are associated with the human microbiome and if they can ward off other pathogenic infections or do things like improve digestion. But we don’t really fully understand the diversity in those habitats and certainly not among individuals.

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We tried to develop scaling laws, trying to find some way to capture the abundance of microbes. Our study used human microbiome data, but it wasn’t the primary focus. But it can give us some expectations of how many types of bacterial species we’d see in a normal gut microbiome.

How do you predict the different types of bacteria present?

If you can tell me how many bacteria are in an individual habitat, then we can come up with powerful estimations of how many bacteria there would be in that environment. Theoretically, it’s a way of predicting aspects of diversity using one simple number: how many cells are in a sample.

How much diversity would you expect to see?

There’s a pattern we see no matter where we study, whether it’s the human gut or soil or the ocean. Systems tend to be dominated by just a few species of microbes, and then there are more rare species of microbes. It’s like crows and robins that you can see all day, but other types of birds are very rare and you encounter very infrequently. Those rarities are shared by microbial communities, and estimating them is a challenge.

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