Unravelling the determinants of microbial community diversity

Although photosynthetic bacteria are among the most abundant organisms on Earth, many microbial communities, including those living in the human gut and in the soil, rely on externally supplied carbon sources to survive and thrive. A major question is thus: do larger numbers of available resources mean more coexisting species? This is still largely unresolved because, traditionally, different facets of resource availability have been tackled separately, with theory focusing on the effects of the number of resources on species coexistence, and experiments concentrating on the impact of resource identity on community composition and function.

To fill this gap, we studied the assembly of hundreds of soil-derived microbial communities on a wide range of well-defined resource environments, from single carbon sources-including simple sugars, polysaccharides and organic acids-to combinations of up to 16. We showed that, while single resources supported multispecies communities varying from 8 to 40 taxa, mean community richness increased only one-by-one with additional resources. Cross-feeding, whereby the byproducts of microbial growth become food for other community members, could reconcile these seemingly contrasting observations. Specifically, the metabolic network seeded by the supplied resources explained the changes in richness due to both the identity and the number of resources, as well as the distribution of taxa across different communities. Finally, we used a consumer-resource model that incorporated the inferred cross-feeding network to provide further theoretical support to our observations and a framework to link the type and number of environmental resources to microbial community diversity.

You can read the full story here and soon on Nature Ecology & Evolution.

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