Nandita Garud presents “The Bacteria Within Us”

The human gut microbiome is composed of a complex ecosystem of microbes that reside inside of us and play an important role in our health. With estimates of as many as a billion new mutations entering our microbiomes per day, bacterial genomes inside us have a great opportunity to evolve rapidly. For us humans, this genetic dynamism is both an opportunity (e.g., enabling digestion of new foods) and a challenge (e.g. the evolution of drug resistance). Despite the potential importance of these effects, we currently know very little about if and how bacteria living in us evolve. With the availability of abundant whole-genome metagenomic data, we now have an opportunity to characterize the evolutionary forces of mutation, recombination, drift, migration, and adaptation shaping the microbiome. In my talk, I will present recent work quantifying the evolutionary dynamics of ~40 prevalent species of gut bacteria. We found that gut bacteria can evolve within humans on short timescales (~6 months), but over our lifetimes, resident bacteria are typically replaced by distantly related strains. These results suggest that gut bacteria can evolve on human-relevant timescales, but that there are limits to the extent of local adaptation.

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