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Colloquium – Gabriel Birzu, Stanford University
Do bacteria form species? Long term evolution leads to frequent hybridization in a natural microbial community
Genetic sequencing of natural bacterial populations often reveals distinct genomic clusters, which are usually interpreted as distinct species. At the same time, recent studies have shown extensive recombination across a wide range of genetic divergences, raising the question of how clusters can be maintained over time. Previous studies have shown that ecological separation can emerge within highly-recombining bacterial populations. However, whether this mechanism can prevent the hybridization and merging of distinct clusters is not known. Here, I show that thermophilic cyanobacteria from the Yellowstone National Park form a rare natural experiment to address this question. By analyzed a large collection of single-cell genomes, I demonstrate that despite their different ecologies, continual hybridization and natural selection have gradually eroded the genetic differences between clusters. These results suggest that ecological barriers cannot by themselves maintain genomic clusters over long evolutionary times and highlight the importance of spatial dynamics for maintaining microbial diversity.