Characterizing diversity and genetic exchange in marine Prochlorococcus

Marine Prochlorococcus is the most abundant photosynthetic organism on Earth, responsible for about 10% of global carbon fixation. It is a very diverse species with many layers of population structure. Despite the importance of the species, little is known about gene flow across its many scales of diversity. I will describe our recent efforts using hundreds of single cell genomes to elucidate a quantitative description of horizontal transfer of core genes in Prochlorococcus. These cells range from the most closely-related cells sequenced to date, whose genomes are largely asexual punctuated by discrete transfer events, to cells whose genomes have been overwritten and shuffled by recombination, to the most disparate Prochlorococcus cells, which are more than 50% diverged. We find that gene flow connects the entire species, identify the scale at which genomes become completely unlinked, estimate the distribution of recombination rates as a function of sequence divergence , and hope to connect these findings to ecology.