Microevolution and population dynamics of Prochlorococcus cells in the ocean: Insights through single-cell genomics

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Prochlorococcus is a bacterium that is widespread and abundant in the world oceans. As a photosynthetic cell, it uses sunlight to fix carbon dioxide into organic carbon, similar to plants on land. The global Prochlorococcus population in the oceans is made up of a diversity of "ecotypes," each of which has slightly different conditions for optimal growth. It is hypothesized that the diversity of this group of microbes allows it to thrive over broadly varying ocean habitats, but the genetic underpinnings of this diversity is very poorly understood. This research aims at advancing our understanding of the ecology and evolution of Prochlorococcus, by studying the genetic composition of single wild Prochlorococcus cells isolated from the Atlantic and Pacific oceans at different times of year. The study is motivated by two fundamental questions: (i) what is the relationship between the genetic composition of the cells and their ecological dynamics? (ii) how do populations adapt to their environment over ecological and evolutionary time scales?The broader significance of this work lies in the central role that Prochlorococcus plays in ocean ecology and the global carbon cycle. As the most abundant photosynthetic group in the oceans, Prochlorococcus is a critical component of the base of the food web. Because it conducts a sizable fraction of ocean photosynthesis, it plays an important role in the global carbon cycle and global climate processes. Understanding what regulates Prochlorococcus' diversity and dynamics is critical for developing predictive models of these important Earth system features.