For scientists at MIT the smallest of all photosynthetic bacteria holds clues to the evolution of entire ecosystems, and perhaps even the whole biosphere. The key is a tiny bacterium called Prochlorococcus, which is the most abundant photosynthetic life form in the oceans. New research shows that this diminutive creature’s metabolism has evolved in a way that may have helped trigger the rise of other organisms, to form a more complex marine ecosystem. Its evolution may even have helped to drive global changes that made possible the development of Earth’s more complex organisms. The research also suggests that the co-evolution of Prochlorococcus and its interdependent co-organisms can be seen as a microcosm of the metabolic processes that take place inside the cells of much more complex organisms. The new analysis was published on March 27, 2017 in PNAS in a paper by MIT’s postdoc Rogier Braakman, Ph.D., Professor Michael Follows, and Institute Professor Sallie (Penny) Chisholm (photo), who was part of the team that discovered this tiny organism and its outsized influence. The PNAS article is titled “Metabolic Evolution and the Self-Organization of Ecosystems.” “We have all these different strains that have been isolated from all over the world’s oceans, that have different genomes and different genetic capacity, but they’re all one species by traditional measures,” Dr. Chisholm explains. “So there’s this extraordinary genetic diversity within this single species that allows it to dominate such vast swaths of the Earth’s oceans.” Because Prochlorococcus is both so abundant and so well-studied, Dr. Braakman says it was an ideal subject for trying to figure out “within all this diversity, how do the metabolic networks change?
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