The other paper from Chisholm's laboratory (lead authors are Zackary I. Johnson, now at the University of Hawaii, and Erik Zinser, now at the University of Tennessee), compares six known ecotypes, or subdivisions, of the Prochlorococcus microbes according to where they're found and under what conditions they thrive. Their geographic patterns suggest causal relations with environmental variables such as temperature, predators, light and nutrients.
Remarkably, despite centuries of oceanic research, tiny Prochlorococcus wasn't even known to exist two decades ago. It was discovered in 1985 during an open ocean research cruise by Rob Olson of the Woods Hole Oceanographic Institution and Chisholm.
Since then the science has progressed dramatically, and Chisholm can now describe Prochlorococcus in detail as "the smallest photosynthetic machine. It can convert the sun's energy into food through photosynthesis using only 1,700 genes, something the human body cannot do with 30,000 genes. In fact, despite all of our technological ingenuity, we cannot even mimic this process."
Chisholm, who is co-director of MIT's Earth System Initiative, explained that as biological oceanographers she and her colleagues are trying to understand the bio-geo-chemistry of the oceans. That is, they're trying to learn "how these microbes function as a system in which they have not only co-evolved with each other, but also with the chemistry and physics of the oceans. These three - chemistry, physics and biology - are tightly linked as a system, meaning you can't change one without altering the other two."
Such work is based on the discovery that seawater is absolutely loaded with invisible microbes. In trying to understand how this microbial system works, the MIT team has focused on Prochlorococcus as a model.