narrator: maureen coleman has been studying the genetic composition of several prochlorococcus strains signatures in their genomes to suggest that viruses are actually important in moving genetic information between host cells. and this transfer of genetic information leads to diversification within the population. even though everything looks similar if you look at it under a microscope or in a culture tube -- they all look like small green cells -- it turns out that all of these prochlorococcus are actually quite different from each other. this is med-4, and the "med" stands for "mediterranean." so, this one has adapted to really high-light conditions in the oceans. and so, if you were to go out to the ocean, you would find a strain like med-4 at the surface -- so, right on the top layers of the water. and then, these other strains... um... these ones grow deeper, and these are low-light adapted. so, you wouldn't find these at 5 meters depth because they can't cope with the high light. but you might find these at 150 meters depth because they're much better at harvesting the very sma