( s are showing that all Prochlorococcus ...)MIT: Oceans are a major gene swap-meet for plankton

s are showing that all Prochlorococcus strains "are very closely related, yet they display quite an array of physiologies, and astounding genetic diversity on top of that," Chisholm said. It's becoming clear, too, that "this genetic diversity is at the heart of the extraordinary stability of Prochlorococcus in the oceans, which maintains steady population sizes over vast regions" of the sea.

The collective Prochlorococcus community merely adjusts internally, with different groups (genome types) waxing and waning in relative abundance, depending on who is most fit under ever-changing circumstances.

But how do they do it?

"We decided to let the cells tell us what is most important to them" by doing a systematic survey of relative abundances among six different types, or clades, of Prochlorococcus across vast environmental gradients in the oceans, Chisholm said. "We found first that two clades are orders of magnitude more abundant than all of the rest, and that temperature appeared to be very important in determining their distributions." Subsequent laboratory experiments with the cultured strains confirmed this idea.

Further analysis showed that most of the genetic differences between the two super-abundant strains are concentrated in a few "genomic islands," small zones where different kinds of genes get swapped in and swapped out, known among molecular geneticists as "hot spots" for gene exchange.

The distributors or carriers of new genes, they suspect, are the massive numbers of viruses also known to exist in seawater, some of which are adept at infecting ocean microbes such as Prochlorococcus. Such viruses, which carry genes of their own and sometimes transport odd genes picked up from an earlier host, are the most likely means of exchange - a natural way to get genes out of old cells and into new ones.

In essence, what all this means is that "our image of ocean microbes and their role in planetary maintenance is cha
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Source:Massachusetts Institute of Technology

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