Elusive Microbe Fertilizes Oceans

Nov. 14, 2008 -- After a long search researchers think they have found a cryptic microbe that helps fertilize ocean waters worldwide. Or at least they have found the single-celled critter's very telling and surprising genome.

The actual microbe -- a type of bacteria known as cyanobacteria -- has so far eluded direct observation, although perhaps not for much longer.

"This is a microscopic organism that I've been chasing for 10 years now," said researcher Jonathan Zehr of the University of California at Santa Cruz. "We couldn't culture it (in a laboratory) and couldn't see it." He is the lead author of a paper on the discovery featured in the Nov. 14 issue of the journal Science.

Hints of the mysterious organism have been popping up all over the world in DNA analysis of sea water, said Zehr. Those hints indicated that there was some small organism which was rigged to grab nitrogen from the air and feed the microscopic plants -- called phytoplankton -- that form the base of the ocean food chain. This makes it a rather important player in the oceans.

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"In order to pull down carbon dioxide from the atmosphere, we need phytoplankton," explained Woods Hole marine scientist Anton Post. And in order for sun-loving phytoplankton to grow, they need a host of nutrients -- just like land plants. "More often than not, nitrogen is the limiting nutrient."

Tracking down a widespread organism that gets nitrogen into the ocean food web has implications for global warming, which is driven by excessive carbon dioxide in the atmosphere.

By applying a powerful suite of new technologies to the task, Zehr and his colleagues were finally able to nail down the size and color of the organism and map out its genome. What they found was a shock.