Magazine article Science News

Ocean Bacteria Need Iron with Dinner

Magazine article Science News

Ocean Bacteria Need Iron with Dinner

Article excerpt

Pumping iron to get big may be an activity most people associate with bodybuilders at the local gym, but the true champions of the art dwell in the world's oceans. There, phytoplankton bask in the sun's rays, absorbing carbon dioxide from the atmosphere and exhaling oxygen, while oceangoing bacteria scavenge organic matter from the water and breathe out carbon dioxide. Iron regulates the lives of both kinds of microorganisms, according to new research. Scientists learned 3 years ago that phytoplankton populations in iron-deficient waters grow tremendously when given a small dose of the trace mineral (SN: 3/5/94, p. 148). Few suspected, however, that the growth efficiency of oceanic bacteria is also ruled by iron, as Philippe Tortell and his colleagues at McGill University in Montreal report in the Sept. 26 Nature.

"Sure, there's a lot of phytoplankton," says Tortell, now at Princeton University. "But there are even more bacteria out there." Fifty percent of the organic carbon in oceans resides in bacteria. The researchers divided laboratory-grown colonies of bacteria into two batches and provided them with different amounts of iron but equal amounts of carbon.

Both colonies consumed their allotment of carbon, but the iron-deficient colonies grew more sparsely. The researchers added iron to the deficient colony, but the mineral failed to spur growth. Nor did carbon alone have an effect. Only when they increased both iron and carbon supplements did the bacteria start bulking up. …

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