Ocean-fertilising bacteria work together to adapt to light levels


Filaments of Trichodesmium can merge together to form an aggregate called a puff

Florida Fish and Wildlife Conservation Commission

One of the most abundant and important kinds of photosynthetic bacterium in the oceans may owe its success to teamwork.

The bacterium, called Trichodesmium, can actively join together to form large aggregates in response to changing environmental conditions, or split apart, Ulrike Pfreundt at ETH Zurich in Switzerland and her colleagues have discovered.

“This behaviour is possibly the key to why Trichodesmium is so abundant and so successful,” says Pfreundt.

Trichodesmium is a group of several species of cyanobacterium. Its members are sometimes called sea sawdust, as they often form reddish-brown blooms, which may have given the Red Sea its name.

These bacteria don’t just provide food for other organisms, they also turn nitrogen from the atmosphere into chemicals that other photosynthetic organisms can use. They fertilise vast areas of the ocean that would otherwise be too poor in nutrients for anything to grow, says Pfreundt.

“It’s the living fertiliser for the oceans, essentially,” she says. “They provide a very large part of the nitrogen that is fixed in the ocean, and a whole lot of other organisms that sequester CO2 depend on this nitrogen.”

Trichodesmium grows in hair-like filaments up to several hundred cells long. The filaments may be found floating around individually, but also often occur in colonies or aggregates, each containing up to several hundred filaments.

These aggregates can be 1 or 2 millimetres across, making them visible to the

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