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Cyanobacteria convert nitrogen to usable nutrients, even in the near-boiling water of hot springs.

Devaki Bhaya

Cyanobacteria Work the Night Shift

Scientists have discovered to their surprise that a primordial, single-celled bacterium called Synechococcus has a rowdy nightlife. When night falls, Synechococcus stops photosynthesizing and begins converting nitrogen into usable nutrients for growth. The tiny microbe works its magic at near-boiling temperatures, providing the first example of a blue-green alga capable of juggling multiple forms of energy production in such an inhospitable environment.

Blue-green algae--also known as cyanobacteria--live in the harshest climates on Earth. From polar icecaps to desert hotsprings, the microbes survive by converting sunlight into energy. When the sun sets, they take a break and rely on their energy reserves for fuel. Some, however, plow through the night, converting nitrogen from the air into usable nutrients--a process known as nitrogen fixation. Up until now, scientists had only observed this hat trick at the outer--and cooler--edges of hotsprings.

To see if cyanobacteria can pull double duty at hotter temperatures, a team lead by biologists Devaki Bhaya, Anne-Soisig Steunou and Arthur Grossman of the Carnegie Institution in Palo Alto, California, collected samples of Synechococcus from two hotsprings in Yellow Stone National Park. The researchers then tracked the genes responsible for the microbe's energy and nutrient production.

Even in complete darkness at temperatures of up to 72°C Synechococcus keep on ticking. The researchers found that the organisms turned on three genes for an enzyme called nitrogenase, which aids nitrogen fixation. So why not fire up these genes during the day as well? The reason is that oxygen, a by-product of photosynthesis, poisons the nitrogenase, Bhaya notes. "It's no wonder the bacteria switch cycles after nightfall," she says. The team reports its findings online this week in Proceedings of the National Academy of Sciences.

It's clearly an entry for the algal-book-of-records. "The bacteria convert nitrogen into usable nutrients at a higher temperature than was previously thought possible," says Jonathan Trent, a microbiologist at the NASA AMES Center in Mountain View, California. This allows Synechococcus to have the best of both worlds, says Bhaya.

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