( Scientists at the Carnegie Institution'...)Hot-spring bacteria flip a metabolic switch

Scientists at the Carnegie Institution's Department of Plant Biology have found that photosynthetic bacteria living in scalding Yellowstone hot springs have two radically different metabolic identities. As the sun goes down, these cells quit their day job of photosynthesis and unexpectedly begin to fix nitrogen, converting nitrogen gas (N2) into compounds that are useful for cell growth.

The study, published January 30 in the early online edition of the Proceedings of the National Academy of Sciences, is the first to document an organism that can juggle both metabolic tasks within a single cell at high temperatures, and also helps answer longstanding questions about how hot-spring microbial communities get essential nitrogen compounds.

Carnegie's Arthur Grossman, Devaki Bhaya, and Anne-Soisig Steunou, along with colleagues from four partner institutions*, are studying the tiny, single-celled cyanobacterium Synechococcus. Cyanobacteria evolved about three billion years ago, and are the oldest organisms on the planet that can turn solar energy and carbon dioxide into sugars and oxygen via photosynthesis. In fact, ancient cyanobacteria produced most of the oxygen that allows animals to survive on Earth.

Cyanobacteria such as Synechococcus are often found in the microbial mats that carpet hot springs, where life exists at near-boiling temperatures. These mats are highly organized communities where different organisms split up the work, with cyanobacteria serving as the main photosynthetic power plants. Microbial mats in Yellowstone National Park's Octopus Spring contain Synechococcus that can grow in waters up to around 160°F, while other microbes in the hot spring can tolerate temperatures that exceed 175°F. But until now, it was unclear which organisms could fix nitrogen--especially in the hotter regions of the mat.

"The cyanobacteria are true multitaskers within the mat community," Grossman said. "We had assumed that the single-celled c
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Source:Carnegie Institution

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