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Seafloor bacteria are multi-tasking with the carbon cycle

March 22, 2007

Scientists have long known that microorganisms can use one of two different methods to convert carbon dioxide into a form that living things can use for energy. What they didn’t know until recently is that at least one form of bacteria can switch between these two “carbon fixation” pathways or use them both at the same time—a fundamental discovery for scientists who believe such bacteria played a role in the evolution of life on Earth. Past research has shown that symbiotic bacteria live inside tubeworms and provide energy to their hosts in exchange for a safe place to live. Biologists knew this marriage was a good one, as the tubeworm is the fastest-growing marine invertebrate known to exist. But they did not know the details of how the bacteria make the energy because they could not culture the bacteria successfully in the lab. WHOI microbiologist Stefan Sievert was part of a research team—led by Thomas Schweder and Stephanie Markert of the Institute of Marine Biotechnology in Germany—that studied the bacteria’s genome to discover how these microbes switch back and forth between both carbon-fixing methods—the “Calvin cycle” and the reductive tricarboxyclic (rTCA) cycle—to adapt to fast-changing environmental conditions on the deep seafloor.