That genome analysis, posted in the Proceedings of the National Academy of Sciences (PNAS) Online Early Edition July 25-29, reveals key biochemical tools that cold-adapted, or psychrophilic, bacteria can use to survive in subzero temperatures. In particular, some of C. psychrerythraea's estimated 4,937 genes apparently code for adaptive traits such as cell membranes packed with polyunsaturated fatty acids that resist freezing, polyester compounds that offer extra energy reserves, protective solutes inside cells, and ordinary enzymes altered to function in chilly seawater.
"Our goal was to compare C. psychrerythraea to a variety of bacteria that live at different optimal temperatures," remarks Barbara Methé, a molecular biologist at TIGR and lead author of the PNAS paper. "This organism must adapt to extreme cold--in fact, it cannot live above room temperature. How does it cope in such freezing conditions?"
Among cold-adapted bacteria, Colwellia species have a decidedly chilly comfort zone. The bacteria typically require temperatures less than 20° to grow. Scientists have found C. psychrerythraea--which prefers temperatures of -1° to 10° --hugging sediments along the Arctic floor, floating in the open ocean, and nestled inside Arctic and Antarctic sea ice.
To explain C. psychrerythraea's unique cold-adapted chemistry, TIGR researchers and collaborators first sequenced the bacterium's genome and analyzed its gene content for telltale proteins that might be cold-adaptive. Next, they predicted C. psychrerythraea's proteome--or complete inventory of protein sequences--and then compared it to 21 pred