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"Our analysis of the SAR11 genome indicates that they became the dominant life form in the oceans largely by being the simplest." Corvallis OR (SPX) Aug 19, 2005 Researchers at Oregon State University and Diversa Corporation have disco vered that the smallest free-living cell known also has the smallest gen ome, or genetic structure, of any independent cell - and yet it dominate s life in the oceans, thrives where most other cells would die, and play s a huge role in the cycling of carbon on Earth. In a publication today in the journal Science, scientists outlined the gr owing knowledge about SAR11, a group of bacteria so dominant that their combined weight exceeds that of all the fish in the world's oceans. In a marine environment that's low in nutrients and other resources, they are able to survive and replicate in extraordinary numbers a milliliter of sea water off the Oregon coast might contain 500,000 of these cells. "The ocean is a very competitive environment, and these bacteria apparent ly won the race," said Stephen Giovannoni, an OSU professor of microbiol ogy. "Our analysis of the SAR11 genome indicates that they became the do minant life form in the oceans largely by being the simplest." The new study outlines how SAR11 has one of the most compact, streamlined genomes ever discovered, with only 13 million base pairs the smallest ever found in a free living organism and a number that's literally tiny compared to something like the human genome. Every genetic part serves a purpose, more so than any other genome we've studied." The organism is able to survive as an unattached cell in a hostile enviro nment, has a complete set of biosynthetic pathways, and can reproduce ef ficiently by consuming dissolved organic matter. "By comparison, humans are mostly junk DNA, with large parts of the human genome having no important function," Giovannoni said. This type of genome streamlining, researchers say, appears to be a major factor in the evolutionary success of SAR11, which they believe may have been thriving for a billion years or more. One scientific hypothesis holds that natural selection acts to reduce gen ome size because of the metabolic burden of replicating "junk" DNA with no adaptive value SAR11 supports that theory. Researchers are particularly interested in SAR11, Giovannoni said, becaus e of the critical role it plays in geochemistry. Photosynthesis is a pro cess used by plants to convert sunlight energy into organic molecules, c reating the foundation of the food chain and producing oxygen. About half of photosynthesis and the resulting oxygen on Earth are produc ed by algae in the ocean, and microbes like SAR11 recycle organic carbon - producing the nutrients needed for algal growth. "Ultimately, SAR11 through its sheer abundance plays a major role in the Earth's carbon cycle," Giovannoni said. "Quite simply, this is something we need to know more about. SAR11 is a m ajor consumer of the organic carbon in the oceans, which nearly equals t he amount of carbon dioxide in the atmosphere. The carbon cycle affects all forms of plant and animal life, not to mention the atmosphere and fo ssil fuel formation." Since then researchers have le arned that populations of SAR11 increase during the summer and decrease during the winter, in a cycle that correlates to the ebb and flow of org anic carbon in the ocean surface. Molecular probes, gene cloning, sequen cing techniques and other tools have been used in this exploration.
Moss Landing CA (SPX) Jun 13, 2005 One of the biggest questions in modern oceanography is how animals in the deep sea get enough to eat. Marine biologists at the Monterey Bay Aquar ium Research Institute (MBARI) recently published a paper that helps ans wer this question, at least for animals that live on the deep seafloor o ff the coast of Central California. The contents herein, unless otherwise known to be public domain, are Copy right 1995-2005 - TerraDaily.
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