The earth's most successful bacteria are found in the oceans and belong to the group SAR11. In a new study, researchers from Uppsala University in Sweden provide an explanation for their success and at the same time call into question generally accepted theories about these bacteria. In their analysis, they have also identified a rare and hitherto unknown relative of mitochondria, the power stations inside cells. The findings were published in two articles in the journals Molecular Biology and Evolution (September 7, 2011) and PLoS ONE (September 14, 2011). "The huge amounts of DNA information now being produced from the oceans gives us a glimpse of a world that could never be studied before. It's incredibly fascinating to look for answers to the fundamental questions of life in these data,” says Dr. Siv Andersson, professor of molecular evolution and senior author of the studies. Bacteria belonging to the group SAR11 make up 30-40 percent of all bacteria cells in the oceans and therefore play a considerable role in global carbon cycles. Nowhere else are these bacteria so common. The open seas are poor in nutrients, and SAR11 bacteria have an extremely small cell volume in order to maximize the concentration of nutrients in the cells. Their genomes are small, consisting of fewer than 1.5 million building blocks. According to previous research, they are related to an equally specialized group of bacteria that includes the typhus bacterium. These bacteria also have small genomes, but they are adapted to humans, animals, and insects. However, the advanced analyses of evolutionary relationships performed by the Uppsala researchers contradict these findings, indicating instead that SAR11 bacteria evolved from ocean- and earth-dwelling bacteria with genomes that are three to ten times as large.
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