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    Researchers Probe Ocean Bacteria

    By GAIL GALLESSICH

    Craig Carlson
    Scientists are still learning what's in a drop of ocean water, according to a recent report in Nature magazine. And the answers have implications for the whole planet, says coauthor UCSB oceanographer Craig Carlson, an assistant professor in ecology, evolution, and marine biology.
    "Microbes, like bacterioplankton, are important biogeochemical agents," explained Carlson. "Over geologic time, they have played an important role in altering the chemical nature of the Earth's environment, allowing for the evolution of plants and animals. Without them, we would have no oxygen to breathe, organic matter would not be degraded, and the cycling of life's essential nutrients would cease."
    About 10,000 bacterioplankton of the type SAR 11 are found in every drop of seawater. And yet, as explained in the article, which gives the first accurate quantitative assessment of SAR 11, scientists are only beginning to understand what these organisms do.
    The scientists found that the bacterioplankton SAR 11 comprises as much as 50 percent of the total surface microbial community (from zero to 140 meters below the surface) and 25 percent of the rest of the water column to the sea floor.
    "By sheer numbers, SAR 11 is important," Carlson said. "They are one of the most successful groups of bacteria in the ocean."
    The article is the result of collaboration between Carlson and his lab, and Stephen Giovannoni of Oregon State University (OSU) and his lab, including first author Robert Morris. The work was conducted under the Oceanic Microbial Observatory Project, a joint effort among UCSB, OSU and the Bermuda Biological Station for Research, which was initiated in 1999 by the National Science Foundation.
    For decades marine scientists have known that there are many types (species, strains) of bacterioplankton in the oceans. But their ability to distinguish one species from another in a quantitative manner was very limited. As a result, most oceanographers have treated bacterioplankton as a "black box."
    "We know that all bacterial species do not function the same way, so the 'black box' approach grossly oversimplifies microbial contributions," said Carlson. "One of the objectives of this study was to open up the black box and assess quantitatively how a specific group of bacterioplankton, called SAR 11, contribute to the total bacterial pool in the open ocean."
    SAR 11 were first identified in the early 1990s by Giovannoni from samples collected in the Sargasso Sea. Until development of fluorescent DNA probes in Giovannoni's lab, called "FISH" probes, their quantity and distribution in the ocean was unknown.