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Thriving in the Unsurvivable

Photo of USGS workers testing for arsenic in Searles Lake, CA.The findings of USGS Biochemist Ron Oremland are featured in an article in the May 27, 2005 issue of the journal Science. Oremland and his colleages discovered microbes living in extreme environmental conditions at Searles Lake located in the Mohave Desert of southeastern California. These microorganisms derive their energy for growth from metabolizing arsenic. While this was in itself not a new finding, their discovery that such a process occurs under the harsh chemistry of Searles Lake was a novel finding.

"This is a water body that is poised at salt saturation, about ten times saltier than seawater, but also with the added factor of being quite alkaline and thereby very caustic," Oremland said. "The pH of Searles Lakes is 9.8 and is therefore about 70-fold more alkaline than seawater. If you add in the unusually high concentrations of toxic arsenic in the water (about 4 mM) along with other harsh elements like boron, this is an environment that is definitely hostile to most forms of life. It’s a place where very few organisms can live. Sulfate-reduction and methane production do not occur in the anoxic sediments. What we discovered is that these microbes can exploit the dissolved arsenic in the lakewater in order to 'breathe'."

The new research points toward applications for arsenic remediation in other water sources. "Now that we’ve identified and isolated these bacteria, it will be interesting to see what analogous species with the same type of arsenic biochemistry are capable of doing in less extreme environments, such as freshwaters and drinking water aquifers" Oremland continued.

Photo of testing for arsenicThe newly-identified microbes also may add to the intrigue of potential life forms on other planets. "On planets like Mars and satellites like Europa, where their atmospheres lack oxygen and there is little organic matter present, past volcanic activity and the associated hydrothermal waters may have leached arsenic out of the rocks and concentrated it into saturated brines. Microbes such of the ones found at Searles Lake might have existed or might still exist entombed in salt-crystals," Oremland speculated. "At Searles Lake, conditions have become almost the opposite of what normally occurs in the earth’s crust, yet these microbes have found a way to make a living out of a very toxic element."



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