Environmental Health - Toxic Substances Hydrology Program
A first glance at Searles Lake, California, one would assume that nothing could live in water that is ten times saltier and 70 times more caustic (alkaline, pH 9.8) than seawater, and is loaded with toxic arsenic (approximately 300 mg/L total arsenic). U.S. Geological Survey (USGS) scientists have shown that assumption to be wrong. The scientists have isolated a microorganism from Searles Lake that not only tolerates these ultra extreme conditions, but uses arsenic to "breathe." The microbes gain energy by reducing As(V) (arsenate) to the more toxic As (III) (arsenite) by transferring two electrons to the As(V) (arsenic is acting as an electron acceptor). Evidence for the opposite biochemical reaction, namely the use of As(III) as an electron donor with oxygen as the electron acceptor was also detected. The scientists hope this research will lead to an understanding of how similar microbes in less intense environments, such as a drinking-water aquifer, could be used to remove toxic arsenic from water. This could benefit many places around the world that are plagued with high concentrations of arsenic in drinking-water sources. These newly discovered microbes are also of interest to scientists that are looking for analogs here on earth for life forms on other planets. Dense brines similar to the waters of Searles Lake are hypothesized to exist on other planets or moons, such as within or below the Martian soils, or under the ice crust of Europa (a moon of Jupiter).
Oremland, R.S., Kulp, T.R., Blum, J.S., Hoeft, S.E., Baesman, S., Miller, L.G., and Stoltz, J.F., 2005, A microbial arsenic cycle in a salt-saturated, extreme environment: Science, v. 308, p. 1305-1308.