Microbiology

Arsenic-Metabolizing Bacteria in an Extreme Environment

The health of millions of people around the world is at risk from drinking well water contaminated with arsenic. In general, this arsenic has been found to occur naturally, rather than coming from identifiable point sources of pollution. With increasing evidence that mobilization of arsenic from subterranean geologic formations into the aqueous phase is a microbiological phenomenon, USGS scientists and others are conducting field and laboratory investigations to isolate arsenic metabolizing bacteria from diverse environments and to identify which specific microbiological mechanisms are responsible for arsenic dissolution.

In the journal, Science, USGS scientists reported the discovery of bacteria living in an environment which had conditions so extreme that it was assumed to be sterile. This arsenic-metabolizing bacterium, SLAS-1, was found in Searles Lake, California. Located in the Mojave Desert, Searles Lake is about ten times saltier and about 70-times more alkaline than seawater and contains arsenic in concentrations that are unusually high (about 4 mM). The bacteria isolated by the USGS scientists were found to not only tolerate the extreme conditions, but to derive energy from metabolizing arsenic. Through better understanding of these bacteria, the scientists are hoping to gain a better understanding of 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. In addition, the newly-identified microbes may provide information about potential life forms on other planets. Thus, this research has been supported in part by the National Aeronautics and Space Administration (NASA) since these studies may serve as a biogeochemical guide in the search for microbial life on planets like Mars and satellites like Europa.

For additional information, see 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. 1,305-1,308. or contact Ronald S. Oremland, roremlan@usgs.gov