HR: 16:45h
AN: U52C-04    [PDF]
TI: Not Just a Poison: Microbes That Derive Energy From Arsenic and Their Linkages to the C, N, and S Cycles.
AU: * Oremland, R S
EM: roremlan@usgs.gov
AB: Elements that are abundant in the Earth's crust and the microbes that derive energy from them have been the focus of much research in geomicrobiology. However, some trace elements also have significant biogeochemical cycles that are mediated by microorganisms, but the wider implications of these phenomena have generally been overlooked. This has been the case for arsenic. Arsenic is a toxicant owing to its action as an analog of its Group VB neighbor phosphorous. However, a surprising finding was that a wide diversity of anaerobic prokaryotes gain energy for growth by using arsenate as their electron acceptor, and that they are broadly distributed in nature. They carry out the dissimilatory reduction of arsenate to arsenite while oxidizing organic matter (or hydrogen). Since the electrochemical potential of the arsenate/arsenite couple is 60 mV, it acts as an oxidant of more reduced species like sulfide (- 220 mV). Some arsenate respirers oxidize sulfide, and in doing so fix CO2 into cellular material. Arsenite can be oxidized back to arsenate by aerobic chemoautotrophic microorganisms, or by anaerobes that use nitrate (440 mv). In addition, heterotrophic arsenate-respirers can carry out the reverse reaction, especially in arsenic rich environments like Mono Lake. The possible evolutionary significance of these phenomena and speculation about their occurrence elsewhere in the Solar System will be discussed.
DE: 0330 Geochemical cycles
DE: 4802 Anoxic environments
DE: 4803 Bacteria
DE: 4805 Biogeochemical cycles (1615)
DE: 4851 Oxidation/reduction reactions
SC: U
MN: 2003 Fall Meeting