Physiological Aspects of selenium oxyanion reduction and methylation by Rhodobacter sphaeroides 2.4.1

Verena Van Fleet-Stalder, Hakan Gurleyuk, and Thomas G. Chasteen

Department of Chemistry, Sam Houston State University, Huntsville, TX 77341-2117

Selected for two presentations at the 211th National American Chemical Society Meeting in New Orleans, March 24-28, 1996. One of 15 papers selected for this honor.

Rhodobacter sphaeroides 2.4.1 is a naturally occurring bacterium that has been shown to be resistant to considerable concentrations of metalloid oxyanions and to convert selenium oxyanions into methyl selenides when grown under anaerobic conditions in the presence of incandescent light. Capillary gas chromatography coupled with fluorine-induced chemiluminescence detection was used to study the release of methyl selenides and methyl sulfides by Rhodobacter sphaeroides over the course of time, at varied pH, and at varied selenium oxyanion concentrations. The highest amounts of organoselenium compounds were found in the late stationary phase of growth. A pH of 6 was optimal for the volatilization of selenate. With increasing selenate and selenite concentrations (up to 10 mM) the amounts of methyl selenides in the headspace increased too. However, the highest yields of reduced selenium found in dimethyl selenide and dimethyl diselenide per amount of selenium oxyanion added were found in cultures amended with 2 mM selenate and selenite.