Reduction of Selenite to Elemental Selenium by Enterobacter cloacae SLD1a‐1

The facultative anaerobic bacterium Enterobacter cloacae strain SLD1a‐1 (ATCC‐700258) was studied in washed cell suspensions to assess optimal conditions required for the reduction of selenite (SeO 3 2− ) to elemental selenium (Se 0 ). Enterobacter cloacae using glucose (1.4 m M ) as an electron donor removed 79% of the added SeO 3 2− (7.9 m M ) from solution in 2.5 h. Optimal SeO 3 2− reduction occurred at a pH of 6.5 and a temperature of 40°C. Carbohydrate sources arabinose, xylose, and sorbose were found to significantly enhance SeO 3 2− reduction over that of glucose. The reduction of SeO 3 2− at 7.9 m M was inhibited by nitrate at levels 1 to 100 times greater, nitrite at levels 5 and 10 times greater, while sulfite at levels of two to four times greater was found to stimulate the reduction of SeO 3 2− . Enterobacter cloacae grows on anaerobically incubated plates containing NO 3 − as the sole terminal electron acceptor and acetate as the electron donor. Use of SeO 3 2− as the terminal electron acceptor during anaerobic respiration did not support growth and could only be reduced to Se 0 when NO 3 − was present.