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 (SeO32-) to elemental selenium (Se-0). Enterobacter cloacae using glucose (1.4 mM) as an electron donor removed 79% of the added SeO32-(7.9 mu M) from solution in 2.5 h. Optimal SeO32- reduction occurred at a pH of 6.5 and a temperature of 40 degrees C. Carbohydrate sources arabinose, xylose, and sorbose were found to significantly enhance SeO32- reduction over that of glucose. The reduction of SeO32- at 7.9 mu 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 SeO32-. Enterobacter cloacae grows on anaerobically incubated plates containing NO3- as the sole terminal electron acceptor and acetate as the electron donor. Use of SeO32- as the terminal electron acceptor during anaerobic respiration did not support growth and could only be reduced to Se-0 when NO3- was present.