Reduction of Selenite to Elemental Red Selenium by Pseudomonas sp Strain CA5

A Pseudomonas sp. that may be useful in bioremediation projects was isolated from soil. The strain is of potential value because it reduces selenite to elemental red selenium and is unusual in that it was resistant to high concentrations of both selenate and selenite. Exposure of the strain to 50, 100, and 150 mM selenite reduced growth by 28, 57, and 66%, respectively, while no change in growth was observed when the strain was exposed to 64 mM selenate, the highest level tested. Cells of the strain removed 1.7 mM selenite from the culture fluid during a 7-day incubation. A selenite reductase with a molecular weight of similar to 115 kD was detected in cell-free extracts and a protein with a molecular weight of similar to 700 kD was detected that reduced both selenate and nitrate. The bacterial isolate is a strict aerobe, reducing selenite to elemental red selenium under aerobic conditions only. Pseudomonas sp. strain CA5 might be useful as an inoculum for bioreactors used to harvest selenium from selenite-containing groundwater. 16S rRNA gene sequence alignment and fatty acid analysis were used to identify the bacterium as a novel species of Pseudomonas related to P. argentinensis, P. flavescens, and P. straminea.