ABSTRACT
124In this research, selenate and selenite reduction by the aerobic bacterium Delftia lacustris was investigated and optimised. The selenate reduction profiles of D. lacustris were investigated by varying selenate concentration, inoculum size, concentration and source of organic electron donor in minimal salt medium. Although considerable removal of selenate was observed at all concentrations investigated, D. lacustris is able to completely reduce 0.1 mM selenate in 96 h using lactate as the carbon source. Around 62.2% unaccounted selenium, 10.9% elemental selenium and 26.9% selenite was observed in the medium after complete reduction of selenate. 77Se NMR spectroscopic analysis showed the unaccounted fraction of selenium was composed of selenium ester compounds. Delftia lacustris is reported for the first time as a selenate and selenite reducing bacterium, capable of tolerating and growing in more than 100 mM selenate and 25 mM selenite. Study of enzymatic activity of the cell fractions show that the selenite/selenate reducing enzymes were intracellular and independent of NADPH availability. D. lacustris shows unique metabolism of selenium oxyanions to form elemental selenium and water-soluble selenium ester compounds. This novel finding will advance the field of bioremediation of Se-contaminated sites and Se bio-recovery.
