Delftia lacustris is reported for the first time as a selenate and
selenite reducing bacterium, capable of tolerating and growing
in the presence of ≥ 100 mM selenate and 25 mM selenite.
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. Interestingly, the bacterium was able to reduce
both selenate and selenite under aerobic conditions. Although
considerable removal of selenate was observed at all concentrations
investigated, D. lacustris was able to completely reduce
0.1 mM selenate within 96 h using lactate as the carbon
source. Around 62.2% unaccounted selenium (unidentified
organo-selenium compounds), 10.9% elemental selenium
and 26.9% selenite were determined in the medium after
complete reduction of selenate. Studies of the enzymatic
activity of the cell fractions show that the selenite/selenate
reducing enzymes were intracellular and independent of
NADPH availability. D. lacustris shows an unique metabolism
of selenium oxyanions to form elemental selenium and
possibly also selenium ester compounds, thus a potential candidate
for the remediation of selenium-contaminated wastewaters
in aerobic environments. This novel finding will advance
the field of bioremediation of selenium-contaminated
sites and selenium bio-recovery and the production of potentially
beneficial organic and inorganic reactive selenium
species.