Enzymatic U(VI) reduction by Desulfosporosinus species

Here we tested U(VI) reduction by a Desulfosporosinus species (sp.) isolate and type strain (DSM 765) in cell suspensions (pH 7) containing 1 mM U(VI) and lactate, under an atmosphere containing N-2-CO2-H-2 (90:5:5). Although neither Desulfosporosinus species (spp.) reduced U(VI) in cell suspensions with 0.25% Na-bicarbonate or 0.85% NaCl, U(VI) was reduced in these solutions by a control strain, Desulfovibrio desulfuricans (ATCC 642). However, both Desulfosporosinus strains reduced U(VI) in cell suspensions depleted in bicarbonate and NaCl. No U(VI) reduction was observed without lactate and H-2 electron donors or with heat-killed cells, indicating enzymatic U(VI) reduction. Uranium(VI) reduction by both strains was inhibited when 1 mM CuCl2 was added to the cell suspensions. Because the Desulfosporosinus DSM 765 does not contain cytochrome c(3) used by Desulfovibrio spp. to reduce U(VI), Desulfosporosinus species reduce uranium via a different enzymatic pathway.