XPS and XANES Studies of Uranium Reduction by Clostridium sp

Abstract

Speciation of uranium in cultures of Clostridium sp. by X-ray absorption near-edge spectroscopy (XANES) at the National Synchrotron Light Source and by X-ray photoelectron spectroscopy (XPS) showed that U(VI) was reduced toU(IV). In addition toU(IV), a lower oxidation state of uranium, most probably U(III), was detected by XANES in the bacterial cultures. Reduction of uranium occurred only in the presence of growing or resting cells. Organic acid metabolites, the extracellular components of the culture medium, and heat-killed cells failed to reduce uranium under anaerobic conditions. The addition of uranyl acetate or uranyl nitrate (>210 µ U) to the culture medium retarded the growth of the bacteria as evidenced by an increase in the lag period before resumption of growth, by decreases in turbidity, and in the total production of gas and organic acid metabolites. These results show that uranium in wastes can be stabilized by the action of anaerobic bacteria.

U(VI) reduction by spores of Clostridium acetobutylicum

“…This is because, as reported by Francis et al (1994) and confirmed in this work, cell growth is inhibited by the presence of U(VI).…”

“…Cellular culture, growth and sporulation C. acetobutylicum (DSM 792) was obtained from DSMZ. It was grown anaerobically in a medium modified from Francis et al (1994), the main modification being a lower phosphate concentration to avoid uranium precipitation as a uranylphosphate phase. For this reason, we named the modified medium Francis low phosphate (FLP) basal medium, which is composed of (per liter): CaCl 2 , 0.5 g; K 2 HPO 4 , 0.03 g; NH 4 Cl, 0.5 g; MgSO 4 , 0.2 g; FeSO 4 , 2.8 mg; glucose, 5 g; glycerol, 0.25 mL; peptone, 0.1 g; yeast extract, 0.1 g. pH was set at 6.8, and cultures were incubated at 30 C.…”

“…One medium was spent FLP medium, which was collected at the end of exponential growth phase after the fermentative substrates had been completely converted to the final products: butyric acid, acetic acid, CO 2 and H 2 (Francis et al, 1994). The spent medium was amended with H 2 to compensate for loss of the gas during spent medium recovery.…”

“…However, these biochemical models may not apply to the whole spectrum of bacteria capable of this reaction, which comprises not only many other mesophilic Proteobacteria, but also Firmicutes e both sulfate-reducing and fermentative e e.g., Clostridium spp. (Francis et al, 1994), Desulfotomaculum spp. (Tebo and Obraztsova, 1998), Desulfosporosinus spp.…”

Bacterial community succession during in situ uranium bioremediation: spatial similarities along controlled flow paths

“…Clostridium spp. were shown to be able to reduce U(VI) (Francis et al, 1994;Madden et al, 2007) and similar populations were also detected in other OR-FRC sediments using glycerol-amended enrichments (Petrie et al, 2003). Clostridium populations were also suggested to be active members of the OR-FRC microbial community through a study of RNA-derived clone libraries (Akob et al, 2007), and low-G þ C bacteria have been isolated from OR-FRC groundwater (Fields et al, 2005).…”