Biotransformation of Uranium and Transition Metal Citrate Complexes by Clostridia

Abstract

Clostridium sphenoides, which uses citric acid as its sole carbon source, metabolized equimolar Fe(III)-citrate with the degradation of citric acid and the reduction of Fe(III) to Fe(II), but not the U(VI)-citrate complex. However, in the presence of excess citric acid or added glucose it was reduced to U(IV)-citrate. In contrast, Clostridium sp" which ferments glucose but not citrate, reduced Fe(III)-citrate to Fe(II)-citrate and U(VI)-citrate to U(IV)-citrate only when supplied with glucose, These results show that complexed uranium is readily accessible as an electron acceptor despite the bacterium's inability to metabolize the organic ligand complexed to the actinide. These results also show that the metabolism of the metal-citrate complex depends upon the type of complex formed between the metal and citric acid. Fe(III) forms a bidentate complex with citric acid and was metabolized, whereas U forms a binuclear complex with citric acid and was recalcitrant.

Soil Humic Acid Decreases Biological Uranium(VI) Reduction by Shewanella putrefaciens CN32

“…However, other soluble U(VI)-ligand complexes are readily bioreducible (Ganesh et al, 1997;Dodge and Francis, 1998;Francis et al, 2002), and the predicted extent of U(VI) complexation by SHA in these experiments is small. The Windemere Humic Aqueous Model (WHAM) with program default constants for U(VI) reactions with humic materials, hydroxide, and carbonate was used to predict that 16% of U(VI) would be complexed by 100 mg L Ϫ1 humic material for our experimental conditions (Tipping, 1994;CEH, 2001).…”

Reduction of Uranium(VI) to Uranium(IV) by Clostridia

“…(ATCC 53464) and Clostridium sphenoides (ATCC 19403) can reduce uranylnitrate, -acetate, and -citrate complexes as well as complexes of other metals, implying that the reduction of uranyl compounds is a general property of this genus (4)(5)(6). Apparently, Clostridium is one of major players in uranium reduction in situ in acidic (pH 4) uranium mine pit water (11,13), at a military facility near Chesapeake Bay, MD (1), and at the ORFRC at Oak Ridge, TN (8).…”

Immobilization of Uranium in Groundwater Using Biofilms

“…The mechanisms remain unclear; optimizing the conditions for fermentation resulted in better U(VI) reduction. [115,116,117] Clostridium pasteurianum Clostridium sp.…”