Biotransformation of uranium complexed with organic ligands

Natural ligands can affect the bacterial metabolism and reductive precipitation of uranium. The metabolism of metal-organic complexes by bacteria depends upon the type of complex formed between the metal and organic ligand. For example, Fe(III) forms a bidentate complex with citric acid, and was readily metabolized by

Pseudomonas fluorescens

under aerobic conditions, whereas the binuclear complex formed between U and citric acid was recalcitrant. When supplied with an electron donor, anaerobic bacteria reduced U(VI)-citrate to U(IV)- citrate with little precipitation of uranium. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy analysis showed that the reduced uranium was present in solution as mononuclear U(IV)-citrate complex. These results suggest that when reduced uranium is complexed with organic ligands, it can be mobile.