Role of citrate as a complexing ligand which permits enzymically-mediated uranyl ion bioaccumulation

Journal Article · Thu Jun 01 04:00:00 EDT 1995 · Bulletin of Environmental Contamination and Toxicology

DOI:https://doi.org/10.1007/BF00197975· OSTI ID:61793

Yong, P; Macaskie, L E ^[1]

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1. Univ. of Birmingham (United Kingdom)

Microorganisms can be used to remove toxic heavy metals from liquid industrial wastes. One potentially useful system utilizes the enzymically-mediated biomineralization of heavy metals at the surface of bacterial cells. This well-documented system harnesses a metal-resistant phosphatase enzyme overproduced by a Citrobacter sp.; metal uptake is mediated by the activity of this enzyme, which persists in non-growing cells, to liberate HPO{sub 4}{sup 2-} from glycerol 2-phosphate with stoichiometric deposition of heavy metals(M) as cell-bound MHPO{sub 4}. Recent attention has focused on the treatment of wastes from nuclear power and nuclear fuel reprocessing activities, together with discharges of native uranium in mining wastes. Previous investigations using the Citrobacter sp. demonstrated removal of uranium and the transuranic elements, plutonium and americium. Although uranium is inhibitory to the growth of the Citrobacter strain, and the activity of the cellular phosphatase, uranyl phosphate accumulates as polycrystalline HUO{sub 2}PO{sub 4} at the cell surface. The rate of uranyl removal into the growing crystal is primarily dependent on the rate of phosphate release by the enzyme catalysed reaction. This is inconsistent with the reported toxicity of uranyl ion to the mediating phosphatase; however, in the presence of an excess of substrate, the rapid rate of phosphate release facilitated metal precipitation without toxic effect. Under substrate-limiting conditions uranyl toxicity was seen. The present investigation shows the inhibition of Citrobacter sp. phosphatase is related to the concentration of uranyl ion, and that citrate buffer can protect against this toxicity, and permit metal bioaccumulation. The toxicity pattern is dependent upon the substrate used; possible reasons for these effects, and environmental implications are discussed. 18 refs., 5 figs.

• OSTI ID: 61793
• Journal Information: Bulletin of Environmental Contamination and Toxicology, Journal Name: Bulletin of Environmental Contamination and Toxicology Journal Issue: 6 Vol. 54; ISSN 0007-4861; ISSN BECTA6
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
56 BIOLOGY AND MEDICINE
APPLIED STUDIES
BIOLOGICAL ACCUMULATION
BIOLOGICAL ADAPTATION
BUFFERS
CITRATES
ENZYMES
LIGANDS
RADIOACTIVE WASTES
REMEDIAL ACTION
TOXICITY
URANIUM COMPLEXES