Uranium sequestration by a marine cyanobacterium, Synechococcus elongatus strain BDU/75042

Abstract

A marine, unicellular cyanobacterium, Synechococcus elongatus strain BDU/75042 was found to sequester uranium from aqueous systems at pH 7.8. The organism could remove 72% (53.5 mg U g^-1 dry weight) of uranium from test solutions containing 100 μM uranyl carbonate within 1 h. The equilibrium data fitted well in the Langmuir isotherm thus suggesting a monolayer adsorption of uranium on the cyanobacterial biomass and predicted the maximum adsorption capacity of 124 mg U g^-1 dry weight. Light and scanning electron microscopy coupled with energy dispersive X-ray fluorescence (EDXRF) spectroscopy confirmed the uranyl adsorption by this organism. Most of the bound uranium was found to be associated with the extracellular polysaccharides (EPS) suggesting its interaction with the surface active ligands. Fourier transform infrared (FT-IR) spectroscopy suggested the amide groups and the deprotonated carboxyl groups on the cyanobacterial cell surface were likely to be involved in uranyl adsorption. The cell bound uranium could be released by washing with ethylene diamine tetraacetic acid (EDTA) or 0.1 N HCl. The X-ray diffraction (XRD) analyses revealed the identity of uranium deposits associated with the cell biomass as uranyl carbonate hydrate. The study revealed the potential of this cyanobacterium for harvesting uranium from natural aquatic environments.