THE USE OF ESCHERICHIA-COLI BEARING A PHON GENE FOR THE REMOVAL OF URANIUM AND NICKEL FROM AQUEOUS FLOWS

A Citrobacter sp, originally isolated from metal-polluted soil accumul ates heavy metals via metal-phosphate deposition utilizing inorganic p hosphate liberated via PhoN phosphatase activity. Further strain devel opment was limited by the non-transformability of this environmental i solate. Recombinant Escherichia coli DH5 alpha bearing cloned phoN or the related phoC acquired metal-accumulating ability, which was compar ed with that of the Citrobacter sp. with respect to removal of uranyl ion (UO22+) from dilute aqueous flows and its deposition in the form o f polycrystalline hydrogen uranyl phosphate (HUO2PO4). Subsequently, H UO2PO4-laden cells removed Ni2+ from dilute aqueous flows via intercal ation of Ni2+ into the HUO2PO4 lattice. Despite comparable acid phosph atase activity in all three strains, the E. coli DH5 alpha (phoN) cons truct was superior to Citrobacter N14 in both uranyl and nickel accumu lation, while the E. coli DH5 alpha (phoC) construct was greatly infer ior in both respects. Expression of phosphatase activity alone is not the only factor that permits efficient and prolonged metal phosphate a ccumulation, and the data highlight possible differences in the PhoN a nd PhoC phosphatases, which are otherwise considered to be related in many respects.