The use of Escherichia coli bearing a phoN gene for the removal of uranium and nickel from aqueous flows

Abstract

A Citrobacter sp. originally isolated from metal-polluted soil accumulates heavy metals via metalphosphate deposition utilizing inorganic phosphate liberated via PhoN phosphatase activity. Further strain development was limited by the non-transformability of this environmental isolate. Recombinant Escherichia coli DH5 alpha bearing cloned phoN or the related phoC acquired metal-accumulating ability, which was compared with that of the Citrobacter sp. with respect to removal of uranyl ion (UO2(2+)) from dilute aqueous flows and its deposition in the form of polycrystalline hydrogen uranyl phosphate (HUO2PO4). Subsequently, HUO2PO4-laden cells removed Ni2+ from dilute aqueous flows via intercalation of Ni2+ into the HUO2PO4 lattice. Despite comparable acid phosphatase activity in all three strains, the E. coli DH5 alpha (phoN) construct was superior to Citrobacter N14 in both uranyl and nickel accumulation, while the E. coli DH5 alpha (phoC) construct was greatly inferior in both respects. Expression of phosphatase activity alone is not the only factor that permits efficient and prolonged metal phosphate accumulation, and the data highlight possible differences in the PhoN and PhoC phosphatases, which are otherwise considered to be related in many respects.

Biomineralization of Uranium by PhoY Phosphatase Activity Aids Cell Survival in Caulobacter crescentus

“…S2 in the supplemental material) (18). Nevertheless, PhoY and PhoK belong to a group that is clearly distinct from acid phosphatases (e.g., PhoN in Salmonella enterica) that have been implicated in U biomineralization as well as other annotated phosphatases in C. crescentus (17,19,20).…”

“…BSAR-1, Arthrobacter, Rahnella, and Bacillus has been found to facilitate U(VI) precipitation through the formation of uranium phosphate complexes (17)(18)(19). Phosphatases from these organisms have been cloned and expressed in Escherichia coli and other organisms, and the resulting engineered strains have been reported to efficiently precipitate uranium (20)(21)(22). Among all these systems, however, little attention has been paid to the cellular benefits of the native or heterologously expressed phosphatases toward U(VI) resistance.…”

Engineering ofDeinococcus radioduransR1 for Bioprecipitation of Uranium from Dilute Nuclear Waste

“…4B). Both clones removed more than 90% of the uranium from solutions containing 0.8 mM uranyl nitrate in about 6 h. This is much superior to the uranium precipitation ability reported for native Citrobacter strains (strain N14, PhoN activity of 400 to 500 U and 37 to 61% uranium precipitation in 6 h; strain dc5c, PhoN activity of 850 U and 58% uranium precipitation in 6 h) under similar experimental conditions (10,20) for an engineered and immobilized E. coli strain expressing PhoN (PhoN activity of 100 to 150 U and 98% uranium precipitation in 400 h) (1). While E. coli cells (both wild type and transformants) showed considerable radiosensitivity, the transfer of phoN to Deinococcus radiodurans did not compromise its radioresistance (Fig.…”

“…and recombinant Escherichia coli expressing multiple copies of a nonspecific periplasmic acid phosphatase (PhoN) (10) have been reported to precipitate heavy metals efficiently (1,19). PhoN hydrolyzes organic phosphates, and the inorganic phosphate, thus released, interacts with the metal and precipitates it on the cell surface as insoluble metal phosphate (12,19).…”

Biochemical Characterization of an Acid Phosphatase fromThermus thermophilus

“…8,13) For instance, bacterial NSAP is involved in heavy metal accumulation, particularly in Citrobacter sp., therefore it can potentially be used as a tool for environmental bioremediation. 14,15) In addition, NSAP gene fusions have been exploited as targets for insertional inactivation in plasmid vectors for direct identification of recombinant clones. 16) Alternatively, bacterial nonspecific acid phosphatase alone or in combination with phytase can be used as feed supplements in the livestock industry to hydrolyze phytate into myo-inositol and phosphoric acid.…”