Engineered Deinococcus radiodurans R1 with NiCoT genes for bioremoval of trace cobalt from spent decontamination solutions of nuclear power reactors

Abstract

The aim of the present work was to engineer bacteria for the removal of Co in contaminated effluents. Radioactive cobalt ((60)Co) is known as a major contributor for person-sievert budgetary because of its long half-life and high γ-energy values. Some bacterial Ni/Co transporter (NiCoT) genes were described to have preferential uptake for cobalt. In this study, the NiCoT genes nxiA and nvoA from Rhodopseudomonas palustris CGA009 (RP) and Novosphingobium aromaticivorans F-199 (NA), respectively, were cloned under the control of the groESL promoter. These genes were expressed in Deinococcus radiodurans in reason of its high resistance to radiation as compared to other bacterial strains. Using qualitative real time-PCR, we showed that the expression of NiCoT-RP and NiCoT-NA is induced by cobalt and nickel. The functional expression of these genes in bioengineered D. radiodurans R1 strains resulted in >60 % removal of (60)Co (≥5.1 nM) within 90 min from simulated spent decontamination solution containing 8.5 nM of Co, even in the presence of >10 mM of Fe, Cr, and Ni. D. radiodurans R1 (DR-RP and DR-NA) showed superior survival to recombinant E. coli (ARY023) expressing NiCoT-RP and NA and efficiency in Co remediation up to 6.4 kGy. Thus, the present study reports a remarkable reduction in biomass requirements (2 kg) compared to previous studies using wild-type bacteria (50 kg) or ion-exchanger resins (8000 kg) for treatment of ~10(5)-l spent decontamination solutions (SDS).

Keywords: Bioengineering; Bioremediation; NiCoT genes; Nuclear power reactors; Spent decontamination solutions (SDS); Trace cobalt removal.