Engineered Deinococcus radiodurans R1 with NiCoT genes for bioremoval of trace cobalt from spent decontamination solutions of nuclear power reactors
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The aim of the present work was to engineer bacteria for the removal of Co in contaminated effluents. Radioactive cobalt (60Co) 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 60Co (≥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 ~105-l spent decontamination solutions (SDS).
KeywordsBioengineering Bioremediation NiCoT genes Trace cobalt removal Spent decontamination solutions (SDS) Nuclear power reactors
The authors dedicate this manuscript to late Prof P. Maruthi Mohan. The authors thank Dr. Thomas Eitinger, Humboldt University, Germany, for providing the plasmids (pCH675-RP and pCH675-NA), K. W. Minton and M. J. Daly, Uniformed Services University of the Health Sciences, Bethesda, MD, for providing the D. radiodurans R1 strain, and M. E. Lidstrom, Departments of Chemical Engineering and Microbiology, University of Washington, Seattle, for providing the E. coli-Deinococcus shuttle vector pRAD1. We thank Deepti Appukuttan, who provided technical information related to Deinococcus transformation. We thank Dr. Venkata Prasuja Nakka, Department of Biotechnology and Bioinformatics, University of Hyderabad, Dr. Abdul Qadeer Mohammed, Department of Biochemistry, Osmania University, Hyderabad for their helpful suggestions and critical evaluation of the manuscript. The research work was supported by grants from the Department of Atomic Energy (No: 2004/37/17/BRNS), IFCPAR (3709-1), UGC-SAP (DRS-II), and INSPIRE Faculty Award (DST) IFA12-LSPA-11 to Raghu Gogada.
Conflict of interest
The authors declare that they have no conflict of interest.
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