ENVIRONMENTAL BIOTECHNOLOGY Bioremediation of trace cobalt from simulated spent decontamination solutions of nuclear power reactors using E. coli expressing NiCoT genes G. Raghu & V. Balaji & G. Venkateswaran & A. Rodrigue & P. Maruthi Mohan Received: 6 May 2008 / Revised: 26 September 2008 / Accepted: 29 September 2008 / Published online: 24 October 2008 # Springer-Verlag 2008 Abstract Removal of radioactive cobalt at trace levels (≈nM) in the presence of large excess (10 6 -fold) of corrosion product ions of complexed Fe, Cr, and Ni in spent chemical decontamination formulations (simulated effluent) of nuclear reactors is currently done by using synthetic organic ion exchangers. A large volume of solid waste is generated due to the nonspecific nature of ion sorption. Our earlier work using various fungi and bacteria, with the aim of nuclear waste volume reduction, realized up to 30% of Co removal with specific capacities calculated up to 1 μg/g in 6–24 h. In the present study using engineered Escherichia coli expressing NiCoT genes from Rhodopseudomonas palustris CGA009 (RP) and Novosphingobium aromaticivorans F-199 (NA), we report a significant increase in the specific capacity for Co removal (12 μg/g) in 1-h exposure to simulated effluent. About 85% of Co removal was achieved in a two-cycle treatment with the cloned bacteria. Expression of NiCoT genes in the E. coli knockout mutant of NiCoT efflux gene (rcnA) was more efficient as compared to expression in wild-type E. coli MC4100, JM109 and BL21 (DE3) hosts. The viability of the E. coli strains in the formulation as well as at different doses of gamma rays exposure and the effect of gamma dose on their cobalt removal capacity are determined. The potential applica- tion scheme of the above process of bioremediation of cobalt from nuclear power reactor chemical decontamina- tion effluents is discussed. Keywords Bioremediation . Decontamination solution . NiCoT genes . Cobalt removal . Nuclear power reactors Introduction Power-generating nuclear reactors such as boiling water reactors, pressurized light water reactors, and pressurized heavy water reactors require chemical decontamination over a period of operation (Ayres 1970; Taylor 1976; Cohen 1980; Lejon et al. 1994). A major source of radiation field arises from the presence of activated corrosion product nuclides such as 51 Cr, 59 Fe, 58 Co, and 60 Co on the oxide-filmed inner surfaces of pipes and valves of equipment. 60 Co has proven to be a major contributor for person-sievert budgetary because of its long half-life 5.27 years and its high γ-energies (1.17 and 1.33 MeV), though the equivalent chemical concentration of total cobalt ( 59 Co + 60 Co) relative to that of Fe, Ni, and Cr when the Appl Microbiol Biotechnol (2008) 81:571–578 DOI 10.1007/s00253-008-1741-6 G. Raghu : P. Maruthi Mohan (*) Department of Biochemistry, Osmania University, Hyderabad 500 007, India e-mail: maruthipm@osmania.ac.in e-mail: maruthip@hotmail.com V. Balaji Water and Steam Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India G. Venkateswaran Analytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India A. Rodrigue Microbiologie, Adaptation et Pathogénie, Université de Lyon, Université Lyon 1, Lyon 69003, France A. Rodrigue CNRS, UMR 5240, INSA de Lyon, Villeurbanne 69621, France