APPLIED MICROBIAL AND CELL PHYSIOLOGY Characterization of technetium(vII) reduction by cell suspensions of thermophilic bacteria and archaea Nikolay A. Chernyh & Sergei N. Gavrilov & Vladimir V. Sorokin & Konstantin E. German & Claire Sergeant & Monique Simonoff & Frank Robb & Alexander I. Slobodkin Received: 16 September 2006 / Revised: 21 May 2007 / Accepted: 23 May 2007 / Published online: 7 July 2007 # Springer-Verlag 2007 Abstract Washed cell suspensions of the anaerobic hyper- thermophilic archaea Thermococcus pacificus and Ther- moproteus uzoniensis and the anaerobic thermophilic gram-positive bacteria Thermoterrabacterium ferrireducens and Tepidibacter thalassicus reduced technetium [ 99 Tc(VII)], supplied as soluble pertechnetate with molecular hydrogen as an electron donor, forming highly insoluble Tc(IV)-containing grayish-black precipitate. Apart from molecular hydrogen, T. ferrireducens reduced Tc(VII) with lactate, glycerol, and yeast extract as electron donors, and T. thalassicus reduced it with peptone. Scanning electron microscopy and X-ray microanal- ysis of cell suspensions of T. ferrireducens showed the presence of Tc-containing particles attached to the surfaces of non-lysed cells. This is the first report on the reduction in Tc(VII) by thermophilic microorganisms of the domain Bacteria and by archaea of the phylum Euryarchaeota. Keywords Technetium reduction . Tc(VII) reduction . Thermophilic microorganisms . Radionuclide immobilization Introduction Technetium ( 99 Tc), β-emitting fission product of 235 uranium has been released into the environment during nuclear weapon testing, uranium enrichment, nuclear fuel process- ing, and disposal after pharmaceutical use. The main source of Tc is the generation of nuclear power, where it is formed in quantities of 1–3 kg 99 Tc per ton of nuclear fuel. 99 Tc has been found in groundwaters and seawater near the sites of reprocessing or storage of nuclear wastes in USA, UK, and France. Tc is the critical radionuclide in determining the long-term environmental impact of the nuclear fuel cycle due to its long half-life (2.1×10 5 years) and the high mobility and bioavailability of pertechnetate ion (Wildung et al. 1979; Macaskie 1991, Peretruchin et al. 1996, Lloyd et al. 2002). One approach to remove 99 Tc from solution is to reduce Tc (VII) to insoluble low-valence forms. Enzymatic reduction in Tc(VII) under anaerobic conditions has been demonstrated for a number of mesophilic Fe(III)-reducing, sulfate-reducing, fermentative, and aerobic bacteria (Lloyd and Macaskie 1996; Lyalikova and Khizhnyak 1996; Lloyd et al. 1997, 1998; De Luca et al. 2001; Francis et al. 2002; Khijniak et al. 2003). Microbial processes of Tc(VII) reduction may occur in thermally insulated contaminated environments where tem- perature is elevated by the decay of long-lived radionuclides or in the subsurface depositories of nuclear waste due to Appl Microbiol Biotechnol (2007) 76:467–472 DOI 10.1007/s00253-007-1034-5 N. A. Chernyh : S. N. Gavrilov : V. V. Sorokin : A. I. Slobodkin (*) Winogradsky Institute of Microbiology, Russian Academy of Sciences, Prospect 60-letiya Oktyabrya 7/2, 117312 Moscow, Russia e-mail: aslobodkin@hotmail.com K. E. German Institute of Electrochemistry and Physical Chemistry, Russian Academy of Sciences, Leninskiy prospect 31, 119 991 Moscow, Russia C. Sergeant : M. Simonoff Laboratoire de Chimie Nucleaire Analytique et Bioenvironnementale, CNRS-Universite de Bordeaux I, UMR 5084, Le Haut Vigneau, BP 120, 33175 Gradignan Cedex, France F. Robb Center for Marine Biotechnology, 701 East Pratt Street, Baltimore, MD 21202, USA