Development of environmentally sustainable technologies for remediation of radionuclides is paramount because of their long-term persistence in different ecological niches and acute toxic and teratogenic effects on human, terrestrial and aquatic life. The radionuclides U (VI), Tc (VII), Pu (VI) and Np (V) are enzymatically reduced to environmentally benign U (IV), Tc (IV), Pu (IV) and Np (IV), respectively by anaerobic microorganisms for production of energy and/or as a process of detoxification for their survival. These anaerobic microorganisms produce the oxidoreductase class of enzymes for the metabolism of radionuclides. These microorganisms have potential applications for the in situ environmentally friendly mitigation of radionuclides in subsurface environments. Appropriate knowledge on the biochemical and genetic pathways of radionuclides reduction by microorganisms will not only provide information on the fate and dynamics of these compounds in subsurface geological environments but also help to implement best management practice(s) for immobilization of these toxic compounds in waste effluents generated by the mining and nuclear industries. This review describes the phylogenetic diversity of radionuclides-reducing microorganisms present in the environment, various enzymatic systems associated with the reduction of radionuclides, and identification of genes involved in regulation of different enzymatic redox reactions. (C) 2010 Elsevier Ltd. All rights reserved.