Microorganisms effects on radionuclides migration

In natural systems, speciation and migration of heavy metals and radionuclides depend on many factors such as pH, Eh and the presence of microorganisms. Microorganisms (bacteria, yeast, fungi) may have a direct action on the fate of metal ions through biosorption, bioaccumulation or resistance/detoxification processes. Microorganisms may influence the environment by producing mineral acids, chelating agents such as siderophore, or by-products from the metabolism (organic acids ...). In this paper, we report on microbial interaction processes including bioaccumulation, the indirect metal use for microbial life, the interaction with chelating agents, the resistance/detoxification mechanisms and some indirect influences of microorganisms on the speciation of metals. Also, we present some results of biosorption experiments with caesium, technetium, uranium, nickel and gadolinium using a variety of microbial strains. Saturation curves and Scatchard model were established for all biosorbants used in this work. For instance, the biosorption capacity for Gd3+ ranged from 350 µmol.g-1 for B. subtilis to 5.1 µmol.g-1 for S. cerevisiae. We found that biosorption could be influenced by the growth stage and by the composition of the growth medium of microbial cells. Finally, we will present some results of uranium reduction by subsurface sulfate-reducing bacteria. The reduced uranium precipitated as uraninite