The Osamu Utsumi uranium mine, Poços de Caldas, Brazil is a roll front uranium deposit currently under investigation in an international natural analogue project involving Brazil, Sweden, Switzerland, the United Kingdom and the United States. This is a multi-disciplinary study (see the paper at this meeting by Smellie et al (1)), one component of which is an examination of the movement of natural series radionuclides across redox fronts. The processes at such fronts are analogous to those which could occur at radiolytic redox fronts found in the near- or far-field of deep repositories for HLW or spent fuel. Microbiological investigations have been carried out to determine the presence and activity of microbes known to be important in the uranium biogeochemical cycle; to define their importance in the movement of uranium across the redox front and to assess the significance of these observations to relevant safety assessment issues. This paper will summarise the results of these findings.