Heterotrophic bacteria are key players in the biogeochemical cycle of iron in the marine environment. They modify the chemical speciation and therefore the bioavailability of iron, and they compete for the access to iron with other microorganisms. The capability of different bacterial groups to access various chemical forms of iron is, however, ignored thus far. Over the past few years microautoradiography was successfully applied to link bacterial diversity to the cycling of elements such as C, P and S. The aim of this study is to develop a similar approach based on the radioisotope 55Fe. I will present the first results of this technique applied to bacterial strains (Alteromonas macleodeii) grown under iron-controlled conditions, and to a natural community of heterotrophic bacteria collected in the NW Mediterranean Sea. I will discuss the potential, the difficulties and the limits of microautoradiography using 55Fe in the marine environment.