Résumé : Iron (Fe)- and manganese (Mn)-oxidizing bacteria are often cited individually and collectively as putative microorganisms for microbiologically influenced corrosion (MIC). The two groups of microorganisms have in common the ability to attach to surfaces and produce macroscopic accumulations (deposits) of metal oxides/hydroxides/oxyhydroxides that can influence corrosion of some metals and alloys in some environments. In all cases, once initiated, the corrosion is independent of the activities of the colonizing species. Despite the phylogentic diversity of Fe-oxidizing bacteria the following sections will deal with corrosion mechanisms attributed to neutrophilic, lithotrophic, microerophilic Fe-oxidizing bacteria (FeOB). The mineralogy of biologically oxidized Fe is consistent over a wide range of environments. All FeOB produce dense deposits that can cause corrosion of low alloy stainless steels directly, i.e., under deposit corrosion. Association of MnOB and other microorganisms may stabilize the under deposit corrosion on low alloy stainless steels. The influence of FeOB on the corrosion of carbon steel may be related to deposition of metal ions, causing galvanic corrosion or association with other corrosion-causing microorganisms. All MnOB produce manganese oxides that are strong naturally-occurring oxidizing agents that can cause ennoblement of low alloy stainless steels and increase corrosion currents on carbon steel in fresh water. Corrosion associated with manganese deposits depends on the relationship between the mineral deposit and the substratum.