Long-term corrosion in water-saturated conditions is the main factor responsible for the alteration of nuclear waste packages. However, the formation of passive layers (e.g. magnetite) on the metal surface can generally be considered a protective mechanism against corrosion. Understanding the impact of living microorganisms on the long-term durability of metallic packages is still an open issue, especially with regard to microbiologically influenced corrosion (MIC) processes. This study examines the impact of microbial activity on the reduction of structural Fe(III) in magnetite. The results demonstrate that such Fe oxides are available as electron acceptors using H 2 as electron donor for microbial metabolism, which may have a direct effect on the rates of corrosion.