Propionibacterium shermanii, an aerotolerant anaerobic bacterium, has already been shown to incorporate, depending on the metal supplementation to the medium, either iron or manganese or copper into the same superoxide dismutase protein. The in vivo incorporation of cobalt in the same superoxide dismutase was obtained in an iron-, manganese- and copper-depleted medium. The protein was isolated and characterized by NMR which offers the possibility to identify the amino acid residues at the active site exploiting isotropically shifted proton resonance.