Bacteria from Leptothrix genus were cultivated in Lieske's medium in presence of metallic lamellae (Al foil onesided covered by anodic Al2O3) in order to obtain supported gamma-FeOOH as a biogenic precursor of catalytically active gamma-Fe2O3. Samples were studied by the methods of infrared, Moessbauer, and X-ray photoelectron spectroscopy and scanning electron microscopy (with energy dispersive X-ray analysis). Among possible FeOOH modifications, only the deposition of gamma-FeOOH on the lamellae was attributed to the gamma-AlOOH ingredient in the used support because of crystal structure similarity. Different amounts of biogenic iron (0.6 and 0.9%) were deposited. The catalytic activity in the reaction of CO oxidation was examined by in situ diffuse-reflectance infrared spectroscopy. Changes of lepidocrocite to maghemite occurred during the catalytic experiments. Static CO adsorption measurements showed formation of carbonate (bidentate, monodentate) and formate species on the surface indicating that the oxidation occurs at room temperature by reaction of CO with surface or subsurface oxygen.