Mössbauer investigations of solid phases that were formed during the reduction of amorphous synthesized ferrihydrite (SF) by thermophilic anaerobic iron-reducing bacterium Thermincola ferriacetica (strain Z-0001) and alkaliphilic anaerobic iron-reducing bacterium Geoalkalibacter ferrihydriticus (strain Z-0531) were carried out at room, liquid nitrogen and helium temperatures in the presence or the absence of an external magnetic field (6 T). The magnetization M (T, H) was measured in the temperature interval 80-300 K and magnetic field up to 10 kOe. It was performed zero field cooling (ZFC) and field cooling (FC) measurements of M (T).