Interaction of Fe(III) reducing bacteria with heavy metals in contaminated soils Iron oxides are important metal sorbents and Fe(III) reducing bacteria (FeRB) can directly or indirectly alter the availability of metals in soils. The sediment subjacent to a former leaching heap and the bank soil of the creek Gessenbach in a former U mining district (Ronneburg Germany) showed high concentrations of metals and radionuclides both in the porewater and the solid phase. In this thesis i) the impact of FeRB on metal retention and ii) the tolerance of indigenous FeRB towards metal stress were investigated. In the sediment subjacent to the former leaching heap metal retention was likely not influenced by microbial activity due to low microbial abundance and activity and carbon limitation. In the creek soil metals were enriched in an iron rich horizon (Btlc) and in a sulfate rich horizon. Geochemical data indicated that Fe(III) reduction might be an important process in Btlc but reduction rates were low suggesting an inhibition of Fe(III) reduction in situ. In biostimulated soil slurries concentrations of soluble metals including U increased during Fe(III) reduction likely by desorption during reductive dissolution of Fe(III) oxides. The active Fe(III) reducing population as determined by stable isotope probing was dominated by  Proteobacteria (Geobacter) in 13C ethanol amended microcosms...