Benzene is the main contaminant of an aquifer in the area of a former hydrogenation plan near Zeitz, Saxony-Anhalt. In its anoxic zone, investigations revealed an indigenous microbial consortium degrading benzene under sulfate-reducing conditions. A member of this consortium belongs to the Epsilonproteobacteria but its specific role remained unclear so far. One aim of this thesis was to clarify its function. The population genome of this species was reconstructed from a metagenome dataset and allowed an insight into its genetic capabilities. It revealed a microbe with a versatile metabolism potentially adaptable to various environments. Another part of this thesis dealt with the impact on the community by changing the terminal electron acceptor from sulfate to nitrate. For a microbe, nitrate is a thermodynamically more favorable electron acceptor compared to sulfate and thus, has the potential to accelerate the remediation of the contaminant plume. Indeed, the capability of benzene degradation was preserved under nitrate-reducing conditions and resulted in an altered community composition more adapted to the new redox conditions. Analysis on single-cell level allowed the identification of the new key microbes responsible for the degradation of benzene.