The characterization of sulfate-reducing bacteria (SRBs) is presented using the dissimilatory sulfite reductase (dsrAB) gene from various samples capable of mineralizing petroleum components. These samples include several novel, sulfidogenic pure cultures which degrade alkanes, toluene, and tribromophenol. Additionally, we have sulfidogenic consortia which re-mineralize benzene, naphthalene, 2-methylnaphthalene, and phenanthrene as a sole carbon source. In this study, 22 new dsrAB genes were cloned and sequenced. The dsrAB genes from our pollutant-degrading cultures or consortia were distributed among known SRBs and previously described dsrAB environmental clones, suggesting that many biodegradative SRBs are phylogenetically distinct and geographically wide spread. Specifically, the same dsrAB gene was discovered in independently established consortia capable of benzene, phenanthrene, and methylnaphthalene degradation, indicating that this particular SRB may be a key player in anaerobic degradation of hydrocarbons in the environment.