Dehalobacterium formicoaceticumis recognized for its ability to anaerobically ferment dichloromethane (DCM), and a catabolic model has recently been proposed.D. formicoaceticumis currently the only axenic representative of its class, theDehalobacteriia, according to the Genome Taxonomy Database. However, substantial additional diversity has been revealed in this lineage through culture-independent exploration of anoxic habitats. Here we performed a comparative analysis of 10 members of theDehalobacteriia,representing three orders, and infer that anaerobic DCM degradation appears to be a recently acquired trait only present in some members of the orderDehalobacteriales. Inferred traits common to the class include the use of amino acids as carbon and energy sources for growth, energy generation via a remarkable range of putative electron-bifurcating protein complexes and the presence of S-layers. The ability ofD. formicoaceticumto grow on serine without DCM was experimentally confirmed and a high abundance of the electron-bifurcating protein complexes and S-layer proteins was noted when this organism was grown on DCM. We suggest that members of theDehalobacteriiaare low-abundance fermentative scavengers in anoxic habitats.