Sulfide assimilation in anaerobes: novel proteins for an ancient strategy

The metabolic network for sulfide assimilation and trafficking in methanogens is largely unknown. To discover novel proteins required for these processes, bioinformatic methods were used to identify genes co-occurring with the protein biosynthesis enzyme SepCysS, which converts phosphoseryl-tRNACys to cysteinyl-tRNACys in nearly all methanogens. The analyses revealed three conserved protein-coding genes, each containing molecular signatures predicting functions in sulfur metabolism. All three genes were also identified in more than 50 strictly anaerobic bacterial genera from nine distinct phyla.