Heterodisulfide reductase subunit A (HdrA) was the second most abundant selenoprotein family, which was represented by 10 selenoprotein genes. It is interesting that most of the HdrA sequences were found to cluster with FrhD sequences. This finding is consistent with our previous hypothesis that the hdrA-frhD-frhG-frhA cluster could be laterally transferred between Sec-decoding archaea and Deltaproteobacteria . A rhodanese-related sulfurtransferase [8 genes, ], AhpD-like (7 genes), Prx-like t...