Comparison of the hdr cluster of A. ferroooxidans ATCC 23270 (AF), Thioalkalivibrio sp. K90mix (K90) and Thioalkalivibrio sulfidophilus HL-EbGR7 (HL). The heterodisulfide reductase complex consists of the genes encoding HdrC1, HdrB1, HdrA, orf2, HdrC2 and HdrB2. The accessory proteins are Rhd, and TusA. DsrE was not found in this order, but was present at other places in the genome. The percentage of amino-acid similarity is indicated.