TheD. vulgaris sequence exhibits another insert in the DsrB subunit
(Figure 8, magenta), just prior to that observed in the A.
fulgidus sequence that makes contact with a different helix in the DsrA
subunit. This insert is missing in all early-branching DsrAB (Figure 9,
outer circle, purple) and is present in nearly all Deltaproteobacteria,
in addition to a few other lineages with evidence for HGT of DsrAB from
Deltaproteobacteria to other lineages (i.e., Thermodesulfobacteria and
some Firmicutes (23); Figure 9). Thus, this adaptation appears to have
evolved in the Deltaproteobacteria and has been retained throughout this
lineage, in addition to maintenance in other lineages following HGT.
These results suggest that these adaptations were a consequence of the
ecophysiological lifestyles of late-evolving Deltaproteobacteria.