The curated database of full length DsrAB sequences (n=274) was used to
construct a concatenated DsrA and DsrB phylogeny, as described
previously (11), that was congruent with previous phylogenetic
reconstructions of DsrAB (11, 23, 24). As previously documented,
recently discovered Euryarchaeote DsrAB formed a group with those from
Crenarchaeota, that together formed a basal-branching group among all
DsrAB (Figure 1). All organisms within this first group were recovered
from hydrothermal environments (largely hot springs) and their DsrAB are
inferred to be involved in HSO3- or
SO42- reduction (11). An additional
basal-branching second group comprised DsrAB recovered from uncultured
metagenome-assembled-genomes (MAGs) from various organisms and
environments, along with duplicate DsrAB copies within Moorellasp. genomes.
The remainder of DsrAB comprised a large group inclusive of both
reductive- and oxidative-type DsrAB that primarily includes bacterial
DsrAB. Within the “bacterial” group, homologs from Archaeoglobales
(Archaea) form a relatively early-evolving group, although the presence
of DsrAB in Archaeoglobales is thought to derive from a horizontal gene
transfer (HGT) event from a bacterial donor (22, 23). Lastly, theD. vulgaris homologs were present within a large cluster
comprising homologs from other putative and characterized
SO42- reducing Deltaproteobacteria.
Mapping of taxonomic information on to the DsrAB phylogenetic tree
revealed general concordance of DsrAB clades with their respective
taxonomic groups, consistent with previous analyses (23, 24). This
indicates that DsrAB are generally vertically inherited, although
several exceptions to this rule are evident including the example of
Archaeoglobales above. The mapping also revealed the broad range of
ecological contexts for SRO and their DsrAB. As documented previously
(11), DsrAB from organisms with subsurface and hydrothermal
environmental origins are particularly prominent near the root of the
tree, suggesting that the earliest DsrAB may derive from oxidant limited
and/or high temperature environments (45). However, general patterns of
ecological distributions beyond these early groups were not readily
apparent. This is likely attributable to the coarseness by which these
original environmental designations were assigned (i.e., by site of
isolation/sequence generation).