Novel nitrite reductase domain structure suggests a chimeric
denitrification repertoire in Phylum Chloroflexi
Denitrification plays a central role in the global nitrogen cycle,
reducing and removing nitrogen from marine and terrestrial ecosystems.
The flux of nitrogen species through this pathway has a widespread
impact, affecting ecological carrying capacity, agriculture, and
climate. Nitrite reductase (Nir) and nitric oxide reductase (NOR) are
the two central enzymes in this pathway. Here we present a previously
unreported Nir domain architecture in members of Phylum Chloroflexi.
Phylogenetic analyses of protein domains within Nir indicate that an
ancestral horizontal transfer and fusion event produced this chimeric
domain architecture. We also identify an expanded genomic diversity of a
rarely reported nitric oxide reductase subtype, eNOR. Together, these
results suggest a greater diversity of denitrification enzyme
arrangements exist than have been previously reported.