Phylogeny of Dissimilatory Sulfite Reductases Supports an Early Origin of Sulfate Respiration

TLDR

Sulfate‑reducing microorganisms are key players in the global sulfur cycle. The study compares DSR gene sequences across sulfate‑reducing organisms to reconstruct DSR evolutionary history. The authors performed comparative sequence analysis and PCR amplification of a 1.9‑kb DSR region from sulfate‑reducing organisms. DSR genes are highly conserved and phylogenetically congruent with 16S rRNA, indicating a single ancestral DSR predating or shortly after bacterial and archaeal divergence, implying early sulfate respiration.

Abstract

ABSTRACT Microorganisms that use sulfate as a terminal electron acceptor for anaerobic respiration play a central role in the global sulfur cycle. Here, we report the results of comparative sequence analysis of dissimilatory sulfite reductase (DSR) genes from closely and distantly related sulfate-reducing organisms to infer the evolutionary history of DSR. A 1.9-kb DNA region encoding most of the α and β subunits of DSR could be recovered only from organisms capable of dissimilatory sulfate reduction with a PCR primer set targeting highly conserved regions in these genes. All DNA sequences obtained were highly similar to one another (49 to 89% identity), and their inferred evolutionary relationships were nearly identical to those inferred on the basis of 16S rRNA. We conclude that the high similarity of bacterial and archaeal DSRs reflects their common origin from a conserved DSR. This ancestral DSR was either present before the split between the domains Bacteria , Archaea , and Eucarya or laterally transferred between Bacteria and Archaea soon after domain divergence. Thus, if the physiological role of the DSR was constant over time, then early ancestors of Bacteria and Archaea already possessed a key enzyme of sulfate and sulfite respiration.