A hot origin of dissimilatory sulfite reduction catalyzed by DsrAB in the Palaeoarchean Era

Sulfur metabolism represents one of the most ancient and fundamental energy-acquiring strategies in early life evolution. In the anoxic waters of the early Earth, microorganisms carried out anaerobic respiration by reducing sulfate and sulfite, thereby driving the earliest biogeochemical sulfur cycle. The sulfide deposits from the Dresser Formation in Australia, reported by Shen et al. approximately 25 years ago, constitute the oldest isotopic geological evidence for dissimilatory sulfite reduction (DSR), placing the earliest DSR activity at least 3.47 billion years ago (Ga) in the Paleoarchean Era. Analyses based on multiple sulfur isotope systematics and crystal interfacial angles suggest these sulfides formed under mesothermal to moderate thermal environment, while more recent studies examining stromatolites, microbial fabrics, and bubble structures indicate that the Dresser Formation depositional environment may have been a terrestrial hydrothermal spring system.

The thermal conditions under which DSR originated thus remain unclear. Simultaneously, the genes encoding the key enzyme Dsr are subject to frequent horizontal gene transfer, which poses substantial technical challenges for evolutionary tracing and molecular dating and has left the field without reliable molecular clock estimates or independent temperature proxy evidence for DSR origins.

To address these gaps, the research team conducted a comprehensive evolutionary analysis of DsrAB, focusing on branches near the root of the phylogenetic tree and reconstructing the evolutionary trajectories of all key proteins in the Dsr cascade. The results show that the minimal functional cluster required for DSR, DsrABCNM, originated within a basal II clade predating the last common ancestor of reductive archaeal type DSR. Molecular dating places the origin of DSR at 3.51 Ga, in strong concordance with the oldest known geological DSR record (Figure 1). Through ancestral sequence reconstruction, the study predicts the optimal catalytic temperatures of ancestral DsrA proteins at successive evolutionary nodes. The node corresponding to the last common ancestor of functional DSR yields an optimal temperature of 73°C (Figure 1), providing independent molecular evolutionary evidence in support of a moderately thermophilic origin for DSR.

By integrating phylogenetics, molecular dating, and ancestral protein reconstruction, this study elucidates the molecular origins of DSR as a key metabolic innovation of early life, deepens our understanding of the coupling between gene origins and geological evolution, and offers a methodological reference for molecular evolutionary research into early life metabolism.

How to cite this article:

Tang L, Luo Z, Gao S, Lin Z, Sun M, Li R, et al. A hot origin of dissimilatory sulfite reduction catalyzed by DsrAB in the Paleoarchean Era. mLife. 2026;5:108-121. https://doi.org/10.1002/mlf2.70066