Timing the evolution of the dissimilatory sulfur cycle: a bridge between genes and geochemistry

Earth's biogeochemical sulfur cycle is driven by various microbial dissimilatory processes that couple sulfur redox transformations with energy conservation.

These dissimilatory sulfur metabolisms are catalysed by a linked suite of ""enzymatic machineries"" composed largely of multimeric protein complexes.

Over geological timescales, the sulfur-cycling ""machineries"" have co-opted to create a dissimilatory metabolic network at planetary scale, which has had tremendous consequences on the Earths major biogeochemical cycles, surface redox states and climate stability.

The advent and expansion of sulfur-cycling ""machineries"" thus represent milestones in the multibillion-year history of Earth and life.

Yet, the timing of the onset of diverse dissimilatory sulfur metabolisms and their interplay with sulfur geochemistry remain generally unconstrained due to the rarity of microbial fossils and ambiguity of ancient stable isotope signatures.

The research proposed herein will explore the origin and evolution of dissimilatory sulfur metabolisms by leveraging genomes of uncultivated bacteria and archaea from metagenomes, advances in molecular clock and quantitative evolutionary models, and extensive compilations of sedimentary sulfur isotope records.

A novel combination of large-scale comparative phylogenetic analyses and geochemical data will (1) derive expanded phylogenies for a comprehensive set of genes encoding full repertoires of dissimilatory metabolisms of inorganic and organic sulfur compounds, including uncharted sequences from new genomes; (2) map the evolutionary history of sulfur-cycling genes onto a geological timeline; and (3) formulate testable hypotheses on feedbacks between historical shifts in sulfur geochemistry and metabolic innovations.

The aim of this work is to create the first unified timescale for the evolution of dissimilatory sulfur metabolisms and geochemistry, and document the transitions of early Earths sulfur cycle towards its modern complexity.