Microbial sulfur metabolism plays a critical role in the transformation of organic carbon compounds and nutrients in the environment, human health and disease, and drives key planetary biogeochemical cycles. Our current knowledge of the microbial ecology associated with this key element is primarily based on single gene- and cultivation-based studies that provide no reliable information on comprehensive microbial metabolism and paint a biased picture of microbial community composition. Genome-resolved metagenomics, an approach that can yield near-complete and even finished genomes for organisms, has the potential to fundamentally transform our understanding of ecosystems by enabling organism-specific descriptions of elemental transformations and redox processes.
In this presentation, I will describe the metabolic analysis of >4000 near-complete and complete microbial and >10,000 viral genomes to implicate new players in sulfur cycling. The genes identified include those encoding for dissimilatory sulfite reductases (for the reduction of sulfite to sulfide), reverse-dissimilatory sulfite reductases (for the oxidation of sulfur to sulfite), anaerobic sulfite reductases (for the reduction of sulfite to sulfide), and the sox enzyme complex (for the oxidation of thiosulfate). Amongst the organisms identified are those from eight candidate phyla, and two of these lineages contain dissimilatory sulfite reductase sequences that are deduced to be amongst the most ancient. These findings fundamentally reshape our understanding of the biogeochemical cycle of sulfur.