Elucidation of dimethyl sulfide assimilation in soil bacteria expands the enzymatic landscape of terrestrial sulfur cycling.

Abstract

Dimethyl sulfide (DMS) is a central volatile sulfur intermediate in the global sulfur cycle, traditionally associated with marine ecosystems. However, despite significant advances, important gaps remain in our understanding of its metabolism in terrestrial environments. Here, we elucidate a complete DMS catabolic pathway for sulfur utilization in the soil bacterium Acinetobacter baylyi ADP1 using an integrative approach combining targeted metabolomics, genetic knockouts, and in vitro enzyme assays. The pathway consists of a series of oxidation reactions catalyzed by two-component monooxygenases, including newly identified enzymes responsible for the sequential conversion of DMS to dimethyl sulfoxide and then dimethyl sulfone. These steps are followed by previously reported downstream enzymes that form methanesulfinate and methanesulfonate, ultimately yielding sulfite for cysteine biosynthesis. Functional redundancy and substrate promiscuity characterize these monooxygenases, all of which are powered by a single flavin reductase. A genomic survey revealed that this pathway is widespread among plant-associated and soil-dwelling Proteobacteria, including Pseudomonas putida and Rhodococcus opacus, which were experimentally confirmed to grow on DMS. Our findings reveal a widespread terrestrial DMS metabolic route that may represent a significant, yet previously unrecognized, component of the global sulfur cycle.