Microbially Driven Sulfur Cycling in the River–Wetland–Ocean Continuum

Sulfur (S) is an essential biological element, and S cycling is mainly driven by metabolically versatile microorganisms. The river–wetland–ocean (RWO) continuum here is defined as the dynamically connected region with estuary, wetland, and near-marine ecosystems, and it is considered a hotspot of biogeochemical cycling, especially a major biotope for S cycling. Various forms and oxidation states of S compounds are considered ideal electron donors or acceptors and are widely utilized by microorganisms via inorganic or organic S-cycling processes. The S-cycling pathways are intimately linked to the carbon (C), nitrogen, phosphorus, and metal cycles, playing crucial roles in biogeochemical cycling, C sequestration, and greenhouse gas emissions through various mechanisms in the RWO continuum. This review provides a comprehensive understanding of microbially driven S cycling in the RWO continuum. We first illustrate the importance of S cycling in this continuum, including key microorganisms and functional processes (e.g., dissimilatory sulfate reduction, S oxidation, dimethylsulfoniopropionate production, and catabolism) as well as their corresponding S flux characteristics. In particular, we emphasize recent advances in the coupling mechanisms of the S cycle with other major element cycles. We further propose important perspectives for developing microbiome engineering of S-cycling microbial communities via integration of current knowledge about the multidimensional diversity, cultivation, evolution, and interaction of S-cycling microorganisms and their coupling mechanisms in the RWO continuum, providing a new window on applying microbiome-based biotechnologies to overcome global climate challenges.