Novel insights into microbial DMSP/DMS cycling: from surface to deep ocean

The microbial cycling of dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS) constitutes a crucial component of the global sulfur cycle, influencing climate regulation through the release of climate-active gases. Since DMSP production has historically been attributed to planktonic algae, research on its cycling has consequently centered on the surface ocean. However, the continuous discovery of bacterial DMSP synthesis genes (dsyB, mmtN, and dsyGD) has confirmed that the DMSP/DMS cycling process may also exist in the aphotic deep-sea environment. Further supporting this, the recently identified hydrogen sulfide (H₂S)/methanethiol (MeSH)-dependent DMS-producing enzyme MddH, widespread among marine bacteria, may represent a significant source of DMS. This review integrates emerging insights into the ecological roles, environmental distribution, and microbial metabolism of these organic sulfur compounds, with a specific emphasis on deep-sea environments. We further discuss the distribution of key microbial taxa and functional genes involved in the biosynthesis and degradation of DMSP and DMS across deep-sea water columns and sediments. Collectively, this review highlights the existence of an active microbial DMSP/DMS cycling network in the deep ocean that remained overlooked until recently, with profound implications for global biogeochemical cycles and climate.