Vertical distributions of dimethyl sulfide and dimethylsulfoniopropionate and impacts of DMSP lyase and bacteria in the Yellow Sea and East China Sea.

Dimethyl sulfide (DMS), a degradation product of dimethylsulfoniopropionate (DMSP), is a significant trace gas influencing global temperature. This study examined the distribution of DMSP lyase activity (DLA) and the degradation of DMSP and dimethyl sulfoxide (DMSO) by bacteria to elucidate the influences of DMSP lyase and bacteria on the distributions of DMS and DMSP in the Yellow Sea and the East China Sea during the summer. We observed that DMS and DMSP concentrations in transect B, located near the Yellow Sea Cold Water Mass, declined with deepening water depth, coinciding with the changing trend of the temperatures. A positive correlation between Chl a and dissolved and particulate dimethylsulfoniopropionate (DMSP) concentrations in transects B, D, F, P, and T indicated that DMSP primarily originated from phytoplankton. The phytoplankton in transects D, F, and P thrived under the nutrient-rich conditions brought by the Yangtze Diluted Water. A positive correlation between DMS concentrations and DMSP concentrations was found, suggesting that DMS originated from the degradation of DMSP. Additionally, we successfully isolated twenty-one DMSP-degrading bacteria and twelve DMSO-degrading bacteria capable of utilizing DMSP or DMSO as their sole carbon and sulfur sources. DMSP was consumed by DMSP-degrading bacteria, which simultaneously transformed it into DMS. The DMS production pathway accounted for 2.5%-47.1% of the total DMSP degradation process. Furthermore, the addition of glucose enhanced DMSO degradation by DMSO-degrading bacteria by a factor of 4.5-7.0 compared to conditions without glucose. These findings advance our understanding of the key factors influencing DMS and DMSP dynamics, as well as the roles of DMSP lyase and bacteria in the organic sulfur cycle.