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Dimethyl sulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) are ubiquitous sulfur compounds in the ocean. DMS is emitted into the atmosphere and has potential climatic effects. The distributions of DMS and DMSP are affected by various biological factors (i.e., bacterial catabolism and phytoplankton and zooplankton community composition). The horizontal and vertical distributions of DMSP, DMSP lyase activity (DLA), DMS, and the abundances of bacteria, DMSP‐consuming bacteria, dimethyl sulfoxide‐consuming bacteria, and picophytoplankton were investigated in the Bohai Sea (BS) and Yellow Sea (YS) during autumn 2020. DLA was significantly correlated with chlorophyll a, DMS, and dissolved DMSP concentrations. Our data show that bacteria Clade_I SAR11 was a significant contributor to DLA. A dilution experiment indicated that the highest microzooplankton grazing rate coincided with the highest DMS concentration and DMS production rate. A proportion of 16%–62% of the DMSPt was converted to DMS in the dilution experiment. Copepods dominated the mesozooplankton community. Calanus sinicus was the predominant copepod in the BS and YS. C. sinicus grazing stimulated DMS production. DMS concentration increased 299% after C. sinicus grazing on physically broken algal cells for 48 hr. These results will help with a better understanding of the control of DMS and DMSP concentrations by zooplankton and the DMS release mechanisms that occur through zooplankton grazing. Plain Language Summary: Dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS) are transferred and transformed in the food web and are affected by zooplankton, phytoplankton, and bacteria. This study investigated spatial distributions of DMS, DMSP, DMSP lyase activity (DLA), the abundances of bacteria, DMSP‐consuming bacteria, and dimethyl sulfoxide‐consuming bacteria in the surface seawater of the Bohai Sea and Yellow Sea. As results, the distributions of DMS and dissolved DMSP were significantly correlated with DLA. A deck incubation experiment indicated that grazing by microzooplankton promoted the conversion of DMSP to DMS and that mesozooplankton copepod grazing stimulated DMS production. These results provide a more comprehensive way to understand the possible DMS release mechanisms via zooplankton grazing. Key Points: Dimethyl sulfide (DMS) concentration was significantly correlated with dimethyl sulfoxide‐consuming bacterial abundanceMicrozooplankton grazing consumed 4%–7% of the total dimethylsulfoniopropionate daily and 16%–62% was converted to DMSCopepod ingestion stimulated DMS production, which increased by 299% at 48 hr in physically broken algal cells [ABSTRACT FROM AUTHOR]

The fate of dimethylsulfoniopropionate (DMSP), the precursor of the climatologically important gas dimethylsulfide (DMS), depends on the structure of marine communities. DMSP degradation by DMSP‐consuming bacteria (DCB) is an important sink of dissolved DMSP (DMSPd) in seawater. DMSP cleavage and demethylation are two DMSPd consumption pathways, and the DMSPd cleavage pathway involves DMSP lyase activity (DLA). Here, we studied the distribution of DMS, DMSP, DCB, and DLA in the seawater of the Yellow Sea and East China Sea in the summer of 2013 and the degradation of DMSPd by DCB. High DCB abundances, as well as DMS and dissolved, particulate, total DMSP (DMSPd,p,t) concentrations were observed near the Hongzhou Bay, which may be due to the high productivity of dinoflagellates. The spatial distribution of DCB abundance was most likely the result of the regional hydrography including upwelling near Hangzhou Bay and the discharge of Yangtze Diluted Water (YDW). The DLA along the YDW decreased from coastal water to open sea. The DMSPd consumption by DCB Bacillus sp. YES023 isolated from the seawater was accompanied by DMS production (≤8.2% of DMSPd consumption). Bacillus sp. YES023 could also grow using glycine betaine, acrylic acid, dimethylsulfoxide, monomethylamine, or dimethylamine as a sole carbon source. Glycine betaine and acrylic acid were the most favorable substrates for overall growth. These results help our understanding of bacterial catabolism and the degradation pathways of methyl sulfur compounds in the ocean. Plain Language Summary: Bacterial catabolism of dissolved dimethylsulfoniopropionate (DMSP) (DMSPd) is an important sink of DMSP in seawater. There are two DMSPd consumption pathways (DMSP cleavage and demethylation), and the dimethylsulfide (DMS)‐producing (DMSP cleavage) pathway involves DMSP lyase activity (DLA). In this study, we evaluated the DMS, DMSP, DMSP‐consuming bacteria (DCB) abundance, and DLA distributions in the seawater of the Yellow Sea and East China Sea. DCB in the seawater were isolated and identified. The degradation of DMSPd by and the bioavailability of the other five organic carbon analog of DMSP (including glycine betaine, acrylic acid, dimethylsulfoxide, monomethylamine, and dimethylamine) to DCB Bacillus sp. YES023 were investigated. Key Points: Dimethylsulfoniopropionate (DMSP)‐consuming bacteria abundance and DMSP lyase activity were evaluatedDMSP consumption by Bacillus sp. YES023 was accompanied by dimethylsulfide production (≤8.2%)Glycine betaine and acrylic acid were more favorable as substrates for the growth of Bacillus sp. YES023 than DMSP [ABSTRACT FROM AUTHOR]