The rapid turnover of dimethylsulfoniopropionate (DMSP), likely the most relevant dissolved organic sulfur compound in the surface ocean, makes it pivotal to understand the cycling of organic sulfur. Dimethylsulfoniopropionate is mainly synthesized by phytoplankton, and it can be utilized as carbon and sulfur sources by marine bacteria or cleaved by bacteria or algae to produce the volatile compound dimethylsulfide (DMS), involved in the formation of sulfate aerosols. The fluxes between the consumption (i.e., demethylation) and cleavage pathways are thought to depend on community interactions and their sulfur demand. However, a quantitative assessment of the sulfur partitioning between each of these pathways is still missing. Here, we report for the first time the sulfur isotope fractionations by enzymes involved in DMSP degradation with different catalytic mechanisms, expressed heterologously in Escherichia coli. We show that the residual DMSP from the demethylation pathway is 2.7‰ enriched in δ ³⁴S relative to the initial DMSP, and that the fractionation factor (³⁴ε) of the cleavage pathways varies between −1 and −9‰. The incorporation of these fractionation factors into mass balance calculations constrains the biological fates of DMSP in seawater, supports the notion that demethylation dominates over cleavage in marine environments, and could be used as a proxy for the dominant pathways of degradation of DMSP by marine microbial communities.

中文翻译：

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硫同位素分馏限制了上层海洋中二甲基磺基丙酸盐的生物循环

二甲基磺基丙酸酯 (DMSP) 可能是表层海洋中最相关的溶解有机硫化合物，其快速转换使得了解有机硫的循环变得至关重要。二甲基磺基丙酸盐主要由浮游植物合成，可被海洋细菌作为碳源和硫源利用，或被细菌或藻类裂解产生挥发性化合物二甲硫醚（DMS），参与硫酸盐气溶胶的形成。消耗（即去甲基化）和裂解途径之间的通量被认为取决于群落相互作用及其硫需求。然而，仍然缺少对这些途径中的每一个之间的硫分配的定量评估。这里，大肠杆菌。我们表明，相对于初始 DMSP，来自去甲基化途径的残余 DMSP 富含 2.7‰ 的δ ³⁴ S，并且裂解途径的分馏因子 ( ³⁴ ε ) 在 -1 和 -9‰ 之间变化。将这些分馏因子纳入质量平衡计算，限制了海水中 DMSP 的生物命运，支持去甲基化在海洋环境中占主导地位的观点，并可用作海洋微生物群落降解 DMSP 的主要途径的代表.