Bacterial transformations of dimethylsulfoniopropionate in the Weddell Sea

二甲基硫化物（DMS）是一种与气候有关的海洋微量气体，是大气中云凝结核的前体。南大洋是公认的DMS海空转移的重要区域。DMS的生产热点靠近南极大陆和季节性海冰融化区。模式模拟表明，海洋-大气DMS通量的扰动可以改变云覆盖，从而可能影响大气辐射平衡。因此，了解和预测海洋DMS产量对未来气候变化情景至关重要。DMS是由细菌降解浮游植物衍生的二甲基磺酰丙酸（DMSP）在海洋表面产生的。细菌DMSP降解通过两种相互竞争的酶介导途径发生：去甲基化途径和裂解途径。由于只有裂解途径导致DMS的产生，因此更好地了解控制这两种途径之间平衡的环境因素和遗传能力对于评估生物驱动的从海洋到大气的DMS通量的调节具有重要意义。虽然海洋DMSP循环在全球范围内的意义已经被认识了30多年，但直到最近才发展出分子生物学和“组学”方法，确定了参与细菌DMSP代谢的基因，并提供了对其系统发育分布的见解。迄今为止，我们对DMSP循环的了解主要来自低纬度和中纬度地区的研究，而对极地海洋的了解非常有限。通过16S rRNA扩增子测序对威德尔海细菌群落组成进行分析，发现大量可能产生dms的细菌群，如Roseobacter分支和SAR11。在该项目中，我们希望应用分子生物学的最新方法结合生物信息学工具来(1)分析细菌DMSP降解的环境调控(2)研究DMSP降解细菌的多样性和分类，(3)分析DMSP转化的基因清单，(4)表征威德尔海关键物种的代谢和生态策略。将对沿东威德尔海冰架、费尔奇纳-罗纳冰架和威德尔环流收集的海水样本进行分析。预期结果将提高对威德尔海细菌DMSP降解机制的理解，并有助于在未来气候情景下可靠地预测南大洋海洋DMS排放。

Dimethylsulfide (DMS) is a climate-relevant trace gas of marine origin that acts as a precursor of cloud condensation nuclei in the atmosphere. The Southern Ocean is recognized as a region of significant sea-to-air transfer of DMS. Hotspots of DMS production were detected close to the Antarctic continent and in the zone of seasonal sea ice melting. Model simulations revealed that the perturbation of ocean-atmosphere DMS fluxes can alter the cloud coverage and, thereby, potentially affect the atmospheric radiative balance. Consequently, understanding and predicting marine DMS production is critical to future climate change scenarios. DMS is produced in the surface ocean by the bacterial degradation of phytoplankton-derived dimethylsulfoniopropionate (DMSP). Bacterial DMSP degradation occurrs via two competing, enzymatically mediated pathways: the demethylation pathway and the cleavage pathway. Since only the cleavage pathway results in the production of DMS, a better understanding of environmental factors and genetic capabilities that control the balance between the two pathways is of high importance to assess the regulation of biologically driven DMS fluxes from the ocean to the atmosphere. While global-scale implications of marine DMSP cycling had been recognized for more than 30 years, only recently developed methods in molecular biology and ‟omics” approaches identified genes involved in the bacterial DMSP metabolism and provided insight into their phylogenetic distribution. To date, our understanding of DMSP cycling is largely derived from studies conducted at low- and mid-latitudes, while the knowledge on polar oceans is very limited. The analysis of the bacterial community composition in the Weddell Sea by means of 16S rRNA amplicon sequencing revealed high abundances of potentially DMS-producing bacterial groups like the Roseobacter clade und SAR11. In the proposed project, we want to apply state-of-the-art methods in molecular biology combined with bioinformatics tools to(1) analyse the environmental regulation of bacterial DMSP degradation (2) investigate the diversity and taxonomy of DMSP-degrading bacteria,(3) analyse the gene inventory for DMSP transformations and(4) characterize metabolic and ecological strategies of keystone species in the Weddell Sea. Seawater samples collected along the Eastern Weddell Sea ice shelf, the Filchner-Ronne ice shelf and in the Weddell Gyre will be analyzed. Expected results will improve the mechanistic understanding of bacterial DMSP degradation in the Weddell Sea and contribute to reliable projections of marine DMS emissions in the Southern Ocean under future climate scenarios.