Bacterial transformations of dimethylsulfoniopropionate in the Weddell Sea

二甲基硫（DMS）是一种与气候相关的海洋来源的痕量气体，是大气中云凝结核的前体。南大洋被认为是二甲硫醚大量从海上转移到空中的区域。在南极大陆附近和季节性海冰融化区发现了二甲基硫醚生产的热点。模式模拟表明，海洋-大气DMS通量的扰动可以改变云的覆盖范围，从而可能影响大气辐射平衡。因此，了解和预测海洋二甲硫醚的产生对于未来的气候变化情景至关重要。二甲硫醚是由植物甾醇衍生的二甲基磺基丙酸酯（DMSP）在海洋表层细菌降解而产生的。细菌DMSP降解通过两个竞争的酶介导的途径发生：去甲基化途径和裂解途径。由于只有裂解途径导致二甲硫醚的产生，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二甲硫醚从海洋向大气的通量的调节非常重要。30多年前人们就认识到海洋DMSP循环在全球范围内的影响，但直到最近才开发出分子生物学方法和生物组学方法，确定了参与细菌DMSP代谢的基因，并深入了解了它们的系统发育分布。迄今为止，我们对DMSP循环的了解主要来自在低纬度和中纬度进行的研究，而对极地海洋的了解非常有限。在威德尔海的细菌群落组成的分析，通过16 S rRNA扩增子测序揭示了高丰度的潜在DMS生产的细菌群，如玫瑰花分支和SAR 11。在拟议的项目中，我们希望将分子生物学中最先进的方法与生物信息学工具相结合，以（1） 分析细菌降解DMSP的环境规律（2） 研究DMSP降解菌的多样性和分类;（3） 分析DMSP转化的基因库，以及（4） 描述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、菲尔希纳-罗恩冰架和威德尔环流沿着收集的海水样本进行分析。预期的结果将提高在威德尔海的细菌DMSP降解的机制的理解，并有助于在未来的气候情景下，在南大洋的海洋二甲基硫醚排放的可靠预测。

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.