Table_1_Abundance and Diversity of Dimethylsulfoniopropionate Degradation Genes of Roseobacter Group in the Northern South China Sea.docx

Bacterial degradation of dimethylsulfoniopropionate (DMSP) plays a significant role in ecosystem productivity and global climate. In this study, the abundance and diversity of Roseobacter group DMSP degradation genes were explored in spatial scale of the South China Sea (SCS). Quantitative PCR showed that a higher abundance of dmdA (DMSP demethylase) and dddP (DMSP lyase) genes was detected above 75 m than deep water, especially in surface water. A high ratio of dmdA/dddP existed in all sites and increased with water depth, indicating that demethylation was the main degradation pathway in the Roseobacter group. High-throughput sequencing analysis showed that distribution of dmdA gene had a significant layering structure in the northern SCS, and high taxonomic diversity of dmdA gene was observed in near-surface waters (25 and 50 m). DmdA gene in the Roseobacter group, such as Leisingera, Nioella, Roseobacter, Roseovarius, Donghicola, Phaeobacter, and Tateyamaria, had remarkable specificity due to the effect of different sites and water depths. Different ecological strategies of DMSP degradation may be used by members of the bacterial community harboring demethylation genes. In addition, many dmdA sequences were affiliated with unidentified bacteria, indicating that the SCS reserved high diversity of DMSP-degrading bacteria. Canonical correspondence analysis (CCA) suggested that temperature and depth were the most important factors to determine the taxonomic distribution of DMSP degradation genes in the Roseobacter group, as well as their abundance. This study highlighted the understanding of the role of Roseobacter group in DMSP degradation in the tropical ocean.

二甲基硫代丙酸盐（DMSP）的细菌降解在生态系统生产力和全球气候中发挥着重要作用。本研究探讨了南海（SCS）空间尺度下Roseobacter菌群DMSP降解基因的丰度和多样性。定量PCR结果显示，在75米以上的水层中检测到的dmdA（DMSP去甲基化酶）和dddP（DMSP裂解酶）基因的丰度高于深层水，尤其是在表层水中。所有站点均存在dmdA/dddP的高比例，且随着水深增加而升高，表明去甲基化是Roseobacter菌群的主要降解途径。高通量测序分析显示，dmdA基因在南海北部存在显著的层状结构，且在近表层水（25米和50米）中观察到高分类多样性。由于不同地点和水深的影响，Roseobacter菌群中的DmdA基因，如Leisingera、Nioella、Roseobacter、Roseovarius、Donghicola、Phaeobacter和Tateyamaria等，具有显著的特异性。携带去甲基化基因的细菌群落可能采用不同的DMSP降解生态策略。此外，许多dmdA序列与未知的细菌相关联，表明南海保留了高多样性的DMSP降解细菌。典范对应分析（CCA）表明，温度和深度是决定Roseobacter菌群中DMSP降解基因的分类分布及其丰度的最重要的因素。本研究突出了在热带海洋中理解Roseobacter菌群在DMSP降解中的作用。