Table6_Responses to organic pollutants in the tropical Pacific and subtropical Atlantic Oceans by pelagic marine bacteria.xlsx

Background and chronic pollution by organic pollutants (OPs) is a widespread threat in the oceans with still uncharacterized effects on marine ecosystems and the modulation of major biogeochemical cycles. The ecological impact and toxicity of this anthropogenic dissolved organic carbon (ADOC) is not related to the presence of a single compound but to the co-occurrence of a myriad of synthetic chemicals with largely unknown effects on heterotrophic microbial communities. We have analyzed the metabolic capacity of metagenome-assembled genomes (MAGs) of natural oceanic communities from the north Pacific (Costa Rica dome) and Atlantic oceans challenged with environmentally relevant levels of ADOC. In the Atlantic, ADOC-exposed MAGs responded transcriptionally more strongly compared to controls than in the Pacific, possibly mirroring the higher relevance of ADOC compounds as carbon source in oligotrophic environments. The largest proportions of transcripts originated from MAGs belonging in the families Rhodobacteraceae and Flavobacteriaceae, known to play a role on consumption of several OPs. In the Atlantic, archaeal Poseidoniales showed the highest transcription levels after 2 h of ADOC exposure, although no increase of relative abundances in the DNA pool was recorded after 24 h, whereas Methylophaga showed the opposite pattern. Both taxa are suggested to be actively involved in the consumption of biogenic alkanes produced by cyanobacteria. We observed similar gene expression profiles of alkane degradation and methylotrophy signature genes. These findings, plus the chemical degradation of alkanes measured in the experiments, provides experimental evidence of the consumption of anthropogenic hydrocarbons and synthetic chemicals at the low concentrations found in the ocean, and modulation of microbiomes by ADOC.

有机污染物（organic pollutants, OPs）引发的背景污染与长期污染是海洋中普遍存在的威胁，其对海洋生态系统及主要生物地球化学循环的调控效应尚未得到阐明。此类人为源溶解有机碳（anthropogenic dissolved organic carbon, ADOC）的生态影响与毒性并非源于单一化合物的存在，而是多种合成化学物质共同作用的结果，这类物质对异养微生物群落的影响大多尚不明确。
本研究分析了北太平洋（哥斯达黎加穹区）与大西洋天然海洋群落的宏基因组组装基因组（metagenome-assembled genomes, MAGs）的代谢能力，这些群落均暴露于环境相关浓度的ADOC中。与太平洋样本相比，大西洋中暴露于ADOC的MAGs的转录响应强度显著高于对照组，这或许反映了寡营养环境中ADOC作为碳源的重要性更高。
转录本占比最高的MAGs隶属于红杆菌科（Rhodobacteraceae）与黄杆菌科（Flavobacteriaceae），这两个类群已知可降解多种有机污染物。大西洋样本中，古菌类群波塞冬菌目（Poseidoniales）在ADOC暴露2小时后转录水平达到峰值，但24小时时DNA库中的相对丰度并未出现升高；而甲基噬胞菌属（Methylophaga）则呈现出相反的变化模式。上述两类群均被认为可主动参与降解蓝细菌产生的生物源烷烃。
本研究观测到烷烃降解基因与甲基营养特征基因的表达谱高度相似。结合实验中测得的烷烃化学降解数据，本研究的上述发现为海洋中低浓度人为源烃类与合成化学物质的降解利用，以及ADOC对海洋微生物组的调控作用提供了实验证据。