Table_1_Enrichment of Bacterioplankton Able to Utilize One-Carbon and Methylated Compounds in the Coastal Pacific Ocean.docx

Understanding the temporal variations and succession of bacterial communities involved in the turnover of one-carbon and methylated compounds is necessary to better predict bacterial impacts on the marine carbon cycle and air-sea carbon fluxes. The ability of the local bacterioplankton community to exploit one-carbon and methylated compounds as main source of bioavailable carbon during a productive and less productive period was assessed through enrichment experiments. Surface seawater was amended with methanol and trimethylamine-N-oxide (TMAO), and bacterial abundance, production, oxygen consumption, as well as methanol turnover and growth rates of putative methylotrophs were followed. Bacterial community structure and functional diversity was examined through amplicon sequencing of 16S rRNA and methanol dehydrogenase (mxaF) marker genes. 2-fold increase in oxygen consumption and bacterial growth rates, and up to 4-fold higher methanol assimilation were observed in the amended seawater samples. Capacity to drawdown the substrates was similar between both experiments. In less productive conditions, methanol enriched obligate methylotrophs, especially Methylophaga spp., accounted for ∼70% of bacterial cells analyzed by fluorescence in situ hybridization and 16S rRNA gene sequencing, while TMAO enriched taxa belonged to Oceanospirillales and putative β- and γ-Proteobacterial methylotrophs. In the experiment performed during the more productive period, bacterial communities were structurally resistant, suggesting that facultative organisms may have dominated the observed methylotrophic activity. Moreover, enrichment of distinct methylotrophic taxa but similar activity rates observed in response to different substrate additions suggests a functional redundancy of substrate specific marine methylotrophic populations. Marine bacterioplankton cycling of one-carbon and methylated compounds appears to depend on the system productivity, and hence may have predictable temporal impacts on air-sea fluxes of volatile organic compounds.

解析参与一碳及甲基化化合物周转的细菌群落的时间动态与演替规律，有助于更精准地预测细菌对海洋碳循环及海-气碳通量的影响。本研究通过富集培养实验，评估了在高生产力与低生产力周期中，本地浮游细菌群落利用一碳及甲基化化合物作为主要生物可利用碳源的能力。向表层海水添加甲醇与氧化三甲胺（trimethylamine-N-oxide, TMAO）后，本研究追踪了细菌丰度、细菌生产力、耗氧速率，以及潜在甲基营养菌（methylotrophs）的甲醇周转速率与生长速率。通过对16S核糖体RNA（16S rRNA）与甲醇脱氢酶（methanol dehydrogenase, mxaF）标记基因的扩增子测序，分析了细菌群落结构与功能多样性。结果显示，添加底物的海水样本中，耗氧速率与细菌生长速率提升2倍，甲醇同化速率最高可达4倍。两组实验的底物消耗能力相近。在低生产力条件下，甲醇富集的专性甲基营养菌（obligate methylotrophs）——尤其是噬甲基菌属（Methylophaga spp.）——在经荧光原位杂交（fluorescence in situ hybridization）与16S rRNA基因测序分析的细菌细胞中占比约70%；而氧化三甲胺富集的类群则隶属于海洋螺菌目（Oceanospirillales）及潜在的β-、γ-变形菌门甲基营养菌。在高生产力周期开展的实验中，细菌群落结构表现出抗性，这表明兼性营养生物可能主导了观测到的甲基营养活性。此外，针对不同底物添加的响应中，虽富集了不同的甲基营养类群，但活性速率相近，这表明海洋中底物特异性的甲基营养种群存在功能冗余现象。海洋浮游细菌对一碳及甲基化化合物的周转过程似乎依赖于系统生产力，因此其对海-气挥发性有机化合物通量的影响具备可预测的时间动态特征。