Dissolved Organic Carbon Cycling by SAR11 Marine Bacteria

SAR11 （Pelagibacterales）是海洋中最丰富的浮游细菌群。在全球范围内，据估计，它们每天被氧化为二氧化碳（CO2），占光合作用产生的所有有机碳的5%至22%。浮游细菌（如SAR11）的活动决定了不同形式有机碳的停留时间，并最终形成了海洋中溶解有机池的组成，其质量可与大气中的二氧化碳相媲美。关于海洋碳循环的准确和详细信息被用于模型中，这些模型因其预测和了解海洋生态系统未来变化的潜力而受到重视。该基金支持预测SAR11细胞碳氧化功能的基因组数据分析，并支持培养细胞实验，其中高分辨率质谱技术应用于发现新的有机碳氧化生物化学。为了评估SAR11碳氧化功能在海洋生态系统中的重要性，该项目包括对位于马尾藻海西部的百慕大大西洋时间序列研究（BATS）站点进行四次短途海洋考察。在这些巡航中，将测量有机化合物的浓度和氧化速率，并将其与浮游生物SAR11种群的变化联系起来。该基金还支持俄勒冈州立大学科学与数学研究性学习经验（SMILE）项目中关于海洋微生物碳循环主题的教师专业发展培训。该项目帮助来自农村地区的少数民族、低收入、历史上代表性不足和其他教育服务不足的学生从高中毕业，进入高等教育并取得成功，并从事科学、技术、工程或数学职业。SAR11细胞是海洋中最丰富的，但也是已知最小的基因组之一，这是一个悖论。本提案的中心目标是了解哪些类型的溶解有机物（DOM）被SAR11氧化为CO2。这种方法隐含的观点是，一些丰富的化学异养细菌浮游生物分类群，特别是那些基因组小的细菌，已经进化出了氧化有机物的专门策略。了解这些策略可以更详细和准确地了解将生物生产转化为二氧化碳的生物过程。主要项目目标是：1)研究SAR11基因组，并利用高分辨率质谱方法和同位素标记技术检测培养细胞，以确定这些细胞可以氧化为CO2的化合物范围；2)在BATS，测定SAR11使用的DOM化合物的生物氧化速率；3)将SAR11基因组的时空变异与海洋表层（0-300 m） DOM氧化模式联系起来。该项目包括四次对BATS的短途巡航，目标是该站点的四种浮游微生物群落类型：上光带、深叶绿素最大值、春季开花和中上层。这项活动的成果将包括关于表层不稳定DOM氧化变化的新信息，以及与基因组特征的具体联系，这将提高全球海洋宏基因组数据解释的准确性。

SAR11 (Pelagibacterales) are the most abundant group of bacterioplankton in the oceans. Globally, they are estimated to oxidize to carbon dioxide (CO2) between 5 and 22% of all the organic carbon produced by photosynthesis each day. The activities of bacterioplankton such as SAR11 determine the residence times of different forms of organic carbon, and ultimately shape the composition of dissolved organic pools in the oceans, which rival atmospheric CO2 in mass. Accurate and detailed information about the oceanic carbon cycle is used in models that are valued for their potential to predict and understand future changes in ocean ecosystems. This grant supports analyses of genomic data that predict the carbon oxidation functions of SAR11 cells, and supports experiments with cells in culture, where high-resolution mass spectrometry technology is applied to discover new organic carbon oxidation biochemistry. To assess the importance of SAR11 carbon oxidation functions in ocean ecosystems, this project includes four short oceanographic cruises to the Bermuda Atlantic Time-series Study (BATS) site, in the western Sargasso Sea. On these cruises the concentrations and oxidation rates of organic compounds will be measured, and linked to variation in planktonic SAR11 populations. This grant also supports teacher professional development training on the topic of Carbon Cycling by Marine Microorganisms, in Oregon State University's Science & Math Investigative Learning Experiences (SMILE) program. This program prepares minority, low-income, historically underrepresented, and other educationally underserved students from rural areas to graduate from high school, enroll and succeed in higher education, and pursue science, technology, engineering or mathematics careers.It is a paradox that SAR11 cells are the most abundant in the oceans, but also have among the smallest genomes known. The central goal of this proposal is to understand what types of dissolved organic matter (DOM) are oxidized to CO2 by SAR11. Implicit to this approach is the perspective that some abundant chemoheterotrophic bacterioplankton taxa, particularly those with small genomes, have evolved specialist strategies for oxidizing organic matter. Understanding these strategies can lead to a more detailed and accurate understanding of the biological processes that recycle biological production to CO2. Major project aims are: 1) investigate SAR11 genomes and assay cells in culture with high-resolution mass spectrometry approaches and isotopic labeling to identify the range of compounds these cells can oxidize to CO2; 2) at BATS, measure biological oxidation rates of DOM compounds used by SAR11; 3) link spatiotemporal SAR11 genome variation to patterns of DOM oxidation in the ocean surface layer (0-300 m). This projects includes four short cruises to BATS that target the four microbial plankton community types at this site: upper euphotic zone, deep chlorophyll maximum, spring bloom and upper mesopelagic. Products of this activity will include new information about variation in labile DOM oxidation across the surface layer, and specific links to genome features that will improve the accuracy of interpretation of global ocean metagenomic data.