Dissolved Organic Carbon Cycling by SAR11 Marine Bacteria

SAR11是海洋中数量最多的浮游细菌类群。在全球范围内，据估计，它们每天氧化成二氧化碳(CO2)的有机碳占光合作用产生的所有有机碳的5%到22%。浮游细菌的活动，如SAR11，决定了不同形式有机碳的停留时间，并最终塑造了海洋中溶解有机池的组成，在质量上与大气中的二氧化碳相媲美。关于海洋碳循环的准确而详细的信息被用于模型，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。这笔赠款支持对预测SAR11细胞碳氧化功能的基因组数据的分析，并支持用培养中的细胞进行实验，在培养中应用高分辨率质谱仪技术来发现新的有机碳氧化生物化学。为评估SAR11碳氧化功能在海洋生态系统中的重要性，该项目包括前往西部马尾藻海的百慕大大西洋时间序列研究(BATS)地点的四次短途海洋游轮。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SAR11种群的变化联系起来。这笔赠款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。这个项目帮助来自农村地区的少数民族、低收入、历史上受教育程度较低的学生和其他受教育程度较低的学生高中毕业，接受高等教育并取得成功，追求科学、技术、工程或数学事业。SAR11细胞是海洋中最丰富的细胞，但也拥有已知的最小基因组，这是一个悖论。该提案的中心目标是了解SAR11将哪些类型的溶解有机物(DOM)氧化为二氧化碳。这种方法隐含的观点是，一些丰富的化学异养浮游细菌分类群，特别是那些具有小基因组的类群，已经进化出氧化有机物的专门策略。了解这些策略可以更详细、更准确地了解将生物生产循环为二氧化碳的生物过程。项目的主要目标是：1)利用高分辨率质谱仪和同位素标记法调查SAR11基因组和培养细胞，以确定这些细胞可以氧化成二氧化碳的化合物的范围；2)在BATS，测量SAR11使用的DOM化合物的生物氧化率；3)将SAR11基因组的时空变化与海洋表层(0-300米)DOM氧化模式联系起来。该项目包括四次前往BATS的短途游轮，目标是该地点的四种浮游生物群落类型：上层真光带、深层叶绿素最大值、春季水华和上层中层浮游生物。这项活动的产品将包括关于表层不稳定的DOM氧化变化的新信息，以及与基因组特征的具体联系，这将提高对全球海洋元基因组数据的解释的准确性。

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.