Microbial cycling of volatile organic carbon in the marine surface layer

在浮游细菌基因组中盛行的挥发性有机化合物代谢的特殊基因是一把“确凿证据”，表明潜在的VOC循环具有重大意义。俄勒冈州立大学和科罗拉多大学博尔德分校的研究人员将通过以下方式收集有关海洋光层VOC循环的新证据：1)测量表层海洋低层大气(SOLAS)巡航中浮游生物群落的VOC化合物周转率；2)确定调节VOC氧化的生物和生化机械。这项研究具有潜在的变革性，因为表明显著的VOC循环的定量证据将导致碳循环模型的彻底改革，并将注意力集中在专门的代谢过程上，这些过程很少受到关注，也没有得到很好的描述。由于类似的原因，这项研究的风险很高：虽然越来越多的证据表明存在一个重要的“隐藏碳循环”，但其重要性只有在其规模被测量后才能知道，而实现这一目标需要对专业知识和技术进行投资。该项目是大气化学家和海洋微生物学家的合作项目，他们汇集了在SOLAS巡航和实验室环境中解决这一问题所需的知识和技术。通过测量海水中挥发性有机化合物(如甲醇、甲醛、二甲基硫化物、三甲胺、三甲胺、乙腈、丙酮、异戊二烯、乙二醛、甲基乙二醛和乙醛)的浓度以及通过同位素标记化合物与微生物浮游生物悬浮液孵化而确定的周转率，将提供有关这些地球化学过程在从多产大陆架延伸到低营养亚热带环流的断面上变化的信息。稍后，同一团队将在受控环境下测量微生物分离株对这些化合物的产生和氧化，重点放在氧化VOC(OVOC)和甲基化溶解有机碳(MDOC)氧化一个碳(C1)单位的生化途径上。对野外微生物多样性和实验室转录组反应的全面测量将为未来将VOC循环与特定生物体、代谢途径和基因联系起来的研究奠定基础，并了解微生物群落何时参与这些过程以及对什么选择压力做出反应。广泛的影响：VOCs在大气化学中扮演着不同而重要的角色，充当臭氧和气溶胶的光化学形成的前体，这两种二次污染物也影响气候的辐射强迫。关于海洋表面挥发性有机碳生物来源和汇的信息可能有助于更好地了解大气/海洋挥发性有机化合物通量变化的根本原因，并有可能改变对气候变化对海洋表面生态和海气相互作用的影响的预测。此外，该项目将解决挥发性有机碳循环背后的生化机制，并应提供相关基因功能的实验证据。因此，这项工作产生的修订的基因注释可以提高根据基因组和元基因组对未来VOC代谢的预测的准确性。该计划包括对博士后、研究生和本科生的支持，并与俄勒冈海洋生物研究所的NSF资助的海洋科学教育卓越中心(COSEE)计划相结合，将该项目的培训和经验带给社区大学教授。

The prevalence in bacterioplankton genomes of specialized genes for the metabolism of volatile organic compounds is a "smoking gun" that points to a hidden VOC cycle potentially of significant magnitude. With funding provided through this EArly-concept Grant for Exploratory Research (EAGER), researchers at Oregon State University and the University of Colorado at Boulder will gather new evidence about the VOC cycle in the ocean photic zone by: 1) measuring the turnover rates of VOC compounds by plankton communities on a Surface Ocean Lower Atmosphere (SOLAS) cruise, and 2) identifying the organisms and biochemical machinery that mediate VOC oxidation. This research is potentially transformative because quantitative evidence indicating significant VOC cycling would cause an overhaul of carbon cycle models and focus attention on specialized metabolic processes that have received little attention and are poorly characterized. This research is high risk for similar reasons: while mounting evidence points to a significant "hidden carbon cycle", its importance will not be known until its magnitude is measured, and the achievement of this goal requires an investment in specialized knowledge and technology.The project is a collaboration between atmospheric chemists and marine microbiologists who bring together the knowledge and technology needed to solve this problem on a SOLAS cruise and in a laboratory setting. Measurements of the seawater concentrations of VOC compounds (e.g. methanol, formaldehyde, dimethylsulfide, trimethyamine, trimethylamine oxide, acetonitrile, acetone, isoprene, glyoxal, methylglyoxal and acetaldehyde) and turnover rates determined by the incubation of isotopically-labeled compounds with microbial plankton suspensions will provide information about variation in these geochemical processes across a transect that extends from a productive continental shelf to an oligotrophic subtropical gyre. Later the same team will measure the production and oxidation of these compounds by microbial isolates in a controlled setting, focusing on biochemical pathways that oxidize one carbon (C1) units from Oxidized VOC (OVOC) and methylated dissolved organic carbon (MDOC). Comprehensive measurements of microbial diversity in the field and transcriptome responses in the laboratory will set the stage for future research linking VOC cycling to specific organisms, metabolic pathways and genes, and for understanding when, and in response to what selective pressures, the microbial community engages in these processes.Broader Impacts: VOCs play varied and important roles in atmospheric chemistry, acting as precursors for photochemical formation of ozone and aerosol, i.e. two secondary pollutants that also affect the radiative forcing of climate. Information about biological sources and sinks of VOCs in the ocean surface could result in a better understanding of the underlying causes of variation in air/sea VOC fluxes, and potentially could alter predictions about the impact of climate change on ocean surface ecology and air/sea interactions. Additionally, the project will address biochemical mechanisms that underlie VOC cycling and should provide experimental evidence about relevant gene functions. Therefore, revised gene annotations resulting from this work could improve the accuracy of future predictions of VOC metabolism made from genomes and metagenomes. This proposal includes support for postdocs, graduate and undergraduate students and is integrated with the Oregon Institute of Marine Biology's NSF funded Center for Ocean Sciences Education Excellence (COSEE) program, bringing training and experience from this project to community college professors.