Microbial processes of pelagic anaerobic methane cycling in oxygen minimum zones

这项研究的首要目标是了解海洋最小氧区（OMZs）中的细菌如何控制海洋甲烷和氮循环之间的相互作用。 OMZ构成了海洋水柱中最大的甲烷池，也是厌氧微生物将必需元素氮从生物体可以使用的形式转化为可以从海洋中丢失的气态形式（N2）的场所。 最近的研究，主要是在淡水环境中，已经发现了将甲烷消耗与氮损失途径联系起来的新型细菌。 这些研究人员最近表明，这种细菌也存在于OMZ中。 然而，这些细菌对海洋甲烷和氮通量的贡献仍然未知。 在这里，研究人员将使用基因组学和生化测量的组合来表征这些细菌在OMZ中的代谢潜力和多样性，并量化它们对甲烷和氮转化的贡献。 实现这一目标对于限制这些化学品在公海中的大量通量和气候变化预测模型至关重要，特别是考虑到甲烷作为一种强有力的温室气体的重要性以及有机MZ将随着全球变暖而扩大的预测。 该项目还致力于提高公共竞技场和教育界对海洋微生物学的认识。 研究人员将把这项研究的结果和概念纳入格鲁吉亚理工学院海洋科学夏季研讨会（SWiMS）的教学模块中（https：//swimsgatech.wordpress.com/），这是一个年度研讨会，旨在通过讲座和实验室练习来培训海洋科学的初中和高中教育工作者。该项目还将通过格鲁吉亚技术礼品计划培训本科生、博士后和当地高中教师。 通过结合研究和教育活动，这项研究将确定海洋中的低氧条件如何调节浮游微生物多样性和甲烷循环，以及告知，参与和激发科学和普通观众对海洋微生物学和海洋地球化学的兴趣。 本研究特别关注进行亚硝酸盐依赖的厌氧甲烷氧化（n-damo）的细菌。 该过程已经在NC 10区的细菌中描述，其中歧化反应产生N2和O2气体，其中O2用于内好氧甲烷氧化。 虽然NC 10细菌主要来自富含亚硝酸盐的淡水和海洋沉积物，但最近的证据表明，NC 10也存在于缺氧的OMZ中。 考虑到OMZ含有大量的n-damo底物亚硝酸盐和甲烷，假设OMZ具有与氮损失偶联的厌氧甲烷循环，并且这种偶联是由在不同OMZ中作为普遍存在的组分出现的n-damo NC 10细菌介导的。 为了验证这一假设，研究人员将1）量化n-damo对OMZ甲烷氧化，N2生产和氧气生产速率的贡献，2）通过富集和单细胞基因组学表征OMZ NC 10分离株的多样性和生态生理学，3）调查NC 10细菌在不同OMZ系统中的丰度，多样性和活性。

The overarching goal of this research is to understand how bacteria in marine oxygen minimum zones (OMZs) control interactions between the ocean methane and nitrogen cycles. OMZs constitute the largest pool of methane in the ocean water column, and also serve as sites where anaerobic microbes convert the essential element nitrogen from a form that can be used by organisms to a gaseous form (N2) that can be lost from the ocean. Recent studies, predominantly in freshwater environments, have discovered novel bacteria that link methane consumption to pathways of nitrogen loss. These researchers have recently shown that such bacteria also occur in OMZs. However, the contributions of these bacteria to ocean methane and nitrogen flux remain unknown. Here, the researchers will use a combination of genomics and biochemical measurements to characterize the metabolic potential and diversity of these bacteria in OMZs and to quantify their contribution to methane and nitrogen transformations. Meeting this goal is critical for constraining bulk fluxes of these chemicals in the open ocean and for predictive models of climate change, notably given the importance of methane as a potent greenhouse gas and the prediction that OMZs will expand with global warming. This project is also committed to enhancing knowledge of marine microbiology in the public arena and educational communities. The investigators will incorporate results and concepts from this research into instructional modules for use in the Summer Workshop in Marine Science (SWiMS) at Georgia Tech (https://swimsgatech.wordpress.com/), an annual workshop to train middle and high school educators in marine science using lectures and lab exercises. This project will also involve training of undergraduate students, a postdoc, and local high school teachers through the Georgia Tech GIFT Program. Through the combined research and educational activities, this research will determine how low-oxygen conditions in the ocean regulate pelagic microbial diversity and methane cycling, as well as inform, engage, and excite scientific and general audiences about marine microbiology and biogeochemistry. This research focuses specifically on bacteria conducting nitrite-dependent anaerobic methane oxidation (n-damo). This process has been described in bacteria of the NC10 division, in which a dismutation reaction generates both N2 and O2 gas, with the O2 used for intra-aerobic methane oxidation. Although NC10 bacteria have been described primarily from nitrite-rich freshwater and marine sediments, recent evidence indicates that NC10 are also present in anoxic OMZs. Given that OMZs contain substantial pools of the n-damo substrates nitrite and methane, it is hypothesized that OMZs harbor an anaerobic methane cycle coupled to nitrogen loss, and that this coupling is mediated by n-damo NC10 bacteria that occur as ubiquitous components in diverse OMZs. To test this hypothesis, the researchers will 1) quantify the contribution of n-damo to OMZ methane oxidation, N2 production, and oxygen production rates, 2) characterize the diversity and ecophysiology of OMZ NC10 isolates through enrichments and single-cell genomics, and 3) survey the abundance, diversity, and activity of NC10 bacteria across distinct OMZ systems.