Collaborative Research: Key Microbial Processes in Oxygen Minimum Zones: From In Situ Community Rate Measurements to Single Cells

氧气的可获得性决定了海洋生物的分布和活动。持续不断的人类活动和气候变化预计将导致沿海和开阔海洋本已大面积的氧气紧张地区的扩大和加剧。海洋氧气的减少具有重大的生态后果，包括迁徙生物和海底生物的栖息地丧失，海洋食物网的改变，以及产生对气候有明显反馈的微量气体，如甲烷和一氧化二氮。微生物的剧烈化学循环发生在缺氧的海洋栖息地。然而，由于对关键微生物过程的实际速率和调节这些过程的微生物的动力学的了解有限，对海洋生态系统的后果的充分了解受到阻碍。这项研究结合了新的方法和采样技术，以了解这些过程如何受到氧气浓度变化的影响，以预测不断变化的海洋中的重要化学交换及其气候活跃气体的产生。这个深度合作的项目培养了本科生(其中四人参加了邮轮)、一名研究生和一名博士后研究员。在初中和高中，通过社交媒体进行外展。游轮上的数据和样本被整合到课程中。氧气的枯竭改变了主要元素(特别是碳、氮和硫)的循环以及食物链的功能。该项目通过应用原位方法更准确地测量海洋生物地球化学循环中几个关键微生物过程(化学自养、反硝化、厌氧氨氧化、硫酸盐还原和硫化物氧化)的速率，解决了我们在氧最小区域(OMZ)过程方面的主要知识空白。这项工作研究了东热带北太平洋OMZ，最大的开放海洋耗氧系统，以1)确定参与碳、氮和硫循环的微生物过程的原位速率，2)揭示参与这些过程的活跃单细胞的基因组蓝图，以及3)估计主要的化学自养和异养类群对测量速率的相对贡献。这项工作包括应用尖端设备进行现场采样和培养，将与传统水采样方法相关的人工制品降至最低，从而能够更准确地估计重要的生物地球化学过程的速率。此外，对相对未受干扰的散装和分馏水样进行速率测量，可以更容易地区分与颗粒相关的微生物在这些OMZ过程中的潜在作用。利用指示细胞活性的荧光染料与转录物一起对微生物进行单细胞分选，可以了解活跃的微生物群落成员用于关键过程的代谢途径，以及化学自养和氮或/和硫循环的潜在耦合。通过结合稳定同位素探测、荧光原位杂交和单细胞拉曼显微光谱分析，评估了参与化学自养和异养元素循环的不同微生物类群的相对活动水平。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Oxygen availability shapes the distributions and activities of marine organisms. Ongoing human activities and climate change are expected to lead to expansion and intensification of already large oxygen-stressed areas of the coastal and open ocean. Decreases in ocean oxygen have significant ecological consequences, including habitat loss for migratory and bottom-dwelling organisms, modification of the marine food web, and production of trace gases with pronounced feedbacks on climate, such as methane and nitrous oxide. Intense chemical cycling by microorganisms occurs in oxygen-depleted marine habitats. However, a full understanding of the consequences for marine ecosystems is hampered by limited knowledge of actual rates of key microbiological processes and dynamics of the microorganisms mediating them. This study combines novel methods and sampling techniques to understand how these processes are influenced by changes in oxygen concentration to inform predictions of important chemical exchanges within a changing ocean and its production of climate-active gases. This deeply collaborative project trains undergraduates (four of whom participate on the cruise), a graduate student and a postdoctoral fellow. Outreach takes place in middle and high schools and through social media. Data and samples from the cruise are integrated in coursework.Oxygen depletion alters cycling of major elements (especially carbon, nitrogen, and sulfur) as well as food web functionality. This project addresses major gaps in our knowledge of oxygen minimum zone (OMZ) processes by applying in situ approaches to more accurately measure rates of several key microbial processes (chemoautotrophy, denitrification, anammox, sulfate reduction and sulfide oxidation) central to marine biogeochemical cycling. This work studies the Eastern Tropical North Pacific OMZ, the largest open ocean oxygen-depleted system, to 1) determine the in situ rates of microbial processes involved in carbon, nitrogen, and sulfur cycling, 2) reveal the genomic blueprint of active single cells involved in these processes, and 3) obtain estimates of the relative contributions of the dominant chemoautotrophic and heterotrophic groups to the measured rates. This work include applies cutting-edge equipment for in situ sampling and incubations that minimize artifacts associated with traditional water sampling approaches, allowing more accurate estimates of rates of important biogeochemical processes. Additionally, rate measurements of relatively undisturbed bulk and fractionated water samples make it easier to distinguish the potential role of particle-associated microorganisms in these OMZ processes. Single cell sorting of microorganisms using a fluorescent dye indicative of cell activity together with metatranscriptomics informs on metabolic pathways used for key processes by active microbial community members, as well as the potential coupling of chemoautotrophy and nitrogen or/and sulfur cycling. By combining stable isotope probing, fluorescence in situ hybridization and single cell Raman microspectrometry the relative activity levels of different microbial phylotypes involved in chemoautotrophic and heterotrophic elemental cycling are assessed.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.