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

氧气的可用性决定了海洋生物的分布和活动。预计持续的人类活动和气候变化将导致已经很大的沿海和公海缺氧地区的扩大和加剧。海洋氧气的减少具有重要的生态后果，包括迁徙和海底生物栖息地的丧失，海洋食物网的改变，以及对气候有明显反馈的微量气体的产生，如甲烷和一氧化二氮。在缺氧的海洋环境中，微生物会进行剧烈的化学循环。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动力学的了解有限，对海洋生态系统后果的充分理解受到了阻碍。这项研究结合了新颖的方法和采样技术，以了解这些过程如何受到氧浓度变化的影响，从而为不断变化的海洋中重要的化学交换及其产生的气候活性气体的预测提供信息。这个深度合作的项目培养本科生（其中四人参加游轮），一名研究生和一名博士后。外展活动在初中和高中进行，并通过社交媒体进行。从巡航数据和样本被整合到课程作业中。氧气的消耗改变了主要元素（尤其是碳、氮和硫）的循环以及食物网的功能。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核心的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，解决了我们对氧最小区（OMZ）过程知识的主要空白。本研究研究了东部热带北太平洋OMZ，最大的开放海洋缺氧系统，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性单细胞的基因组蓝图，以及3)获得优势化自养和异养群体对测量速率的相对贡献的估计。这项工作包括应用尖端设备进行原位采样和孵卵，最大限度地减少与传统水样方法相关的人工影响，从而更准确地估计重要生物地球化学过程的速率。此外，相对未受干扰的散装和分馏水样的速率测量使其更容易区分颗粒相关微生物在这些OMZ过程中的潜在作用。利用指示细胞活性的荧光染料和亚转录组学对微生物进行单细胞分选，可以了解活跃微生物群落成员在关键过程中使用的代谢途径，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法，评估了参与化学自养和异养元素循环的不同微生物种类的相对活性水平。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.