CAREER: Investigating aerobic microbial respiration dynamics in coastal hypoxia

海洋溶解氧（DO）的减少是一个普遍的、日益严重的全球性问题。沿海溶解氧损失的主要原因是人为营养物输入，导致季节性缺氧-溶解氧浓度低于2毫克/升。微生物是氧气去除的主要因素，尽管我们对营养富集如何与分层相结合以刺激微生物代谢和氧气下降有基本的机械理解，但我们仍然不知道哪些微生物最终负责导致氧气消耗，以及在任何特定区域的沿海缺氧期间。我们也不知道每个缺氧系统在多大程度上来自于普遍的微生物机制，或者是否有独特的微生物和代谢途径参与每个区域。在地球仪周围，缺氧区的数量和面积都在增加，这就需要更好地了解负责氧气消耗的微生物过程。作为回应，该项目致力于综合研究和教育工作，以研究在发生溶解氧耗竭的两个沿海地区氧气呼吸的微生物机制：墨西哥湾北方“死亡区”和南加州湾。这项工作确定了在这些系统中积极消耗氧气的微生物，是什么为它们提供燃料，以及这些类群是否/如何对环境变化做出反应。研究人员正在生成微生物DO消耗率，遗传和分类学数据，这些数据对于更好地约束专注于水柱DO消耗的呼吸模型至关重要。在这样做的过程中，数百名本科生和学生以及数十名高中STEM教师通过参与现代海洋微生物研究贡献了宝贵的数据。该项目还提高了真实的研究经验融入大学和高中课堂的背景下，一个全球性的relevance.Regions的低溶解氧采取多种形式，从广阔的开放海洋氧气最小区（OMZs），在上层水柱盘旋，以浅水区的底层水缺氧靠近河流输入人类提供的营养物燃料。微生物呼吸主要负责DO的最终消耗，因此了解栖息在这些系统中的微生物及其代谢能力对于提高我们预测DO消耗的时间，程度和严重程度以及这些因素如何与环境变化相关的能力至关重要。虽然已经有大量的研究OMZ的微生物学，我们知道相对较少的微生物动力学，特别是微生物负责耗氧，在沿海缺氧。这一综合研究和教育工作的框架是由以下目标：1。确定微生物和代谢过程负责积极呼吸水柱DO之前，和期间，缺氧。2.对群落和代表性水柱物种的微生物呼吸速率进行量化，包括浮游和颗粒相关部分。将关于全球相关主题的真实微生物学研究整合到本科和高中课堂中。这项工作使用先进的培养独立和纯培养测量的组合来区分浮游和颗粒相关微生物组分的耗氧量，以及表面和底部沃茨中的群落，在两个不同的沿海溶解氧消耗系统（墨西哥湾北方缺氧区和南加州沿海大陆架）。对活跃呼吸类群的直接评估与它们的代谢潜力、基因表达和呼吸速率有关。该项目首次确定了这些系统中积极消耗氧气的分类群。结果还提供了跨多个地点和季节的深度的大小分级呼吸速率和细菌生长效率（BGE），并且重要的是，还产生这些系统内的活性分类群的细胞特异性呼吸速率和BGE。这些数据将限制不同环境条件下的可变呼吸。研究人员正在实验性地测试环境变量的变化如何影响这些呼吸速率和BGE，从而对气候强迫对DO消耗的影响范围有更好的预测性见解。这些信息也有助于多个海洋系统之间的比较，以确定是否共同或不同的生物体和代谢过程的运作，以消除DO。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Decreasing marine dissolved oxygen (DO) is a widespread and growing global problem. Among the chief causes for coastal losses of DO are anthropogenic nutrient inputs that lead to seasonal hypoxia- DO concentrations below 2 mg/L. Microorganisms are the primary agents of oxygen removal, and although we have a basic mechanistic understanding of how nutrient enrichment combines with stratification to stimulate microbial metabolism and oxygen drawdown, we still do not know which microorganisms are ultimately responsible for oxygen consumption leading to, and during, coastal hypoxia in any particular region. Nor do we know the extent to which each hypoxic system arises from universal microbial mechanisms or whether there may be unique microorganisms and metabolic pathways involved in each locale. Hypoxic regions are increasing in number and size around the globe, amplifying the need to better understand the microbial processes responsible for oxygen consumption. In response, the project pursues an integrated research and education effort to study the microbial mechanisms of oxygen respiration in two coastal zones where DO depletion occurs: the northern Gulf of Mexico “dead zone”, and the Southern California Bight. This work identifies the microorganism actively consuming oxygen in these systems, what fuels them, and whether/how those taxa respond to environmental changes. The investigators are generating microbial DO consumption rate, genetic, and taxonomic data critical to better constraining respiration models focused on water column DO depletion. In doing so, hundreds of undergraduate and students and dozens of high school STEM teachers contribute valuable data by participating in modern marine microbiological research. The project also improves integration of authentic research experiences into college and high-school classrooms in the context of a problem of global relevance.Regions of low DO take multiple forms, from vast open ocean oxygen minimum zones (OMZs) which hover in the upper water column, to shallower coastal zones of bottom water hypoxia fueled by close proximity to fluvial inputs of human supplied nutrients. Microbial respiration is primarily responsible for the ultimate consumption of DO, and therefore understanding the microorganisms that inhabit these systems and their metabolic capabilities is critical for improving our ability to predict the timing, extent, and severity of DO depletion, and how these factors relate to environmental change. While there has been substantial research into the microbiology of OMZs, we know comparatively little about the microbial dynamics, and in particular, the microorganisms responsible for oxygen consumption, in coastal hypoxia. This integrated research and education effort is framed by the following objectives:1. Determine the microorganisms and metabolic processes responsible for actively respiring water column DO prior to, and during, hypoxia.2. Quantify microbial respiration rates for communities and representative water column species in both the planktonic and particle-associated fractions.3. Integrate authentic microbiology research on a globally relevant topic into undergraduate and high school classrooms.The work uses a combination of advanced cultivation-independent and pure culture measurements to discriminate between oxygen consumption by planktonic and particle-associated microbial fractions, as well as by communities at the surface and those in bottom waters, in two different systems of coastal DO depletion (the northern Gulf of Mexico hypoxic zone and the Southern California coastal shelf). Direct assessment of actively respiring taxa are connected with their metabolic potential, gene expression, and respiration rates. This project is determining, for the first time, the taxa actively consuming oxygen in these systems. The results also provide size fractionated respiration rates and bacterial growth efficiency (BGE) with depth across multiple sites and seasons, and importantly, also yield cell-specific respiration rates and BGE for active taxa within these systems. This data will constrain variable respiration across differing environmental conditions. The investigators are experimentally testing how alterations in environmental variables affect these respiration rates and BGEs, leading to greater predictive insight for the range of effects climate forcing will have on DO consumption. This information also facilitates comparisons between multiple marine systems to identify whether common or distinct organisms and metabolic processes are operating to remove DO.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.