CAREER: Investigating aerobic microbial respiration dynamics in coastal hypoxia

海洋溶解氧（DO）减少是一个普遍且日益严重的全球性问题。沿海DO损失的主要原因之一是人为的养分输入导致季节性缺氧- DO浓度低于2 mg/L。微生物是除氧的主要媒介，尽管我们对营养富集与分层结合刺激微生物代谢和氧气减少的机制有基本的了解，但我们仍然不知道哪些微生物最终负责氧气消耗，导致任何特定地区的沿海缺氧。我们也不知道每个缺氧系统在多大程度上是由普遍的微生物机制产生的，也不知道每个地方是否有独特的微生物和代谢途径。在全球范围内，缺氧区域的数量和面积都在增加，这就加大了更好地了解微生物耗氧过程的必要性。作为回应，该项目进行了综合研究和教育工作，以研究两个沿海地区氧呼吸的微生物机制，这些地区发生了DO损耗：墨西哥湾北部“死亡区”和南加州海湾。这项工作确定了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，以及这些分类群是否/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、遗传和分类数据，这些数据对于更好地限制以水柱DO消耗为重点的呼吸模型至关重要。在此过程中，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。该项目还改善了在全球相关问题背景下将真实的研究经验融入大学和高中课堂的情况。低溶解氧的区域有多种形式，从悬停在上层水柱上的广阔的开放海洋最低氧区（OMZs），到由于接近人类提供的营养物质的河流输入而导致的底部水缺氧的较浅沿海地区。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与环境变化的关系的能力至关重要。虽然对omz的微生物学进行了大量研究，但我们对微生物动力学知之甚少，特别是对沿海缺氧中负责耗氧的微生物知之甚少。这一综合研究和教育工作有以下目标：确定在缺氧之前和期间负责主动呼吸水柱DO的微生物和代谢过程。量化浮游生物和颗粒相关部分中群落和代表性水柱物种的微生物呼吸速率。在本科和高中课堂上整合全球相关主题的真实微生物学研究。这项工作结合了先进的培养独立和纯培养测量来区分浮游生物和颗粒相关微生物组分的耗氧量，以及在两个不同的沿海DO耗竭系统（墨西哥湾北部缺氧区和南加州沿海大陆架）中表层和底层水域的群落的耗氧量。主动呼吸类群的直接评估与它们的代谢潜能、基因表达和呼吸速率有关。该项目首次确定了这些系统中主动消耗氧气的分类群。结果还提供了在多个位点和季节中深度的大小分步呼吸速率和细菌生长效率（BGE），重要的是，也得到了这些系统中活性分类群的细胞特异性呼吸速率和BGE。这些数据将约束不同环境条件下的可变呼吸。研究人员正在实验测试环境变量的变化如何影响这些呼吸速率和BGEs，从而对气候强迫对DO消耗的影响范围有更大的预测性见解。这些信息还有助于在多个海洋系统之间进行比较，以确定共同或独特的生物和代谢过程是否在去除DO。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。

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.