Characterizing the effects of exogenous reactive oxygen species on marine microbial ecosystem dynamics

构成海洋浮游植物群落的微生物约占地球上所有光合作用的一半，因此对地球的气候和主要营养循环至关重要。绝大多数海洋表面相对来说缺乏生物生长所必需的营养物质。对于距离海岸数百或数千英里，海底数千米以上的海洋环流来说尤其如此。在这些地区，不同浮游植物之间对营养物质的竞争被认为特别强烈。光合作用群落中最丰富的成员，单细胞细菌原绿球藻，也是最小的，长度为半微米。有趣的是，原绿球藻对活性氧（ROS）如过氧化氢非常敏感，并且在没有“辅助”微生物的情况下不能生长，这些“辅助”微生物在阳光与海水中的有色有机物质反应时产生ROS解毒。原绿球藻依赖于辅助物的真实程度目前尚不清楚：到目前为止，实验仅评估了原绿球藻在自然环境中罕见的最佳生长条件下的ROS胁迫下的存活。最近有证据表明原绿球藻和辅助球藻可以竞争营养物质，这增加了另一层复杂性。该项目结合了实验培养工作，实地测量和生态系统建模，以表征ROS在表层海洋群落动态中的作用。原绿球藻和其他微生物的实验室培养物正在检查生长和生存的变化时，暴露于ROS下的营养浓度，温度和光强度的范围内，当单独生长和共同培养彼此。实验室实验的结果随后被用于数学生态系统模型，以模拟自然海洋环境。最后，实验室的结果和数学模型进行了比较，自然社区在北太平洋暴露于一系列的活性氧浓度。通过这种方式，这项研究正在对微生物群落组成和死亡率如何取决于ROS的产生和衰减进行更深入和更预测性的了解。该项目的更广泛影响包括对海洋学研究的本科生和研究生进行培训，以及向当地诺克斯维尔社区以及现役海军陆战队员的家属宣传微生物学和海洋学。该项目的总体目标是使用实验室实验和现场操作相结合的经验参数化生态系统模型，以探索HOOH和寡营养微生物群落的耦合动力学。原绿球藻是贫营养海洋中最丰富的植物浮游生物，对全球碳循环有重要贡献。其丰富的关键是它能够胜过其他微生物的营养。这种生态优势被认为涉及基因组精简的进化过程，包括过氧化氢（HOOH）抗性机制的丧失和原绿球藻对微生物群落的依赖，以降解阳光暴露的表面混合层中光化学产生的HOOH。然而，当温度偏离最佳温度时，原绿球藻对HOOH的敏感性-从而对辅助物的依赖性-会增加。这同样适用于光照和营养条件。同样，对于HOOH解毒“助手”微生物（包括浮游植物群落的其他成员）的环境敏感性也知之甚少。因此，原绿球藻需要帮助的程度，以及不同的HOOH消耗微生物提供这种功能的程度，目前尚不清楚。本计画提供微生物动力学及热氧自由基之定量量测，以了解混合层表面微生物群落之聚集规律。几株原绿球藻，潜在的助手，和竞争对手的微生物正在生长在一系列的营养限制和HOOH条件下的恒化器，以评估生长，死亡率，和-浮游植物-光合作用。与其他微生物的共培养，包括聚球藻和几种光合微真核生物，正在被用来测试关于HOOH解毒的假设，以及在最佳和次最佳条件下竞争对原绿球藻-ROS动力学的影响。这些生态系统模型预测正在与现场操作一起解释，这些操作直接评估其他损失过程中ROS介导的影响，该奖项反映了NSF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。

The microbes that constitute the phytoplankton community of the ocean account for about half of all photosynthesis on the earth and as a consequence are critically important to the climate and major nutrient cycles of the planet. The vast majority of the ocean surface is relatively depleted in nutrients essential for organisms to grow. This is especially true for the ocean gyres that are hundreds or thousands of miles from the coast and thousands of meters above the ocean floor. In these regions, competition among different phytoplankton for nutrients is thought to be especially strong. The most abundant member of the photosynthetic community, the single-celled bacterium Prochlorococcus, is also its smallest, measuring a half a micrometer in length. Interestingly, Prochlorococcus is very sensitive to reactive oxygen species (ROS) such as hydrogen peroxide and cannot grow in the absence of “helper” microbes which detoxify the ROS generated when sunlight reacts with pigmented organic material in the seawater. The true extent to which Prochlorococcus depends on helpers is currently unknown: thus far, experiments have only assessed Prochlorococcus survival of ROS stress under otherwise optimal growth conditions which are rare in the natural environment. Recent evidence that Prochlorococcus and helpers can compete for nutrients adds another layer of complexity. This project combines experimental culture work, field measurements, and ecosystem modeling to characterize the roles of ROS in surface ocean community dynamics. Laboratory cultures of Prochlorococcus and other microbes are being examined for growth and survival changes when exposed to ROS under a range of nutrient concentrations, temperatures, and light intensities, when grown separately and in co-culture with each other. Outcomes from the laboratory experiments are then being used in mathematical ecosystem models to simulate the natural marine environment. Finally, laboratory results and mathematical models are being compared to natural communities in the North Pacific Ocean exposed to a range of ROS concentrations. In this way, this research is developing a deeper and more predictive understanding of how microbial community composition and mortality depend upon ROS production and decay. Broader impacts of the project include the training of undergraduate and graduate students in oceanographic research and public outreach about microbiology and oceanography to the local Knoxville community, as well as dependents of active duty Marines. The overarching goal of this project is to empirically parameterize ecosystem models using a combination of lab experiments and field manipulations to explore the coupled dynamics of HOOH and oligotrophic microbial communities. Prochlorococcus is the most abundant phytoplankter in the oligotrophic ocean and contributes significantly to global carbon cycling. Key to its abundance is its ability to outcompete other microbes for nutrients. This ecological advantage is thought to involve an evolutionary process of genomic streamlining, including a loss of hydrogen peroxide (HOOH) resistance mechanisms and reliance of Prochlorococcus on the microbial community to degrade photochemically-generated HOOH in the sun-exposed surface mixed layer. When temperature deviates from optimal, however, sensitivity of Prochlorococcus to HOOH – and thus reliance upon helpers - is heightened. The same may hold true for light and nutrient conditions. Similarly, little is known about the environmental sensitivity of HOOH-detoxifying “helper” microbes, including fellow members of the phytoplankton community. Therefore, the extent to which Prochlorococcus requires help, and to which different HOOH-consuming microbes provide this function, is not currently understood. This project is providing the quantitative measurements in HOOH and microbial dynamics to understand the rules of microbial community assembly in the surface mixed layer. Several strains of Prochlorococcus, potential helper, and competitor microbes are being grown under a range of nutrient-limiting and HOOH conditions in chemostats to assess growth, mortality, and - for the phytoplankton – photosynthesis. Co-cultures with the other microbes, including Synechococcus and several photosynthetic picoeukaryotes, are being used to test hypotheses about HOOH detoxification and the impacts of competition on Prochlorococcus–ROS dynamics under optimal and suboptimal conditions These ecosystem model predictions are being interpreted alongside field manipulations which directly assess ROS mediated impacts in the context of other loss processes, primarily grazing and viral lysis.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.