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，因此对气候和地球的主要营养循环至关重要。绝大多数海洋表面的营养物质相对枯竭，这些营养物质是生物生长所必需的。对于距离海岸数百或数千英里、海底数千米的海洋漩涡来说，情况尤其如此。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激烈。光合作用群落中最丰富的成员，单细胞细菌原氯球菌，也是最小的，长度只有半微米。有趣的是，原氯球菌对过氧化氢等活性氧物种(ROS)非常敏感，在没有“辅助”微生物的情况下无法生长，这些微生物可以为阳光与海水中的有色有机物反应产生的ROS解毒。原氯球菌对助手的真正依赖程度目前尚不清楚：到目前为止，实验只评估了原氯球菌在ROS胁迫下在其他最佳生长条件下的存活情况，这在自然环境中是罕见的。最近有证据表明，原氯球菌和助手可以竞争营养，这又增加了一层复杂性。该项目结合了实验养殖工作、野外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。实验室培养的原氯球菌和其他微生物正在接受检测，看它们在不同营养浓度、温度和光照强度下，单独生长和相互混合培养时，在ROS下的生长和存活变化。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，正在将实验室结果和数学模型与北太平洋暴露在一系列ROS浓度下的自然群落进行比较。通过这种方式，这项研究正在发展一个更深入和更具预测性的理解，即微生物群落的组成和死亡率如何取决于ROS的产生和衰退。该项目的更广泛影响包括对本科生和研究生进行海洋学研究方面的培训，并向当地诺克斯维尔社区以及现役海军陆战队家属宣传微生物学和海洋学。该项目的总体目标是通过实验室实验和野外操作相结合的方式对生态系统模型进行经验性的参数化，以探索HoOH和寡营养微生物群落的耦合动力学。原氯球菌是贫营养海洋中最丰富的浮游植物，对全球碳循环有重要贡献。其丰富性的关键在于其在营养方面胜过其他微生物的能力。这种生态优势被认为涉及基因组流线型的进化过程，包括失去过氧化氢(HoOH)抗性机制，以及原氯球菌依赖微生物群落在阳光照射下的表面混合层降解光化学产生的HoOH。然而，当温度偏离最佳温度时，原氯球菌对HoOH的敏感性--从而对助手的依赖--就会增加。同样的道理也适用于光照和营养条件。同样，人们对HOOH解毒“辅助”微生物的环境敏感性知之甚少，包括浮游植物群落的其他成员。因此，原氯球菌需要帮助的程度，以及不同的消耗氢氧化氢的微生物提供这种功能的程度，目前尚不清楚。该项目正在提供HoOH和微生物动力学的定量测量，以了解表面混合层中微生物群落的聚集规律。几种原氯球菌、潜在的助手和竞争对手的微生物正在恒化器中的一系列营养限制和Hooh条件下生长，以评估生长、死亡和--对于浮游植物--光合作用。与其他微生物的共培养，包括聚球藻和几种光合作用的微真核生物，正在被用来测试关于HoOH解毒和竞争对原氯球菌-ROS动态的影响的假说在最佳和次优条件下，这些生态系统模型预测与现场操作一起解释，这些现场操作直接评估ROS在其他损失过程中的影响，主要是放牧和病毒裂解。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。

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.