CAREER: Understanding Microbial Heterotrophic Processes in Coastal Antarctic Waters

南极沿海地区正经历着巨大的环境变化。环境中的物理变化，如海冰持续时间和范围的改变，对构成海洋食物网基础的浮游植物和细菌物种有直接影响。光合作用的浮游植物是海洋的主要生产者，它们将二氧化碳转化（固定）为有机碳分子，并为浮游动物和大型捕食者提供食物来源。当浮游植物被浮游动物消耗或被病毒杀死时，它们会向环境中释放大量的有机碳和营养物质。异养细菌必须吃其他东西，并发挥“主回收者”的作用，消耗这些物质并将其转化为细菌生物量，这些生物量可以养活更大的生物，如原生生物。一些原生生物是异养生物，但其他的是混合营养体，能够通过光合作用或异养生长。先前的研究表明，原生生物和病毒可以通过杀死和食用细菌来调节细菌数量，但人们对南极水域如何调节这些过程知之甚少。该项目将通过实验确定南极原生生物消耗细菌的速度，并通过实地研究确定参与碳吸收和再循环的主要细菌类群。此外，该项目将利用新的测序技术获得许多南极海洋细菌的完整基因组。为了将这项工作置于生态系统背景下，该项目将使用微生物多样性数据来告知PALMER生态系统模型中与关键微生物过程相关的比率。该项目解决了关于南极沿海异养海洋细菌的生态作用和细菌种群的自上而下控制的关键未知数。以前的研究表明，在一年中的某些时候，异养和混合养原生生物的放牧可能达到或超过细菌的产量。同样，在较温和的水域中，噬菌体（病毒）被认为是春季和夏季细菌死亡的重要原因。这些不同的自上而下的控制对海洋食物网中的碳流有影响，因为原生生物比细菌更容易被更高的营养水平所吞噬。该项目将结合放牧实验和实地观察来评估温带噬菌体和原生生物造成的死亡率的时间动态。虽然在南极沿海观察到的许多异养菌株在分类上与来自其他地区的菌株相似，但最近的研究表明它们在系统发育和遗传上是不同的。为了更好地了解南极关键海洋细菌的生态功能和进化轨迹，将对其基因组进行分离和测序。然后，这些基因组将用于改进非洲豆代谢推断管道的预测，以及我们对南极海洋环境中异养细菌与其主要捕食者之间关系的理解。最后，研究人员将对区域试验台模型进行修改，使微生物多样性数据能够用于优化关键参数的起始条件，并约束模型的数据同化方法。这个项目有一个广泛的教育和推广组成部分，旨在让学生和公众参与以南极微生物群和海洋科学为中心的各种活动。一个关于南极海洋科学的新模块将为广受欢迎的Sally Ride science项目开发，加州大学圣地亚哥分校现有的两门本科课程将加强，引入新兴技术的实验室模块和前沿的极地科学。本项目资助博士生1名，博士后1名。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。

The coastal Antarctic is undergoing great environmental change. Physical changes in the environment, such as altered sea ice duration and extent, have a direct impact on the phytoplankton and bacteria species which form the base of the marine foodweb. Photosynthetic phytoplankton are the ocean's primary producers, transforming (fixing) CO2 into organic carbon molecules and providing a source of food for zooplankton and larger predators. When phytoplankton are consumed by zooplankton, or killed by viral attack, they release large amounts of organic carbon and nutrients into the environment. Heterotrophic bacteria must eat other things, and function as "master recyclers", consuming these materials and converting them to bacterial biomass which can feed larger organisms such as protists. Some protists are heterotrophs, but others are mixotrophs, able to grow by photosynthesis or heterotrophy. Previous work suggests that by killing and eating bacteria, protists and viruses may regulate bacterial populations, but how these processes are regulated in Antarctic waters is poorly understood. This project will use experiments to determine the rate at which Antarctic protists consume bacteria, and field studies to identify the major bacterial taxa involved in carbon uptake and recycling. In addition, this project will use new sequencing technology to obtain completed genomes for many Antarctic marine bacteria. To place this work in an ecosystem context this project will use microbial diversity data to inform rates associated with key microbial processes within the PALMER ecosystem model. This project addresses critical unknowns regarding the ecological role of heterotrophic marine bacteria in the coastal Antarctic and the top-down controls on bacterial populations. Previous work suggests that at certain times of the year grazing by heterotrophic and mixotrophic protists may meet or exceed bacterial production rates. Similarly, in more temperate waters bacteriophages (viruses) are thought to contribute significantly to bacterial mortality during the spring and summer. These different top-down controls have implications for carbon flow through the marine foodweb, because protists are grazed more efficiently by higher trophic levels than are bacteria. This project will use a combination of grazing experiments and field observations to assess the temporal dynamics of mortality due to temperate bacteriophage and protists. Although many heterotrophic bacterial strains observed in the coastal Antarctic are taxonomically similar to strains from other regions, recent work suggest that they are phylogenetically and genetically distinct. To better understand the ecological function and evolutionary trajectories of key Antarctic marine bacteria, their genomes will be isolated and sequenced. Then, these genomes will be used to improve the predictions of the paprica metabolic inference pipeline, and our understanding of the relationship between heterotrophic bacteria and their major predators in the Antarctic marine environment. Finally, researchers will modify the Regional Test-Bed Model model to enable microbial diversity data to be used to optimize the starting conditions of key parameters, and to constrain the model's data assimilation methods. There is an extensive education and outreach component to this project that is designed to engage students and the public in diverse activities centered on Antarctic microbiota and marine sciences. A new module on Antarctic marine science will be developed for the popular Sally Ride Science program, and two existing undergraduate courses at UC San Diego will be strengthened with laboratory modules introducing emerging technology, and with cutting-edge polar science. A PhD student and a post-doctoral researcher will be supported by this project.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.