Microbial photoheterotrophy in lakes: biogeographical patterns, environmental controls and ecological significance

阳光提供了驱动湖泊生态系统生态的大部分能量。目前的生态模型认为微生物能够收集光能并产生有机物质，而其他微生物只能从以前产生的有机物质中获取碳和能量。然而，新的数据表明，能够利用光和溶解有机物质（DOM）的光异养微生物在水生系统中比以前认为的更为普遍。本工作的目的是获得淡水中光异养微生物丰度的定量数据，以揭示其生态意义和生物地球化学作用。该项目将重点研究三种类型的微生物。蓝藻对淡水生态系统的影响是公认的，但它们的光异养作用在很大程度上被忽视了。第二种类型的光异养菌，即需氧无氧光养（AAP）细菌，已经在实验室实验中使用培养菌株进行了检测，但对淡水中AAP细菌的生态学一无所知。尽管有证据表明，大约一半的海洋原核生物含有变形紫质（PR），但第三种光异养生物甚至没有在湖泊中进行过检测。该项目将应用一套独特的分析工具，包括流细胞仪、荧光显微镜和环境基因组学，用于检测quacimbec南部湖泊、蒙特利尔北部劳伦森地区和quacimbec北部太林带地区的北方湖泊中的光异养生物。这些湖泊在一些环境特性（如营养状况、DOC浓度、颜色和浊度）上有所不同，这些特性被认为会影响光异养菌的丰度。这项工作将测试关于光异养微生物群落动态和环境控制的假设，这些微生物可能对淡水生物地球化学过程产生独特的影响。这项工作意义重大，因为它将有助于形成微生物地理分布的新图景，现在看来，微生物的地理分布遵循着以前认为只适用于高等生物的生态原则。这项工作将有助于了解光异养生物的生物地理格局、控制其丰度和多样性的环境条件以及这些微生物在淡水中的潜在生态意义。该项目将支持研究生和本科生以及公众的教育。该项目将直接支持一名研究生的工作，并对特拉华大学海洋与地球研究学院的NSF REU项目产生积极影响。林肯大学是美国历史最悠久的黑人学院，该校的学生也将参加另一个由美国国家科学基金会支持的项目。与加拿大游客的互动将丰富暑期实习生和研究生的整体经验。科特雷尔博士的成果在刘易斯设施的每周参观（每年约有1000名游客）和海岸日期间展出，海岸日每年开放参观，吸引约10,000名游客。该项目的网站将有助于向同事介绍光异养微生物，并向公众介绍微生物在淡水生态系统中的重要性。

Sunlight provides much of the energy that drives the ecology of lake ecosystems. Current ecological models recognize microbes that harvest light energy and generate organic materials and other microbes capable of obtaining carbon and energy only from previously generated organic materials. However, new data suggest that photoheterotrophic microbes capable of using both light and dissolved organic materials (DOM) are more prevalent in aquatic systems than was previously believed. The goal of this work is to obtain quantitative data on the abundances of photoheterotrophic microbes in freshwaters that will reveal their ecological significance and biogeochemical roles. The project will focus on three types of microbes. The impact of cyanobacteria on freshwater ecosystems is well recognized, but their photoheterotrophic role has been largely overlooked. A second type of photoheterotroph, the aerobic anoxygenic phototrophic (AAP) bacteria, has been examined in laboratory experiments using cultured strains, but nothing is known about the ecology of AAP bacteria in freshwaters. A third type of photoheterotroph possessing proteorhodopsin (PR) has not even been examined in lakes, even though evidence indicates that about half of marine prokaryotes contain PR. The project will apply a unique set of analytical tools, including flow cytometry, fluorescence microscopy and environmental genomics for examining photoheterotrophs in the lakes of southern Québec, the Laurentian region north of Montreal and boreal lakes in the taiga regions of northern Québec. These lakes vary in several environmental properties (e.g. trophic status, DOC concentrations, color and turbidity) that are hypothesized to affect photoheterotroph abundance. The proposed work will test hypotheses about community dynamics and environmental controls of photoheterotrophic microbes, which potentially have unique impacts on biogeochemical processes in freshwaters.This work is significant because it will contribute to an emerging picture of the geographical distribution of microbes that now appears to follow ecological principles like those previously thought to apply only to higher organisms. The work will contribute to understanding the biogeographical patterns of photoheterotrophs, what environmental conditions control their abundance and diversity, and the underlying ecological significance of these microbes in freshwaters. This project will support the education of graduate and undergraduate students and the general public. The project will directly support the work of a graduate student and would positively impact the NSF REU program at the College of Marine and Earth Studies at the University of Delaware (Lewes, DE). Students from Lincoln University, the nation's oldest Historical Black College, will also participate as part of another NSF-supported program. Interactions with visitors from Canada will enrich the overall experience of the summer interns and graduate students. Dr. Cottrell's results are featured during weekly tours of Lewes facilities (about 1000 visitors per year) and during Coast Day, an annual open house that attracts about 10,000 visitors. The project's web site will help to educate colleagues about photoheterotrophic microbes and the general public about the importance of microbes in freshwater ecosystems.