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。目前的生态模型识别出能够收获光能并产生有机物质的微生物，以及能够仅从先前产生的有机物质中获得碳和能量的其他微生物。然而，新的数据表明，能够利用光和溶解有机物质（DOM）的光合异养微生物在水生系统中比以前认为的更普遍。本研究的目的是获得淡水水体中光合异养微生物丰度的定量数据，以揭示其生态学意义和生物地球化学作用。该项目将重点关注三种类型的微生物。蓝藻对淡水生态系统的影响是众所周知的，但他们的光合异养作用在很大程度上被忽视。第二种类型的光异养生物，好氧无氧光养（AAP）细菌，已在实验室实验中使用培养菌株进行了研究，但对淡水中AAP细菌的生态学一无所知。第三种具有蛋白视紫质（PR）的光异养生物甚至还没有在湖泊中进行过研究，尽管有证据表明大约一半的海洋原核生物含有PR。该项目将应用一套独特的分析工具，包括流式细胞术，荧光显微镜和环境基因组学，用于研究魁北克南部湖泊中的光异养生物，蒙特利尔北部的劳伦地区和魁北克北方针叶林地区的北方湖泊。这些湖泊在几个不同的环境属性（如营养状态，DOC浓度，颜色和浊度），假设影响光合异养丰度。这项工作将检验光合异养微生物的群落动态和环境控制的假设，这些假设可能对淡水中的生物地球化学过程产生独特的影响。这项工作意义重大，因为它将有助于了解微生物的地理分布，而这些分布现在似乎遵循以前认为只适用于高等生物的生态学原理。这项工作将有助于理解光合异养生物的地理模式，什么环境条件控制它们的丰度和多样性，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，并将对特拉华州大学（刘易斯，DE）海洋与地球研究学院的NSF REU计划产生积极影响。来自林肯大学，美国最古老的历史黑人学院的学生，也将参加另一个NSF支持的计划的一部分。与来自加拿大的游客的互动将丰富暑期实习生和研究生的整体经验。科特雷尔博士的研究结果在刘易斯设施的每周图尔斯参观（每年约1000名游客）和海岸日期间展出，海岸日是每年一次的开放日，吸引了约10,000名游客。该项目的网站将有助于教育有关光合异养微生物的同事和一般公众关于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.