COLLABORATIVE RESEARCH: Combining Flow Cytometry and Stable Isotope Techniques: A Method to Measure Phytoplankton- and Bacteria-specific Nitrogen and Carbon Uptake

多种证据挑战了传统观点，即浮游植物是水生微生物群落的生产者，细菌是消费者，这种观点过于简单化或不正确。以前归因于一种微生物或官能团的许多营养策略也由其他微生物组执行或取而代之。在该项目中，研究人员将使用新开发的分析方法来重新评估浮游植物和细菌在海洋生态系统中的功能作用。传统上，氮(N)的吸收速率是使用15N示踪技术测量的，这种技术使用了玻璃纤维过滤器(即GF/F)。然而，很少有人意识到，细菌群落的很大一部分和可变部分被保留在这些过滤器上。因此，通常被认为代表自养生产的摄取率实际上与异养细菌摄取混淆。当与其他技术相结合时，流式细胞术在扩大我们对竞争相互作用的理解方面具有巨大的潜力，而且在很大程度上尚未开发，因为微生物群可以通过光学(通过固有的荧光团，如颜料或通过使用荧光染料)来区分，进行分类，然后收集用于特定的分析。研究人员将培养和实地研究相结合，以完成一种耦合的流式细胞仪分选-稳定同位素方法的开发，以实现以下目标：量化浮游植物特有的氮和碳(C)吸收速率。量化细菌特定的N和C摄取率。开展小型试验性野外研究，展示该方法在两个系统--富营养化的切萨皮克湾和低营养的马尾藻海--中的应用。开发一种可靠的方法来量化特定于浮游植物和特定于细菌的N和C吸收速率，将产生深远的影响。进一步量化特定于分类群的吸收速率的能力(例如硅藻与甲藻和古细菌)有可能改变我们对海洋环境中N和C生物地球化学的理解。此外，该项目还包括为本科生和研究生提供培训机会。

Multiple lines of evidence challenge the traditional view that phytoplankton are producers and bacteria are consumers in aquatic microbial communities as overly simplistic or incorrect. Many nutritional strategies previously attributed to one microorganism or functional groups are also or instead carried out by other groups of microorganisms. In the project, the investigators will use newly developed analytical approaches to reassess the functional roles of phytoplankton and bacteria in marine ecosystems. Traditionally nitrogen (N) uptake rates have been measured using 15N-tracer techniques that employ glass fiber filters (i.e. GF/Fs). What is seldom appreciated, however, is that a significant and variable fraction of the bacterial community is retained on these filters. As a result, uptake rates that are frequently assumed to represent autotrophic production are in fact confounded with heterotrophic bacterial uptake. Flow cytometry, when combined with other techniques, has a great, and largely untapped, potential for expanding our understanding of competitive interactions because microbial groups can be distinguished optically (either by inherent fluorophores such as pigments or by using fluorescent stains), sorted, and then collected for specific analyses. The investigators will combine culture and field study to complete the development of a coupled flow cytometric sorting - stable isotope method that to accomplish the following objectives:. Quantify the rate of phytoplankton-specific N and carbon (C) uptake. Quantify the rate of bacteria-specific N and C uptake. Conduct a small pilot field study to show the utility of the method in two systems the eutrophic Chesapeake Bay and the oligotrophic Sargasso Sea.The broader impacts will be far reaching by the development of a robust method to quantify phytoplankton-specific and bacteria-specific N and C uptake rates. The ability to further quantify taxa-specific uptake rates (e.g. diatoms vs. dinoflagellates vs. Archaea) has the potential to transform our understanding of N and C biogeochemistry in the marine environment. In addition, the project includes training opportunities for undergraduate and graduate students.