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

在水生微生物群落中，浮游植物是生产者，细菌是消费者的传统观点过于简单化或不正确，多种证据对这种观点提出了挑战。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群执行或代替。在该项目中，研究人员将使用新开发的分析方法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)吸收率是使用15n示踪技术测量的，该技术采用玻璃纤维过滤器（即GF/Fs）。然而，很少有人意识到的是，这些过滤器上保留了细菌群落的重要和可变部分。因此，通常被认为代表自养生产的摄取速率实际上与异养细菌的摄取相混淆。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很大的潜力，而且在很大程度上尚未开发，因为微生物群可以光学地区分（通过固有的荧光团，如色素或通过使用荧光染色），分类，然后收集用于特定分析。研究人员将结合培养和实地研究来完成一种耦合的流式细胞分选-稳定同位素方法的开发，以实现以下目标：量化浮游植物对氮和碳(C)的吸收率。量化细菌特异性氮和碳的吸收率。进行小型试点实地研究，以证明该方法在富营养化切萨皮克湾和贫营养化马尾藻海两个系统中的效用。通过开发一种量化浮游植物特异性和细菌特异性氮和碳吸收率的可靠方法，将产生深远的广泛影响。进一步量化特定物种的吸收率（例如硅藻、鞭毛藻和古细菌）的能力有可能改变我们对海洋环境中氮和碳生物地球化学的理解。此外，该项目还包括本科生和研究生的培训机会。

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.