Significance of metabolic interactions of diatom-diazotrophic associations (DDAs) for ocean ecosystems

硅藻(即半毛藻)与异晶蓝藻(即黎氏藻)共生，被认为对世界海洋中很大比例的双氮(N_2)和碳(C)的固定负责。尽管这些组合经常形成大规模的水华，但它们固定氮和碳的指标很少，而且目前的氮(N)和碳预算模型不包括它们对新的和初级生产的贡献。这在很大程度上是因为难以收集和识别这些独特的财团。研究人员将使用新开发的遗传和稳定同位素技术以及高分辨率纳米级二次离子质谱仪(NanSIMS)方法，在相关的空间尺度上直接解析这些共生硅藻对氮(和碳)的固定贡献。该项目将使研究人员能够探索硅藻-地那托普共生体的代谢相互作用，并确定促进一个共生体相对于另一个共生体活动的环境条件。推动这项研究的三个一般性问题是：1)单个硅藻-蓝藻共生体在细胞特定的氮和碳固定率方面有何不同；2)N从共生体转移到宿主的时间尺度是什么；3)促进不同共生体活性的物理和化学条件是什么。这项研究的更广泛影响包括提高我们对海洋微生物之间代谢相互作用的知识，并提供对海洋浮游共生生物更好的理解。此外，该项目还将有助于建立一个用于教育宣传的网上照片资料库。此外，它还将支持本科生高级论文项目的培训和教育，并将促进我们对海洋微生物活动的了解。

Diatoms (i.e., Hemiaulus) with symbiotic heterocystous cyanobacteria (i.e., Richelia) are considered responsible for a significant proportion of di-nitrogen (N2) and carbon (C) fixation in the World's oceans. Although these associations often form large and expansive blooms, measures of their N2 and C fixation are few, and current nitrogen (N) and C budget models do not include their contributions to new and primary production. This is largely due to the difficulty in collection and identification of these unique consortia. The investigators will use newly developed genetic and stable isotope techniques and high resolution nanometer-scale secondary ion mass spectrometry (nanoSIMS) approaches to directly resolve the N2 (and C) fixation contributions of these symbiotic diatoms on a relevant spatial scale.The project will enable investigators to explore the metabolic interactions of diatom-diazatoph symbioses and identify environmental conditions that promote the activity of one symbiosis over the other. The three general questions driving the research are: 1) How do the individual diatom-cyanobacteria symbioses differ with respect to their cell specific N2 and C fixation rates; 2) What is the time scale at which N is transferred from symbiont to host; 3) What are the physical and chemical conditions that promote the activity of the different symbioses. The broader impacts of the research involve advancing our knowledge of metabolic interactions between marine microorganisms, and providing a better understanding of marine planktonic symbioses. In addition, the project will contribute to an on-line web library of photographs for educational outreach. Furthermore, it will support training and education to an undergraduate senior thesis project, and will advance our knowledge of the activity of marine microorganisms.