Carbon and Nitrogen acquisition and cycling in heterotrophic and mixotrophic ciliates

在过去的四分之一世纪里，人们对海洋生态学中真核微生物和原核微生物作用的认识取得了很大进展。大量的这方面的进展已经取得了应用实验技术的天然微生物群落在原位。然而，随着我们对不同物种的独特生理和行为特征的了解，特别是纤毛虫和甲藻分支中的真核微生物，需要传统的分离，培养和实验来阐明不同物种的代谢潜力和生态作用。鉴于微生物真核生物中混合营养的广泛存在，研究人员认为，重要的是要检查特定物种的摄食，光合作用和C和N循环之间的联系，这些物种在数量上是重要的，并且在全球范围内广泛分布。因此，研究人员开发了与浮游纤毛虫使用氮和碳有关的假设的实验测试，以评估四种纤毛虫（Strombidinopsis sp.，它们的碳代谢从严格的异养到近乎严格的自养。研究人员还将测量这些纤毛虫的同化和生长效率（C和N），并量化食物和光线在氮排泄和内部循环中的作用。对于这三种混合营养形式，研究人员将测量光合作用和呼吸之间溶解无机碳（DIC）循环的程度，并评估哪些因素控制DIN和DIC的再循环与排泄。实验方法将使用15 N和14 C同位素作为示踪剂，并采用脉冲/追踪设计，分别测量实验室分离株中N和C的摄取和排泄。这项建议的更广泛的影响包括培训研究生和一名博士后，以及推广到K-12教育工作者。 此外，将通过互联网和出版物提供该项目产生的数据。

Much progress has been made in the last quarter century in understanding the roles of both eukaryotic and prokaryotic microbes in the ecology of the ocean. A good deal of this progress has been made by the application of experimental techniques to natural microbial communities in situ. However, as we learn more about the unique physiological and behavioral features of different individual species, especially of eukaryotic microbes in the ciliate and dinoflagellate clades, there is a need for traditional isolation, cultivation, and experimentation to clarify metabolic potential and ecological roles of different species. Given the widespread occurrence of mixotrophy among microbial eukaryotes, the investigators believe it is important to examine the connections between feeding, photosynthesis, and C and N cycling in particular species that are known to be quantitatively important and widely distributed globally. As a result, the investigators have developed experimental tests of hypotheses related to the use of nitrogen and carbon by planktonic ciliates to evaluate the use of dissolved inorganic (DIN) and organic nitrogen sources in four species (Strombidinopsis sp., Laboea strobila, Strombidium stylifer, and Mesodinium rubrum) whose carbon metabolisms range from strict heterotrophy to near-strict autotrophy. The investigators will also measure assimilation and growth efficiencies of these ciliates (for both C and N) and quantify the role of food and light in nitrogen excretion and internal cycling. For the three mixotrophic forms, the investigators will measure the extent of dissolved inorganic carbon (DIC) cycling between photosynthesis and respiration and evaluate what factors control recycling vs excretion of DIN and DIC. The experimental approach will be to use 15N and 14C isotopes as tracers and to employ a pulse/chase design to measure separately the uptake and excretion of N and C in laboratory isolates. The broader impacts of this proposal include training of graduate students and one post-doc as well as outreach to K-12 educators. In addition, data resulting from this project will be made available through the internet as well as in publications.