Carbon and Nitrogen acquisition and cycling in heterotrophic and mixotrophic ciliates

在过去的四分之一个世纪里，在理解真核和原核微生物在海洋生态中的作用方面取得了很大进展。通过将实验技术应用于现场自然微生物群落，已经取得了很大的进展。然而，随着我们更多地了解不同个体物种的独特生理和行为特征，特别是纤毛虫和甲藻分支中的真核微生物，有必要进行传统的分离、培养和实验，以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广泛存在的混合营养现象，研究人员认为，研究特定物种中摄食、光合作用和C、N循环之间的联系是很重要的，这些物种已知在数量上重要，并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利用氮和碳有关的假设的实验测试，以评估四个物种(Strombiinopsis sp.、Laboea strobila、Strombidium Styllifer和Mesoddium rubrum)对溶解无机(DIN)和有机氮源的利用，这些物种的碳代谢范围从严格的异养到几乎严格的自养。研究人员还将测量这些纤毛虫的同化和生长效率(对于C和N)，并量化食物和光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作用之间溶解无机碳(DIC)循环的程度，并评估哪些因素控制DIN和DIC的循环和排泄。实验方法将使用15N和14C同位素作为示踪剂，并采用脉冲/追赶设计来分别测量实验室分离株对N和C的吸收和排泄。这一提议的更广泛影响包括培训研究生和一名博士后，以及与K-12教育工作者进行外联。此外，该项目产生的数据将通过互联网和出版物提供。

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.