Collaborative Research: Biology and phylogeny of marine planktonic cyanobacterial symbioses

我们建议对赤道营养不良的大西洋和太平洋蓝藻与浮游硅藻、甲藻、放射虫、硅鞭毛藻和其他浮游原生动物之间的共生进行研究。我们最近观察到，这些共生体是多样和丰富的，其中一些尚未在科学文献中报道。这些共生体的生物学和系统发育几乎没有人研究过。蓝藻共生体的16S rDNA序列分析表明，它们与蓝藻属的共生体(在夜间固定)关系密切，这表明其中一些共生体可能与固氮作用有关。我们推测，蓝藻共生体可能通过结合固定的N或C(通过DON或DOC的释放或被吞噬)而有益于宿主物种。该研究方法将使用显微镜和分子生物学相结合的方法，将观察到的蓝藻和真核微藻之间的关系与系统发育信息和涉及固氮的基因检测联系起来。利用直接通过显微镜采集的样品和大量过滤的水样，固氮基因的特性、固氮潜力(存在固氮酶基因)和固氮基因的表达将与特定的生物相关并在水柱中被量化。这些方法将基于从共生体中扩增和测序16S rDNA以了解蓝藻的系统发育，检测nifH的存在作为固定氮气能力的指标，检查宿主和蓝藻的超微结构，使用14C放射自显影技术检查碳转移，测量丰度和分布以量化生态重要性，以及培养尝试允许实验室研究，旨在利用GC/MS确定共生相互作用的性质。拟议的研究将利用未来三年在大西洋和太平洋计划的四次已获资助的(NSF)研究巡航。

We propose a study of symbioses between cyanobacteria and planktonic diatoms, dinoflagellates, radiolarians, silicoflagellates and other planktonic protozoans in the equatorial oligotrophic Atlantic and Pacific Oceans. We have recently observed that these symbioses are diverse and abundant, and some have not yet been reported in the scientific literature. The biology and the phylogeny of these symbioses are virtually unstudied. The 16S rDNA sequences of cyanobacterial symbionts within a diatom (Climacodium) showed that they are closely related to the N2 fixing genus Cyanothece (which fixes during the night), which suggests that some of these symbioses may involve N2 fixation.We hypothesize that cyanelle symbionts may benefit host species either via incorporation of fixed N or C (via DON or DOC release or by being phagocyticized). The research approach will use combined microscopy and molecular biology approaches to link observed relationships between cyanobacteria and the eukaryotic microalgae with phylogenetic information and detection of the genes involved in nitrogen fixation. Using samples collected directly by microscopy, and bulk filtered water samples, the identity, nitrogen fixation potential (presence of nitrogenase genes) and expression of nitrogen fixation genes will be related to specific organisms and quantified in the water column. These approaches will be based on amplification and sequencing of 16S rDNA from the symbionts to understand the phylogeny of the cyanobacteria, and detection of the presence of nifH as an indicator of capacity to fix N2, examination of the ultrastructure of host and cyanelle, use of 14 C autoradiography to examine C transfer, measurements of abundance and distribution to quantify ecological importance, along with culture attempts to allow laboratory studies directed at determining the nature of the symbiotic interactions using GC/MS. The proposed research will take advantage of four already- funded (NSF) research cruises scheduled over the next three years in the Atlantic and Pacific Oceans.