Collaborative Research: Biology and phylogeny of marine planktonic cyanobacterial symbioses

我们建议在赤道少营养的大西洋和太平洋研究蓝藻与浮游硅藻、鞭毛藻、放射虫、硅鞭毛藻和其他浮游原生动物的共生关系。我们最近观察到这些共生现象是多样而丰富的，有些还没有在科学文献中报道过。这些共生体的生物学和系统发育几乎没有被研究过。一种硅藻（Climacodium）内的蓝藻共生菌的16S rDNA序列表明它们与固定N2属（在夜间固定）密切相关，这表明其中一些共生菌可能涉及固定N2。我们假设蓝藻共生体可能通过结合固定N或C（通过DON或DOC释放或被吞噬）使宿主物种受益。该研究方法将结合显微镜和分子生物学方法，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参与固氮的基因检测联系起来。利用显微镜直接采集的样品和大量过滤水样，将固氮基因的鉴定、固氮电位（存在的氮酶基因）和表达与特定生物相关，并在水柱中进行量化。这些方法将基于共生体16S rDNA的扩增和测序，以了解蓝藻的系统发育，检测nifH的存在，作为固定N2能力的指标，检查宿主和蓝藻的超微结构，使用14c放射自显影检查C转移，测量丰度和分布，以量化生态重要性。随着培养尝试允许实验室研究直接确定共生相互作用的性质，使用GC/MS。拟议的研究将利用计划在未来三年内在大西洋和太平洋进行的四次已经资助的（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.