EAGER: Assessment of Pseudo-nitzschia ferritin gene expression as a molecular indicator of iron nutritional status along natural iron gradients

铁的供应限制了世界上30%-40%的海洋的生产力。在这些地区生存的微生物必须能够在铁可用时迅速吸收和储存铁，并承受有限的铁供应的长时间间隔。铁蛋白是一种高度专门化的铁储存蛋白，存在于许多动物、植物和微生物中。研究人员最近发现，海洋羽状硅藻含有铁蛋白，并表明在海洋和沿海物种中，铁的可获得性与铁蛋白转录丰度直接相关。全基因组序列分析表明，铁蛋白不存在于中心种中，海链藻和大洋种比海洋种海链藻经历了更多的基于储存铁的细胞分裂。基于这些结果，研究人员推测，在间歇性铁输入的低铁环境中，通过铁蛋白增加铁存储提供了相对于羽状硅藻的竞争优势，铁蛋白的活动奠定了它们在海洋铁肥料实验中的主导地位。该项目依靠现场和实验室样本的组合来检验铁蛋白基因(FTN)转录丰度反映硅藻伪硝化藻自然群落铁状态的假设。首先，他们将利用从天然铁梯度和铁生长微宇宙实验中收集的野外样本，该实验在一个铁限制区--帕帕海洋站--进行。格兰氏假单胞菌在所有采样点以及铁诱导的水华中都有大量存在，并将作为目标生物。其次，将在受控的实验室条件下对从OSP分离的P.ranii菌株进行研究，以确认FTN的转录丰度受铁营养状况的影响，而不是其他环境参数。这项研究非常适合通过EIGER计划提供支持，因为有可能开发一种新的分子工具来阐明该领域中浮游植物的铁状态，但开展这项研究的时间紧迫且有限。这项研究将作为原则性研究的证据，以验证羽状硅藻铁蛋白和铁储存作为控制这一生态重要类群分布的选择性机制的重要性。研究的结果将是开发出假菱形藻铁蛋白指数(PFI)，可供其他对评估天然混合浮游植物群落的铁营养状况感兴趣的研究小组使用。铁的测量因现场样品中复杂的铁存在的化合物的多样性而变得复杂，这可能会降低铁的生物有效性。该指数的开发将避免这些潜在的并发症，并将作为铁可获得性的生物学相关指标。每年，六到七名本科生都会有机会在Armbrust实验室进行研究。Marchetti博士是一名早期的职业科学家，他将继续指导一名本科生来帮助这个项目。所有本科生都有机会在每年在华盛顿大学举行的年度本科生研究研讨会上展示他们的研究成果。

Iron availability limits productivity in 30-40% of the world's oceans. Microbes that persist in these regions must be able to rapidly take up and store iron when it is available and withstand long intervals of limited iron supply. Ferritins are highly specialized iron storage proteins present in many animals, plants and microorganisms. The investigators recently discovered that marine pennate diatoms possess ferritin and showed that iron availability was directly related to ferritin transcript abundance in both oceanic and coastal species of the cosmopolitan pennate diatom genus Pseudonitzschia. Whole genome sequence analysis indicated that ferritin is not present within the centric species, Thalassiosira pseudonana and the oceanic species P. granii underwent more cell divisions based on stored iron than an oceanic species of Thalassiosira. Based on these results, the investigators hypothesized that increased iron storage via ferritin provides a competitive advantage to pennate diatoms in low-iron environments that receive intermittent iron inputs and that the activity of ferritin underlies their dominance in oceanic iron fertilization experiments. This project relies on a combination of field and laboratory samples to test the hypothesis that transcript abundance of the ferritin gene (FTN) reflects the iron status of natural communities of the diatom Pseudonitzschia. First, they will utilize field samples collected from a natural iron gradien and from an iron grow-out microcosm experiment at a well-characterized iron-limited region, Ocean Station Papa. P. granii was abundant at all sampled sites, as well as in the iron-induced bloom and will serve as the target organism. Second, P. granii strains isolated from OSP will be investigated under controlled laboratory conditions to confirm that the transcript abundance of FTN is influenced by iron nutritional status and not other environmental parameters. This research is a good fit for support through the EAGER program as there is the potential for the development of a new molecular tool to elucidate the iron status of phytoplankton in the field but there is an urgent and limited time frame in which this research can be performed. The research will serve as a proof of principle study to verify the importance of pennate diatom ferritin and iron storage as a selective mechanism controlling the distributions of this ecologically important group.The outcome of the research will be development of a Pseudonitzschia Ferritin Index (PFI) that can be used by other research groups interested in assessing the iron nutritional status of natural mixed phytoplankton communities. Iron measurements are complicated by the diversity of compounds that complex iron present within field samples, potentially lowering the biological availability of iron. Development of the index will obviate these potential complications and would serve as a biologically relevant indicator of iron availability. Each year, six to seven undergraduates are given opportunities to conduct research in the Armbrust lab. Dr. Marchetti, an early career scientist, will continue to mentor an undergraduate to help with this project. All undergraduates have the opportunity to present their research at the Annual Undergraduate Research Symposium held each year at the University of Washington.