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

铁的可用性限制了世界上30-40%海洋的生产力。在这些地区持续存在的微生物必须能够在铁可用时迅速吸收和储存铁，并承受长时间的有限铁供应。铁蛋白是存在于许多动物、植物和微生物中的高度专门化的铁储存蛋白。研究人员最近发现，海洋pennate硅藻具有铁蛋白，并表明铁的有效性直接关系到铁蛋白转录丰度的海洋和沿海物种的世界性pennate硅藻属Pseudonitzschia。全基因组序列分析表明，在中心种中不存在铁蛋白，假海藻和海洋种P. granii比海洋种进行了更多的基于储存铁的细胞分裂。基于这些结果，研究人员假设，铁蛋白增加的铁储存为在低铁环境中接受间歇性铁输入的pennate硅藻提供了竞争优势，铁蛋白的活性是它们在海洋铁施肥实验中占主导地位的基础。该项目依赖于野外和实验室样品的结合来验证铁蛋白基因（FTN）转录丰度反映假硅藻天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观实验中收集的现场样品，这些样品来自一个特征明显的铁限制地区，海洋站Papa。在所有采样点以及铁诱导的水华中，P. granii都很丰富，并将作为目标生物。其次，将在受控的实验室条件下研究从OSP中分离出来的P. granii菌株，以确认FTN的转录丰度受铁营养状况而非其他环境参数的影响。这项研究很适合通过EAGER计划获得支持，因为有潜力开发一种新的分子工具来阐明该领域浮游植物的铁状态，但这项研究可以进行的时间紧迫且有限。本研究将为验证pennate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机制的重要性提供原理证明。这项研究的结果将是开发一个伪子藻铁蛋白指数（PFI），可以被其他对评估天然混合浮游植物群落铁营养状况感兴趣的研究小组使用。铁的测量由于野外样品中存在的复杂铁化合物的多样性而变得复杂，这可能会降低铁的生物可利用性。该指数的开发将消除这些潜在的并发症，并将作为铁可用性的生物学相关指标。每年，六到七名本科生有机会在Armbrust实验室进行研究。马尔凯蒂博士是一名早期的职业科学家，他将继续指导一名本科生帮助完成这个项目。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。

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.