Collaborative Research: Investigating the Ecological Importance of Iron Storage in Diatoms

硅藻在海洋初级生产中占很大比例。它们与碳输出增强有关，并且通常主导浮游植物对高营养低叶绿素（HNLC）区域微量营养素铁添加的响应。硅藻，特别是那些从开放海洋中分离出来的硅藻，似乎具有储存铁供以后使用的重要能力，在某些硅藻群中，这种能力是由铁蛋白储存铁蛋白实现的。长期以来，在实验室培养中观察到这种对铁的奢侈吸收，并假设硅藻在覆盖全球海洋40%的低铁水域中具有生态效益。然而，由于研究混合浮游生物组合的方法挑战，铁的储存在自然系统中很难观察到，并且缺乏对铁对海洋硅藻影响的生理学理解。该项目将最先进的高通量转录组测序和单细胞元素分析与新颖的实验室和现场孵化实验相结合，量化培养和天然硅藻含或缺乏铁蛋白的铁储存能力，并确定这一过程的生态影响。该项目的总体目标是研究铁储存作为控制海洋生态系统中硅藻沿铁梯度分布的选择机制的生态重要性。拟议的研究包括三个具体目标：A；确定pennate和centric硅藻储存铁的能力是否存在一致的生理差异。研究不同硅藻类群的铁储存能力是否一致地为在缺乏铁的情况下持续生长提供了机制解释。确定加强铁储存是否使硅藻在沿海和海洋地区的天然浮游植物组合中具有竞争力。对多种生态上重要的pennate和centric硅藻的转录组测序将用于调查铁蛋白样基因的存在，以建立硅藻铁蛋白发生的生物地理和/或系统发育模式。实验室培养实验将用于量化这些硅藻的铁储存能力，以及储存的铁可以支持的细胞分裂数量，为了解铁限制的沿海和HNLC系统中的浮游生物生态提供有价值的生理数据。在两次前往东北太平洋的机会巡航中，将对沿海和海洋硅藻的铁蛋白表达和铁储存进行测量，以补充实验室实验。知识价值：通过表征硅藻潜在储铁能力的多样性，阐明铁蛋白在增强铁储存和铁限制反应中的作用，该项目将为这一重要的初级生产者群体如何适应其环境提供新的见解，从而有助于我们了解影响其丰度和分布的因素。这方面的知识对于预测气候变化对这些负责海洋生态系统重要初级生产的生物的未来影响尤其重要。更广泛的影响：该项目包含了几项将直接促进教育和培训的活动。直接支持培养1名研究生、博士后和多名本科生。此外，该项目的一个更广泛的影响目标是通过将我们的研究目标转化为可在课堂上使用的广泛分发的教育材料，促进海洋科学相关主题的教学。为了实现这一目标，一名高中教师将参加其中一艘游轮，向她的学生传达她在海上的经历，并为她的班级开发课程材料。这些教材将用于高中地球和环境科学课程，并作为毕格罗实验室教师培训方案的一部分分发给缅因州的教师，从而扩大了外联活动的范围。

Diatoms are responsible for a significant fraction of primary production in the ocean. They are associated with enhanced carbon export and usually dominate the response of phytoplankton to additions of the micronutrient iron in high-nutrient, low-chlorophyll (HNLC) regions. Diatoms, particularly those isolated from the open ocean, appear to have a significant capacity to store iron for later use, and in some groups of diatoms this ability is enabled by the iron storage protein ferritin. Such luxury uptake of iron has long been observed in laboratory cultures and hypothesized to provide diatoms with an ecological benefit in the low-iron waters that cover 40% of the global ocean. However iron storage has been difficult to observe in natural systems due to the methodological challenges of working with mixed plankton assemblages, and a physiological understanding of the impacts of iron on ocean diatoms is lacking. This project combines state-of-the-art high-throughput transcriptomic sequencing and single-cell element analysis with novel laboratory and field incubation experiments to quantify iron storage abilities of cultured and natural diatoms that either contain or lack ferritin and determine the ecological impacts of this process. The overall objective of this project is to examine the ecological importance of iron storage as a selective mechanism controlling the distributions of diatoms along iron gradients in marine ecosystems. The proposed research includes three specific objectives:A. Determine if there is a consistent physiological difference in the ability of pennate versus centric diatoms to store iron.B. Examine whether iron storage capacities across diverse diatom taxa consistently provide a mechanistic explanation for continued growth in the absence of iron.C. Determine whether enhanced iron storage provides diatoms with a competitive within natural phytoplankton assemblages in both coastal and oceanic regions.Transcriptomic sequencing on a variety of ecologically important pennate and centric diatoms will be used to survey for the presence of ferritin-like genes in order to establish biogeographical and/or phylogenetic patterns of occurrence of diatom ferritin. Laboratory culture experiments will be used to quantify the iron storage abilities of these diatoms, as well as the number of cell divisions that can be supported by the stored iron, providing valuable physiological data to inform the understanding of plankton ecology in iron-limited coastal and HNLC systems. The laboratory experiments will be complemented by measurements of ferritin expression and iron storage in coastal and ocean diatoms sampled across gradients of iron availability on two cruises-of-opportunity to the northeast Pacific Ocean.Intellectual Merit: By characterizing the diversity in potential iron storage capacities of diatoms and elucidating the role ferritins play in enhancing iron storage and the iron-limitation response, this project will provide new insights into how this important group of primary producers has adapted to their environment, thus contributing to our knowledge of what factors influence their abundance and distributions. This knowledge is especially important in relation to predicting the future effects of climate change on these organisms that are responsible for significant primary production in marine ecosystems.Broader Impacts: This project incorporates several activities that will directly contribute to education and training. The training of a graduate student, post-doctoral researcher and multiple undergraduates will be directly supported. Additionally, a broader impact goal of this project is to facilitate teaching and learning on marine science-related topics through translating our research objectives into widely distributed educational materials that can be used in the classroom. To accomplish this, a high-school teacher will participate in one of the cruises and convey her experiences at sea to her students as well as develop curricular materials for her class. These will be used for high-school earth and environmental science courses and also distributed to teachers in Maine as part of Bigelow Laboratories teacher training program, thus broadening the scope of the outreach activities.