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

硅藻占海洋初级生产力的很大一部分。它们与增强的碳出口有关，通常在高营养、低叶绿素(HNLC)地区，它们主导浮游植物对添加微量营养素铁的反应。硅藻，特别是那些从开阔海洋中分离出来的硅藻，似乎有很大的能力储存铁供以后使用，在某些硅藻群体中，这种能力是由铁储存蛋白铁蛋白实现的。这种对铁的奢侈吸收在实验室培养中一直被观察到，并被认为是为了在覆盖全球海洋40%的低铁水域为硅藻提供生态效益。然而，由于处理混合浮游生物组合的方法学挑战，很难在自然系统中观察到铁的储存，而且缺乏对铁对海洋硅藻影响的生理学了解。该项目将最先进的高通量转录测序和单细胞元素分析与新颖的实验室和野外培养实验相结合，以量化含有或不含有铁蛋白的培养和天然硅藻的铁储存能力，并确定这一过程的生态影响。该项目的总体目标是审查铁储存作为一种选择性机制控制海洋生态系统中沿铁梯度分布的硅藻的生态重要性。拟议的研究包括三个具体目标：a.确定羽状硅藻和中心型硅藻储存铁的能力是否存在一致的生理差异；b.检验不同硅藻类群的铁储存能力是否一致地为缺铁情况下的持续生长提供机制解释；c.确定增强的铁储存是否为硅藻在沿海和海洋地区的自然浮游植物组合中提供了竞争优势。将利用对各种具有生态重要性的羽状硅藻和中心型硅藻进行的转录测序来调查是否存在类似铁蛋白的基因，以建立硅藻铁蛋白出现的生物地理和/或系统发生模式。实验室培养实验将被用来量化这些硅藻的铁存储能力，以及存储的铁可以支持的细胞分裂的数量，为了解铁有限的海岸和HNLC系统的浮游生物生态提供有价值的生理数据。实验室实验将通过测量沿海和海洋硅藻中铁蛋白的表达和铁储量的测量来补充，这些样品是在东北太平洋的两次机会巡航中跨铁可获得性梯度采样的。智力价值：通过表征硅藻潜在铁储存能力的多样性，并阐明铁质在加强铁储存和铁限制反应中的作用，该项目将提供新的见解，了解这一重要的初级生产者群体如何适应它们的环境，从而有助于我们了解什么因素影响它们的丰度和分布。这方面的知识对于预测气候变化对这些生物的未来影响尤其重要，这些生物对海洋生态系统中的大量初级生产负有责任。广泛影响：该项目包括几项将直接有助于教育和培训的活动。直接支持培养一名研究生、博士后研究员和多名本科生。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，促进与海洋科学有关的主题的教与学。为了实现这一点，一名高中教师将参加其中一次航海，向她的学生传达她的海上经历，并为她的班级开发课程材料。这些材料将用于高中的地球和环境科学课程，并作为毕格罗实验室教师培训计划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.