NSFGEO-NERC: An unexpected requirement for silicon in coccolithophore calcification: physiological, ecological and evolutionary implications

海洋浮游植物的生物矿化作用对我们的星球产生了深远的影响。特殊的细胞壁材料，方解石球石藻和硅藻硅硅藻壳的生产，是全球地球化学循环的主要驱动力，但基本的细胞过程仍然知之甚少。颗石藻的钙化过程与硅藻的硅化过程有很大的不同，但一些生态上重要的颗石藻谱系具有类硅的转运系统，并且在颗石形成过程中对硅有绝对的需求。重要的是，丰富的开花形成颗石藻，如Emiliania huxleyi表现出不需要硅。有一个明确的需要，以了解这些不同的生理需求溶解硅驱动的生态和演化的颗石藻。该项目将产生一个更完整的理解的硅的要求颗石藻，其在钙化过程中的作用，以及硅的可用性对这些重要的水华形成浮游植物的生物地理学的影响。预计这些结果将加强我们预测颗石藻对短期和长期环境变化的反应的能力，从而预测它们参与的海洋生物地球化学循环的后果。 除了科学成果外，该项目还为多样化的本科生提供独立研究机会，为研究生提供跨学科培训，并促进博士后研究人员的专业发展。公众参与的研究是促进通过参与者参与区域科学节，公众宣传活动，教育资源的生产，并有针对性的K-12夏令营activities.Calcification颗石藻似乎代表了一个不同的过程中硅化硅藻，另一个主要的生物矿化浮游植物。在颗石藻中明显不需要硅（Si），这被认为是它们在低溶解硅可用性地区竞争优势硅藻的能力中发挥关键作用的原因。然而，研究人员最近证明，一些全球重要的颗石藻拥有类钙离子硅转运蛋白，并表现出在钙化过程中对硅的强制性需求。这一发现对浮游植物生态学和生物矿化的演化都具有重要意义。利用一系列生理、分子和计算方法，该项目将1）建立生态上重要的颗石藻群对硅的需求; 2）确定硅在颗石藻中的生理作用; 3）确定导致钙化对硅的不同需求的进化事件;（4）研究需硅颗石藻的生态分布;（5）确定硅需求对颗石藻生态的影响。因此，该项目整合了基因（硅转运蛋白）的分子鉴定，这些转运蛋白的生理作用，以及生态系统规模的模型，以研究硅的需求如何影响生态系统功能和颗石藻地理。这项工作的结果提供了必要的数据，描述了钙化的细胞机制和主要的颗石细胞谱系之间的生理多样性的范围。该研究还探索了浮游植物生态学以前未预见的方面;研究了钙化颗石藻对Si的不同需求如何在当代和进化时间尺度上形成与其他浮游植物的竞争性相互作用。总的来说，这项研究为颗石藻的生理学、生态学和进化提供了新的见解，包括关于颗石藻是如何产生的以及为什么产生的信息，目前对此知之甚少。这些信息对于了解颗石藻如何受到地球气候过去变化的影响以及它们对未来海洋的潜在反应至关重要。

Biomineralization by marine phytoplankton has had a profound impact on our planet. The production of special cell wall material, calcite coccoliths by coccolithophores and silica frustules by diatoms, are major drivers in global biogeochemical cycles, but the underlying cellular processes remain poorly understood. It is widely considered that calcification in coccolithophores occurs through a very different process to silicification in diatoms, however some ecologically important coccolithophore lineages possess diatom-like silicon (Si) transport systems and have an absolute requirement for Si during coccolith formation. Importantly, the abundant bloom-forming coccolithophores such as Emiliania huxleyi exhibit no requirement for Si. There is a clear need to understand how these different physiological requirements for dissolved Si have driven the ecology and evolution of the coccolithophores. The project will yield a more complete understanding of the Si requirements of coccolithophores, its role in the calcification process, and the impacts of Si availability on the biogeography of these important bloom forming phytoplankton. The results are expected to strengthen our ability to predict the responses of coccolithophores to short and long-term environmental change, and therefore the consequences for the marine biogeochemical cycles in which they participate. In addition to the scientific outcomes, the project provides independent research opportunities to a diverse pool of undergraduate students, provide interdisciplinary training for graduate students, and facilitate the professional development of post-doctoral researchers. Public engagement in the research is facilitated through participant involvement in regional science festivals, public outreach events, production of educational resources, and targeted K-12 summer camp activities.Calcification in coccolithophores appears to represent a distinct process from silicification in diatoms, another major group of biomineralized phytoplankton. The apparent absence of a requirement for silicon (Si) in coccolithophores has been proposed to play a critical role in their ability to out-compete the otherwise dominant diatoms in areas of low dissolved Si availability. However, the investigators recently demonstrated that some globally important coccolithophores possess diatom-like Si transporters and exhibit an obligate requirement for Si in the calcification process. This discovery has important implications both for phytoplankton ecology and for the evolution of biomineralization. Using a range of physiological, molecular and computational approaches the project will 1) Establish Si requirements of ecologically important coccolithophore groups; 2) Determine the physiological role of Si in coccolithophores; 3) Determine the evolutionary events leading to the differing requirements for Si in calcification; 4) Examine the ecological distribution of Si-requiring coccolithophores, and 5) Determine the impact of the Si requirement on coccolithophore ecology. This project therefore integrates the molecular identification of genes (Si transporters), the physiological role of these transporters, and ecosystem scale models in order to examine how the requirement for Si influences ecosystem functioning and coccolithophore biogeography. The results of this work provides essential data that describes the cellular mechanisms of calcification and the range of physiological diversity between major coccolithophore lineages. The research also explores a previously unforeseen aspect of phytoplankton ecology; examining how the differing requirements for Si in calcifying coccolithophores may have shaped competitive interactions with other phytoplankton over both contemporary and evolutionary timescales. Overall, the research provides novel insights into physiology, ecology and evolution of coccolithophores, including information on how and why coccoliths are produced, which is currently poorly understood. This information is vital in order to understand how coccolithophores have been influenced by past changes in the Earth's climate, and their potential responses to future oceans.