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。硅藻产生特殊的细胞壁材料--方解石球藻和硅藻，是全球生物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。人们普遍认为球石中的钙化是通过与硅藻中的硅化作用非常不同的过程进行的，然而，一些生态上重要的球石谱系拥有类似硅藻的硅(Si)运输系统，并且在球石形成过程中对硅有绝对的需求。重要的是，大量的形成水华的球藻，如玉米草，对硅没有需求。显然有必要了解这些不同的对溶解硅的生理需求是如何驱动球藻生物体的生态和进化的。该项目将更全面地了解球藻石团对硅的需求，它在钙化过程中的作用，以及硅的有效性对这些形成水华的重要浮游植物的生物地理的影响。预计这些结果将加强我们预测球藻生物对短期和长期环境变化的反应的能力，从而预测它们所参与的海洋生物地球化学循环的后果。除了科学成果，该项目还为不同类型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。通过参与者参与区域科学节、公共宣传活动、编写教育资源和有针对性的K-12夏令营活动，促进了公众参与研究。球藻中的钙化似乎代表了与硅藻中硅化不同的过程，硅藻是另一种主要的生物矿化浮游植物。球藻中显然不需要硅(Si)，这一点被认为对它们在溶解硅利用率低的地区击败原本占主导地位的硅藻的能力起到了关键作用。然而，研究人员最近证明，一些全球重要的球藻基团具有硅藻样的硅转运体，并在钙化过程中对硅表现出专有的需求。这一发现对浮游植物生态学和生物矿化演化都具有重要意义。利用一系列生理学、分子和计算方法，该项目将1)确定具有生态重要性的球石生物群的硅需求；2)确定硅在球石生物群中的生理作用；3)确定导致钙化过程中对硅的不同需求的进化事件；4)研究需要硅的球石生物的生态分布；以及5)确定硅需求对球石生物生态的影响。因此，该项目整合了基因(硅转运体)的分子鉴定、这些转运体的生理作用和生态系统规模模型，以研究对硅的需求如何影响生态系统功能和球虫生物地理学。这项工作的结果提供了基本的数据，描述了钙化的细胞机制和主要球石菌谱系之间的生理多样性范围。这项研究还探索了浮游植物生态以前没有预见到的一个方面；研究了钙化球藻对硅的不同要求如何在当代和进化时间尺度上形成了与其他浮游植物的竞争性相互作用。总体而言，这项研究为球虫的生理学、生态学和进化提供了新的见解，包括关于球虫是如何以及为什么产生的信息，这一点目前知之甚少。这一信息对于了解地球气候过去的变化如何影响球藻生物群，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.