NSFGEO-NERC: Collaborative Research: Novel imaging, physiology and numerical approaches for understanding biologically mediated, unsteady sinking in marine diatoms

该项目由美国国家科学基金会地球科学理事会（NSF/GEO）和英国国家环境研究委员会（UKRI/NERC）通过NSF/GEO-NERC牵头机构协议共同资助。该协议允许美国/英国提交一份联合提案，并由其调查员拥有最大比例预算的机构进行同行评审。在成功地共同确定一项奖励后，每个机构为预算的比例和与自己的调查人员有关的调查人员和工作的组成部分提供资金。这个项目采用小规模的方法来观察单个细胞来研究海洋硅藻的下沉，这在更大的尺度上对大型生物的食物、碳和有机颗粒如何在海洋中移动有影响。硅藻是一种浮游植物，这种细胞利用表层水的光合作用产生世界上大约一半的氧气和食物，以支持海洋食物网。它们有一个沉重的、玻璃状的外壁，使它们下沉，并将高达40%的颗粒有机碳从海洋表面转移到深海。研究人员正在使用新颖的方法来确定硅藻是如何根据不同的环境条件快速调节下沉的。其中包括最先进的单个细胞的视频测量，了解细胞表面变化的微电极方法，以及观察细胞内部和表面变化的显微镜。由此产生的信息将用于建立一个模型，以了解硅藻如何以及为什么基于其环境使用不稳定的下沉行为。该项目支持早期职业研究者，为博士后科学家和本科生提供培训，并在美国和英国科学家之间开展合作。该团队还与当地高中合作制定课程计划，这些高中在STEM领域的代表性不足的学生人数很多。硅藻的下沉和悬浮问题由于其生态、进化和生物地球化学意义而受到了相当大的关注，但对调节下沉速率的过程的理解仍处于初级阶段。研究人员利用新技术进行了初步观察，发现某些种类的硅藻表现出一种不稳定的下沉行为，这种下沉行为由浮力在几秒钟内的快速变化组成。然而，目前尚不清楚这种行为在物种和海洋条件下的影响有多广泛。在这项研究中，研究小组正在使用最先进的视频测量单个细胞的下沉速率，以评估不同细胞大小的中心硅藻和pennate硅藻之间不稳定下沉的普遍程度，并量化这种行为如何响应营养和光线的急剧梯度。该项目利用跨学科的国际合作，结合创新的光学技术，先进的工具来评估细胞生理学，以及数值模拟方法来表征单个硅藻细胞的悬浮特性。结果可能会改变我们对硅藻生态学的看法，它们的营养获取策略，以及控制它们浮力的机制，特别是中央液泡体积和膜的调节。该项目有助于开发单细胞生理研究的新工具，最引人注目的是在不同流动条件下细胞周围扩散边界层的直接测量和细胞水平过程的数值模拟。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This is a project that is jointly funded by the National Science Foundation's Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (UKRI/NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own investigators and component of the work.This project takes a small-scale approach to look at individual cells to investigate the sinking of marine diatoms, which on larger scales has implications for how food for larger organisms, carbon, and organic particles move throughout the ocean. Diatoms are a type of phytoplankton, cells that use photosynthesis in surface waters to produce roughly half of the world’s oxygen and the food to support ocean food webs. They have a heavy, glass-like outer wall which causes them to sink and move up to 40% of particulate organic carbon from the ocean’s surface to the deep sea. The investigators are using novel methods to determine how diatoms regulate their sinking quickly in response to different environmental conditions. These include state-of-the-art video measurements of individual cells, a micoelectrode approach to understand changes at cell surfaces, and microscopy to see changes inside and at the surface of cells. The resulting information will be used to build a model to understand how and why diatoms use unsteady sinking behavior based on their environment. The project supports early career investigators, provides training for a postdoctoral scientist and undergraduate students, and develops a collaboration between US and UK scientists. The team is also developing lesson plans in conjunction with local high schools with high populations of underrepresented students in STEM fields. The problem of sinking and suspension of diatoms has received considerable attention because of its ecological, evolutionary and biogeochemical significance, yet understanding of the processes that regulate sinking rates remains rudimentary. The investigators have used new techniques to make preliminary observations showing that some species of diatom exhibit an unsteady sinking behavior that consists of rapid changes of buoyancy on time scales of seconds. However, it remains unclear how widely this behavior matters across species and ocean conditions. In this study, the team of investigators is using state-of-the-art video-based measurements of sinking rates of individual cells to assess the prevalence of unsteady sinking among centric and pennate diatoms of varying cell sizes and quantify how this behavior changes in response to sharp gradients in nutrients and light. The project leverages an interdisciplinary, international collaboration to combine innovative optical techniques, advanced tools to assess cell physiology, and numerical modeling approaches to characterize suspension properties for individual diatom cells. Results are likely to transform the way we think about the ecology of diatoms, their strategies for nutrient acquisition, and mechanisms to control their buoyancy, in particular the modulation of volume and membrane of the central vacuole. This project contributes to the development of novel tools for single cell physiological studies, most notably direct measurement of diffusive boundary layers around cells under varying flow conditions and numerical modeling of cell-level processes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.