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

这是一个由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理事会(UKRI/NERC)通过NSF/GEO-NERC牵头机构协议共同资助的项目。该协定允许美国和英国提交一个单一的联合提案，并由该机构进行同行审查，该机构的调查员在预算中所占比例最大。在成功地共同确定奖项后，每个机构将为预算的比例以及与其自己的调查人员和工作部分相关的调查人员提供资金。该项目采用小规模方法来观察单个细胞，以调查海洋硅藻的下沉，这在更大的尺度上对较大生物的食物、碳和有机颗粒如何在海洋中移动具有影响。硅藻是浮游植物的一种，这种细胞利用地表水中的光合作用产生世界上大约一半的氧气和食物来维持海洋食物网。它们有一个沉重的玻璃状外壁，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的方法来确定硅藻如何根据不同的环境条件快速调节它们的下沉。其中包括对单个细胞的最先进的视频测量，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。所得到的信息将被用来建立一个模型，以了解硅藻如何以及为什么根据它们所处的环境使用不稳定的下沉行为。该项目支持早期职业研究人员，为博士后科学家和本科生提供培训，并发展美国和英国科学家之间的合作。该团队还与STEM领域学生人数较少的当地高中一起制定了教学计划。硅藻的下沉和悬浮问题因其生态、进化和生物地球化学意义而受到相当大的关注，但对调节下沉速率的过程的了解仍处于初级阶段。研究人员使用新技术进行了初步观察，发现一些种类的硅藻表现出一种不稳定的下沉行为，包括在几秒钟的时间尺度上浮力的快速变化。然而，目前尚不清楚这种行为对不同物种和海洋条件的影响有多大。在这项研究中，研究团队使用最先进的基于视频的单个细胞下沉率的测量来评估不同细胞大小的中心和羽状硅藻中不稳定下沉的流行率，并量化这种行为如何随着营养和光线的急剧梯度而变化。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，以及数值建模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的看法，它们获取营养的策略，以及控制它们浮力的机制，特别是对中央液泡的体积和膜的调节。该项目对单细胞生理学研究的新工具的开发做出了贡献，最突出的是在变化的流动条件下对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NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为是值得支持的。

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.