Bacterial Photosynthetic Design and Adaptation Probed by Multidimensional Spectroscopies

在光合作用中，光合能量转移和电荷分离的主要过程以接近单位量子效率发生。这种惊人效率的基础是能量景观，它提供了从天线到反应中心的超快速定向能量转移，以及反应中心内的定向电子转移。暴露在强光和活性氧下，植物和细菌系统采用复杂的适应性来重塑它们的能量景观，以最大限度地减少光损伤。非线性光谱学在发展我们目前对光合作用设计原理的理解方面发挥了重要作用。二维电子能谱（2DES）已被证明是揭示植物电子结构和光合能量传递途径的有力工具。它还揭示了量子相干动力学，其物理起源一直备受争议。在许多光合系统中，这些相干动力学被认为是由电子振动共振引起的，这可能对光合能量转移和电荷分离很重要。本项目旨在提高当前多维光谱的空间分辨率和获取暗态的能力，将2DES与荧光检测的2DES （F- 2DES）相结合，研究紫色细菌体内的能量格局、量子相干动力学和适应机制。充分理解光合作用设计原理需要超越以往的研究，这些研究主要集中在单个光合复合体的纯化溶液上，以研究这些成分如何在它们的光谱特性、相对组成和空间组织被重塑以适应不断变化的环境条件时协同工作。该项目还将为参与该项目的研究生和本科生提供广泛的科学培训。该项目将加强现有的光谱工具，用于探测当地生物环境的动态和研究自然和人工系统中的能量转移。紫色细菌光合网络的广泛实验表征将推动多色系统电子结构和动力学理论模型的发展。我们从使用紫色细菌作为模型系统中获得的理解可以指导未来人工光收集材料的设计。在PI于2008年和2015年成功举办物理学本科女生会议（CUWiP）的基础上，该项目将于2021年在密歇根大学举办一次CUWiP会议。这次会议将邀请约150名来自中西部地区的女性来了解物理学的职业机会和研究，并加强美国物理学女性的网络。该项目还将通过指导科学奥林匹克竞赛团队和参观底特律地区经济困难学生的实验室，支持向当地小学推广。该研究项目将扩展多维光谱的工具集，以提供前所未有的灵敏度、空间分辨率和进入暗态，从而实现光合作用功能的体内研究。本研究将以紫色细菌为模型系统，研究紫色细菌量子相干性的物理性质、功能相关性和真失相时间，紫色细菌如何重塑其能量景观以适应高光和弱光条件，以及紫色细菌如何在有氧环境中适应其光保护机制。通过揭示简单细菌系统中的光合作用设计原理，该项目旨在为更好地理解植物光系统铺平道路。这种理解是一种基本的追求，它将使我们能够向大自然学习，通过开发人工光收集系统和生物燃料来满足我们自己的能源需求。该项目由物理系的生命系统物理学项目和分子与细胞生物科学系的分子生物物理学项目共同支持。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。

In photosynthesis, the primary processes of photosynthetic energy transfer and charge separation occur with near unit quantum efficiency. Underlying this stunning efficiency is the energy landscape that provides ultrafast directional transfer of energy from antennae to reaction centers, and directional electron transfer within reaction centers. Exposed to high light and reactive oxygen species, plant and bacterial systems employ intricate adaptations that remodel their energy landscape to minimize photodamage. Nonlinear spectroscopy has played an important role in developing our current understanding of photosynthetic design principles. Two-dimensional electronic spectroscopy (2DES) has proven to be a powerful tool for revealing electronic structure and photosynthetic energy transfer pathways. It has also revealed quantum coherent dynamics, the physical origin of which has been hotly debated. In a number of photosynthetic systems, these coherent dynamics have been proposed to arise from electronic-vibrational resonances that may be important for photosynthetic energy transfer and charge separation. This project aims to improve the spatial resolution and ability to access dark states of current multidimensional spectroscopies and employ a combination of 2DES and fluorescence-detected 2DES (F- 2DES) to study the energy landscape, quantum coherent dynamics, and adaptive mechanisms in purple bacteria in vivo. Full understanding of photosynthetic design principles requires moving beyond previous studies that have primarily focused on purified solutions of individual photosynthetic complexes to examine how these components work together as their spectroscopic properties, relative composition and spatial organization is remodeled to adapt to changing environmental conditions. The project will also provide extensive scientific training for the graduate and undergraduate students working on the project. The project will enhance the available spectroscopic tools for probing the dynamics of local biological environments and studying energy transfer in natural and artificial systems. The extensive experimental characterization of the purple bacterial photosynthetic network will drive the development of theoretical models of the electronic structure and dynamics of multichromophoric systems. The understanding we gain from using purple bacteria as a model system may guide the future design of artificial light-harvesting materials. Building on the PI's previous success in hosting the Conference for Undergraduate Women in Physics (CUWiP) in 2008 and 2015, the project will aim to host a CUWiP meeting at the University of Michigan in 2021. The meeting will seek to bring ~150 women from across the Midwest to learn about career opportunities and research in Physics and strengthen the network of US women in Physics. The project will also support outreach to local elementary schools through coaching of Science Olympiad teams and lab tours to economically disadvantaged students from the Detroit region.This research project will expand the toolset of multidimensional spectroscopies to provide unprecedented sensitivity, spatial resolution and access to dark states to enable in vivo studies of photosynthetic function. Using purple bacteria as a model system this research will address the physical nature, functional relevance, and true dephasing time of quantum coherence in purple bacteria, how do purple bacteria remodel their energy-landscape to adapt to high and low light conditions, and how do purple bacteria adapt their photoprotection mechanisms in aerobic environments. By uncovering photosynthetic design principles in the simpler bacterial systems the PI aims to pave the way for a better understanding of plant photosystems. Such an understanding is a fundamental pursuit that will enable us to learn from Nature to meet our own energy needs through the development of artificial light-harvesting systems and biofuels.This project is being jointly supported by the Physics of Living Systems program in the Division of Physics and the Molecular Biophysics program in the Division of Molecular and Cellular Biosciences.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.