Bacterial Photosynthetic Design and Adaptation Probed by Multidimensional Spectroscopies

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

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.