Abstract
Photosynthesis transfers energy efficiently through a series of antenna complexes to the reaction center where charge separation occurs. Energy transfer in vivo is primarily monitored by measuring fluorescence signals from the small fraction of excitations that fail to result in charge separation. Here, we use two-dimensional electronic spectroscopy to follow the entire energy transfer process in a thriving culture of the purple bacteria, Rhodobacter sphaeroides. By removing contributions from scattered light, we extract the dynamics of energy transfer through the dense network of antenna complexes and into the reaction center. Simulations demonstrate that these dynamics constrain the membrane organization into small pools of core antenna complexes that rapidly trap energy absorbed by surrounding peripheral antenna complexes. The rapid trapping and limited back transfer of these excitations lead to transfer efficiencies of 83% and a small functional light-harvesting unit.
Highlights
Photosynthesis transfers energy efficiently through a series of antenna complexes to the reaction center where charge separation occurs
We overcome the longstanding obstacle of intensely scattered light[15, 16] and recover the native dynamics of energy transfer through the dense network of antenna complexes and into the RC. 2DES spectra correlate excitation energy along the ωτ-axis with stimulated emission (SE), ground state bleach (GSB), and excited state absorption (ESA) energies along the ωt-axis as a function of an ultrafast time delay, T, known as the waiting time (Supplementary Fig. 1)[17, 18]
Measuring energy transfer dynamics in well-connected systems of identical subunits, like those found in photosynthetic membranes, presents two key experimental challenges
Summary
Photosynthesis transfers energy efficiently through a series of antenna complexes to the reaction center where charge separation occurs. By removing contributions from scattered light, we extract the dynamics of energy transfer through the dense network of antenna complexes and into the reaction center. Photosynthesis relies on ultrafast energy transfer to efficiently move energy from the site of absorption (photosynthetic antenna) to the site of charge separation (photosynthetic reaction center, RC) on a picosecond timescale[1, 2]. These processes are crucial for the organism’s fitness and are tightly regulated and optimized for safe harvesting of solar energy[3,4,5,6]. The energy transfer dynamics observed in vivo in conjunction with simulations constrain the membrane organization into small
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