Mapping The Ultrafast Flow Of Harvested Solar Energy In Living Photosynthetic Cells

TL;DR

This study employs two-dimensional electronic spectroscopy to elucidate the ultrafast energy transfer dynamics in living photosynthetic bacteria, revealing highly efficient, small-scale light-harvesting units with rapid energy trapping.

Contribution

It introduces a novel spectroscopic approach to directly observe energy transfer in vivo, uncovering the organization and efficiency of photosynthetic antenna complexes.

Findings

Energy transfer dynamics constrain membrane organization to small pools of core complexes.

Transfer efficiency is approximately 83%.

Rapid trapping limits back transfer, optimizing energy flow.

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 to be 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.