Interplay between excitation kinetics and reaction-center dynamics in purple bacteria

TL;DR

This paper investigates how excitation transfer and reaction-center dynamics interact in purple bacteria, revealing a transition in membrane architecture driven by illumination levels that optimize energy use and dissipation.

Contribution

It introduces a stochastic hopping rate model to explain the illumination-driven transition in membrane architecture of purple bacteria, linking excitation kinetics to reaction-center behavior.

Findings

Transition in membrane architecture with illumination

Efficient energy metabolism at low light

Dissipation prevents energy oversupply at high light

Abstract

Photosynthesis is arguably the fundamental process of Life, since it enables energy from the Sun to enter the food-chain on Earth. It is a remarkable non-equilibrium process in which photons are converted to many-body excitations which traverse a complex biomolecular membrane, getting captured and fueling chemical reactions within a reaction-center in order to produce nutrients. The precise nature of these dynamical processes -- which lie at the interface between quantum and classical behaviour, and involve both noise and coordination -- are still being explored. Here we focus on a striking recent empirical finding concerning an illumination-driven transition in the biomolecular membrane architecture of {\it Rsp. Photometricum} purple bacteria. Using stochastic realisations to describe a hopping rate model for excitation transfer, we show numerically and analytically that this surprising shift in preferred architectures can be traced to the interplay between the excitation kinetics and the reaction center dynamics. The net effect is that the bacteria profit from efficient metabolism at low illumination intensities while using dissipation to avoid an oversupply of energy at high illumination intensities.