Temperature and Carbon Assimilation Regulate the Chlorosome Biogenesis in Green Sulfur Bacteria

TL;DR

This study investigates how temperature and carbon assimilation influence the structure, composition, and spectral properties of chlorosomes in green sulfur bacteria, revealing a metabolic regulation mechanism for chlorosome biogenesis.

Contribution

It demonstrates the regulation of chlorosome biogenesis by environmental factors and provides a theoretical analysis linking structural changes to spectral modifications.

Findings

Smaller chlorosomes under stress conditions

Simplified BChl c homologues with smaller side chains

Spectral shifts associated with structural changes

Abstract

Green photosynthetic bacteria adjust the structure and functionality of the chlorosome - the light absorbing antenna complex - in response to environmental stress factors. The chlorosome is a natural self-assembled aggregate of bacteriochlorophyll (BChl) molecules. In this study we report the regulation of the biogenesis of the Chlorobaculum tepidum chlorosome by carbon assimilation in conjunction with temperature changes. Our studies indicate that the carbon source and thermal stress culture of Cba. tepidum grows slower and incorporates less BChl c in the chlorosome. Compared with the chlorosome from other cultural conditions we investigated, the chlorosome from the carbon source and thermal stress culture displays: (a) smaller cross-sectional radius and overall size; (b) simplified BChl c homologues with smaller side chains; (c) blue-shifted Qy absorption maxima and (d) a sigmoid-shaped circular dichroism (CD) spectra. Using a theoretical model we analyze how the observed spectral modifications can be associated with structural changes of BChl aggregates inside the chlorosome. Our report suggests a mechanism of metabolic regulation for chlorosome biogenesis.