Nanosecond Laser Photolysis Studies of Chlorosomes and Artificial Aggregates Containing Bacteriochlorophyll e: Evidence for the Proximity of Carotenoids and Bacteriochlorophyll a in Chlorosomes from Chlorobium phaeobacteroides strain CL1401¶

Polymer-Chlorosome Nanocomposites Consisting of Non-Native Combinations of Self-Assembling Bacteriochlorophylls

Chlorosomes are one of the characteristic light-harvesting antennas from green sulfur bacteria. These complexes represent a unique paradigm: self-assembly of bacteriochlorophyll pigments within a lipid monolayer without the influence of protein. Because of their large size and reduced complexity, they have been targeted as models for the development of bioinspired light-harvesting arrays. We report the production of biohybrid light-harvesting nanocomposites mimicking chlorosomes, composed of amphiphilic diblock copolymer membrane bodies that incorporate thousands of natural self-assembling bacteriochlorophyll molecules derived from green sulfur bacteria. The driving force behind the assembly of these polymer-chlorosome nanocomposites is the transfer of the mixed raw materials from the organic to the aqueous phase. We incorporated up to five different self-assembling pigment types into single nanocomposites that mimic chlorosome morphology. We establish that the copolymer-BChl self-assembly process works smoothly even when non-native combinations of BChl homologues are included. Spectroscopic characterization revealed that the different types of self-assembling pigments participate in ultrafast energy transfer, expanding beyond single chromophore constraints of the natural chlorosome system. This study further demonstrates the utility of flexible short-chain, diblock copolymers for building scalable, tunable light-harvesting arrays for technological use and allows for an in vitro analysis of the flexibility of natural self-assembling chromophores in unique and controlled combinations.

Chlorosome antenna complexes from green photosynthetic bacteria

Chlorosomes are the distinguishing light-harvesting antenna complexes that are found in green photosynthetic bacteria. They contain bacteriochlorophyll (BChl) c, d, e in natural organisms, and recently through mutation, BChl f, as their principal light-harvesting pigments. In chlorosomes, these pigments self-assemble into large supramolecular structures that are enclosed inside a lipid monolayer to form an ellipsoid. The pigment assembly is dictated mostly by pigment-pigment interactions as opposed to protein-pigment interactions. On the bottom face of the chlorosome, the CsmA protein aggregates into a paracrystalline baseplate with BChl a, and serves as the interface to the next energy acceptor in the system. The exceptional light-harvesting ability at very low light conditions of chlorosomes has made them an attractive subject of study for both basic and applied science. This review, incorporating recent advancements, considers several important aspects of chlorosomes: pigment biosynthesis, organization of pigments and proteins, spectroscopic properties, and applications to bio-hybrid and bio-inspired devices.