Assembly of extramembranous light-harvesting complexes of green sulfur photosynthetic bacterium Chlorobium tepidum on glass surface by electrostatic layer-by-layer adsorption

Extramembranous and peripheral light-harvesting complexes (chlorosomes) of green sulfur photosynthetic bacterium Chlorobium tepidum were electrostatically immobilized on a pyrex glass plate with the help of cationic polylysines. Absorbance of both Soret and Qy bands of chlorosomes were linearly increased by repeated manipulation of layer-by-layer adsorption. Spectral features of chlorosome/polylysine layers on the glass plate indicate that the supramolecular structures of self-aggregates of bacteriochlorophyll(BChl)-c in chlorosomes are maintained on the solid surface. BChl-c molecules could be completely extracted from a single chlorosome/polylysine layer on a glass plate as monomers in acetone. Visible absorption spectra of extracted pigments indicate that BChl-c molecules inside chlorosomes were not denatured by electrostatic adsorption of chlorosomes and that the amount of BChl-c molecules in chlorosomes adsorbed on a glass plate was (1.3 ± 0.05) × 10− 10 mol/cm2 (mean ± standard deviation, three measurements). The estimation of BChl-c amounts suggests that chlorosomes are not so densely immobilized on a polylysine-adsorbed quartz plate.