Morphology and spectroscopy of chlorosomes from Chlorobium tepidum by alcohol treatments

Chlorosomes from Chlorobium tepidum have been treated with alcohol-saturated buffers, followed by dilution to the buffers with half the saturated concentrations. Morphologic changes during this process have been statistically investigated by dynamic light scattering technique combined with electron microscopy to obtain the complete information on shape, size and distribution, while spectral properties have been studied by absorption, CD and magnetic circular dichroism. Three alcohols (1-hexanol, 1-butanol and phenol) have been found to produce nearly reversible conversion of absorption spectra despite the more than 15-times difference in the alcohol concentration. It is shown that the degree of saturation, not the alcohol concentration, is the key factor for the complete conversion of bacteriochlorophyll c in chlorosomes from the aggregated state to the monomeric form. We have observed substantial changes in the shape, size and distribution at each step of the treatment with 1-hexanol, indicating that the whole process is morphologically irreversible. Comparison of the morphologic changes with the corresponding spectroscopic behaviour suggests that the relative overall size rather than the shape and distribution may be a more important factor affecting the spectral properties.