Determination of the number of bacteriochlorophyll molecules per chlorosome light-harvesting complex in Chlorobium tepidum

Abstract

Chlorosome light-harvesting complexes from Chloroflexus aurantiacus have been examined to determine the bacteriochlorophyll content. Chlorosome isolates from Chloroflexus aurantiacus were used to determine the number of bacteriochlorophyll c molecules (Bchl c) present in each chlorosome. Single molecule fluorescence spectroscopy was used to determine the molar concentration of chlorosomes. In a sample with OD742 ~3, chlorosome concentration was determined to be 1.1x10 -8M and the chlorosomes were found to have a hydrodynamic radius of 22 nm. Pigment extraction and quantitation was used to determine the molar concentration of Bchl c present and a number of 4,500 ± 500 Bchl c per chlorosome was determined. Similar studies using chlorosomes from Chlorobium tepidum are currently in progress. Previously described chlorosome models are being used to determine possible structures using the number of bacteriochorophyll molecules per chlorosome. The results presented have significant implications on chlorosome structure.