NEAR-INFRARED-FT-RAMAN STUDY OF AGGREGATION OF BACTERIOCHLOROPHYLL c IN WHOLE LIVING Chlorobium limicola

Near-infrared excited Fourier-transform Raman spectra have been measured for whole living Chlorobium limicola f. thiosulfatophilum to explore in situ structure of bacteriochlorophyll c (BChl-c). The spectra, whose Raman bands are preresonance enhanced via a Qy band of BChl-c, did not contain contributions from the major components of bacteria such as proteins and lipids. Therefore, the spectra provide selective structural information about BChl-c in the chlorosomes in a totally nondestructive manner. A marker band, appearing at 1605 cm-1 for the coordination number of the Mg atom, shows that BChl-c in the chlorosomes is five coordinate. The Raman spectrum of living bacteria closely resembles that of BChl-c in water-saturated carbon tetrachloride (w-std CC14) where it is comprised of dimer, tetramer and polymer spectra. However, a band assigned to a C=O stretching mode of the 131-keto group is identified only at 1641 cm-1. A band arising from the free keto carbonyl group, which appears in the spectrum of BChl-c in w-std CC14, is not observed in the spectra of bacteria. These observations suggest that BChl-c in the chlorosomes forms mostly coordinate polymeric species whose structure is very similar to that of BChl-c in w-std CC14.