Low-Temperature Fluorescence from Single Chlorosomes, Photosynthetic Antenna Complexes of Green Filamentous and Sulfur Bacteria
Yutaka Shibata 1*, Yoshitaka Saga 2, Hitoshi Tamiaki 3 and Shigeru Itoh 1
1 Nagoya University
2 Kinki University
3 Ritsumeikan University
* To whom correspondence should be addressed. E-mail: yshibata{at}bio.phys.nagoya-u.ac.jp.
Submitted on March 27, 2006
Revised on May 13, 2006
Accepted on 9 August 2006
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Abstract |
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Fluorescence spectra of single chlorosomes isolated from a green filamentous bacterium [Chloroflexus (Cfl.) aurantiacus] and a green sulfur bacterium [Chlorobium (Cb.) tepidum] were measured by using a confocal laser microscope at 13 K. Chlorosomes were frozen either in a liquid solution (floating chlorosome) or on a quartz plate after being adsorbed (adsorbed chlorosome). Fluorescence peak wavelengths were shorter for the adsorbed single chlorosomes than for the floating ones. Single floating Cfl. chlorosomes showed a distribution of fluorescence peak positions having a center at 759.0 nm with a full width at half maximum (FWHM) of 6.3 nm. Single floating Cb. chlorosomes showed a 782.7 nm center with a FWHM of 3.4 nm. The distribution shifted to the blue and became wider with increasing temperatures, especially in Cb. chlorosomes, suggesting a large excitonic density of states just above the lowest level. Energy transfer (ET) from BChl-c aggregates to BChl-a molecules in the baseplate proteins was observed in the floating chlorosomes but not in the adsorbed ones. A positive correlation was found between the peak wavelength of BChl-c fluorescence and the intensity of BChl-a fluorescence in single Cfl. chlorosomes. The results suggest that the BChl-c aggregates with longer wavelengths of the fluorescence peaks have a more efficient Förster-type ET to the baseplate BChl-a.
Key Words:
Chlorobium tepidum, Chloroflexus aurantiacus, confocal microscope, energy transfer, spectral heterogeneity
