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J. Bacteriol. doi:10.1128/JB.01711-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

INITIAL CHARACTERIZATION OF THE PHOTOSYNTHETIC APPARATUS OF ‘CHLOROTHRIX HALOPHILA’: A FILAMENTOUS, ANAEROBIC PHOTOAUTOTROPH

Department of Chemistry and Biochemistry, P.O. Box 871604, Arizona State University, Tempe, AZ 85287-1604; Departments of Biology and Chemistry, Washington University, St. Louis, MO, 63130

^* To whom correspondence should be addressed. Email: Blankenship{at}wustl.edu.

	Abstract

‘Chlorothrix (Cx.) halophila’ is a recently described halophilic, filamentous anoxygenic photoautotroph (19) enriched from the hypersaline microbial mats at Guerrero Negro, Mexico. Analysis of the photosynthetic apparatus by negative staining, spectroscopy, and SDS-PAGE indicates that the photosynthetic apparatus in this organism has similarities to both the Chloroflexi and Chlorobi phyla of green photosynthetic bacteria. The chlorosomes were found to be ellipsoidal in shape and variable in size, which is comparable to chlorosomes from other species of green photosynthetic bacteria. The absorption spectrum of the whole cell is dominated by the chlorosome bacteriochlorophyll c (BChl c) peak at 759 nm, with fluorescence emission at 760 nm. A second fluorescence emission band is observed at 870 nm and is tentatively attributed to a membrane-bound antenna complex. Fluorescence emission spectra taken at 77 K indicate another complex that fluoresces at 820 nm, which probably arises from the chlorosome baseplate complex. All of these results suggest the presence of BChl c in the chlorosomes, the presence of bacteriochlorophyll a (BChl a) in the baseplate and a membrane-bound antenna complex. Analysis of the proteins in the chlorosomes revealed the presence of a 6 kDa band, which was found to be related to the BChl c binding protein CsmA found in other green bacteria. Overall, the absorbance and fluorescence spectra of ‘Cx. halophila’ reveal an interesting mix of photosynthetic characteristics that seem to have properties similar to both phyla of green bacteria when compared to Chlorobium tepidum and Chloroflexus aurantiacus.