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Journal of Bacteriology, November 2009, p. 7109-7120, Vol. 191, No. 22
0021-9193/09/$08.00+0     doi:10.1128/JB.00707-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Envelope Proteins of the CsmB/CsmF and CsmC/CsmD Motif Families Influence the Size, Shape, and Composition of Chlorosomes in Chlorobaculum tepidum{triangledown} ,{dagger}

Hui Li{ddagger} and Donald A. Bryant*

Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802

Received 31 May 2009/ Accepted 8 September 2009

The chlorosome envelope of Chlorobaculum tepidum contains 10 proteins that belong to four structural motif families. A previous mutational study (N.-U. Frigaard, H. Li, K. J. Milks, and D. A. Bryant, J. Bacteriol. 186:646-653, 2004) suggested that some of these proteins might have redundant functions. Six multilocus mutants were constructed to test the effects of eliminating the proteins of the CsmC/CsmD and CsmB/CsmF motif families, and the resulting strains were characterized physiologically and biochemically. Mutants lacking all proteins of either motif family still assembled functional chlorosomes, and as measured by growth rates of the mutant strains, light harvesting was affected only at the lowest light intensities tested (9 and 32 µmol photons m–2 s–1). The size, composition, and biogenesis of the mutant chlorosomes differed from those of wild-type chlorosomes. Mutants lacking proteins of the CsmC/CsmD motif family produced smaller chlorosomes than did the wild type, and the Qy absorbance maximum for the bacteriochlorophyll c aggregates in these chlorosomes was strongly blueshifted. Conversely, the chlorosomes of mutants lacking proteins of the CsmB/CsmF motif family were larger than wild-type chlorosomes, and the Qy absorption for their bacteriochlorophyll c aggregates was redshifted. When CsmH was eliminated in addition to other proteins of either motif family, chlorosomes had smaller diameters. These data show that the chlorosome envelope proteins of the CsmB/CsmF and CsmC/CsmD families play important roles in determining chlorosome size as well as the assembly and supramolecular organization of the bacteriochlorophyll c aggregates within the chlorosome.

* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, S-235 Frear Building, The Pennsylvania State University, University Park, PA 16802. Phone: (814) 865-1992. Fax: (814) 863-7024. E-mail: dab14{at}psu.edu

{triangledown} Published ahead of print on 11 September 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: Department of Laboratory Medicine, University of Washington Medical Center, Seattle, WA 98104.

Journal of Bacteriology, November 2009, p. 7109-7120, Vol. 191, No. 22
0021-9193/09/$08.00+0     doi:10.1128/JB.00707-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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