INSERTIONAL INACTIVATION STUDIES OF THE CSMA AND CSMC GENES OF THE GREEN SULFUR BACTERIUM CHLOROBIUM-VIBRIOFORME-8327 - THE CHLOROSOME PROTEIN CSMA IS REQUIRED FOR VIABILITY BUT CSMC IS DISPENSABLE

Targeted mutagenesis was used to investigate the roles of the CsmA and CsmC proteins of the chlorosomes of the green bacteria Chlorobium tep idum and Chlorobium vibrioforme 8327. Under the photoautotrophic growt h conditions employed, CsmA is required for the viability of the cells but CsmC is dispensable. The absence of CsmC caused a small red shift in the near-infrared absorption maximum of bacteriochlorophyll d in w hole cells and chlorosomes, bur chlorosomes were assembled in and coul d be isolated from the csmC mutant. The doubling time of the csmC muta nt was approximately twice that of the wild-type strain. Fluorescence emission measurements suggested that energy transfer from the bulk bac teriochlorophyll d to another pigment, perhaps bacteriochlorophyll a, emitting at 800-804 nm, was less efficient in the csmC mutant cells th an in wild-type cells. These studies establish that transformation and homologous recombination can be employed in targeted mutagenesis of C hlorobium sp. and further demonstrate that chlorosome proteins play im portant roles in the structure and function of these light-harvesting organelles. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.