High-frequency S-layer protein variation in Campylobacter fetus revealed by sapA mutagenesis |
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Authors: | Martin J Blaser Enze Wang Murali K R Tummuru Ronald Washburn Shuji Fujimoto Agnès Labigne |
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Institution: | Division of Infectious Diseases, Department of Medicine and Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.;Medical Service, Department of Veterans Affairs Medical Center, Nashville, Tennessee 37212, USA.;Division of infectious Diseases, Bowman Gray School of Medicine, Winston-Salem, North Carolina 27157, USA.;Department of Bacteriology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.;Unitédes Entérobactéries, INSERM U-199, Institut Pasteur, Paris, France. |
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Abstract: | Campylobacter fetus utilizes paracrystalline surface (S-) layer proteins that confer complement resistance and that undergo antigenic variation to facilitate persistent mucosal colonization in ungulates. C. fetus possesses multiple homologues of sapA, each of which encode full-length S-layer proteins. Disruption of sapA by a gene targeting method (insertion of kanamycin (km) resistance) caused the loss of C. fetus cells bearing full-length S-layer proteins and their replacement by cells bearing a 50 kDa truncated protein that was not exported to the cell surface. After incubation of the mutants with serum, the survival rate was approximately 2 × 10-2. Immunoblots of survivors showed that phenotypic reversion involving high-level production of full-length (98, 127 or 149 kDa) S-layer proteins had occurred. Revertants were serum resistant but caused approximately 10-fold less bacteraemia in orally challenged mice than did the wild-type strain. Southern hybridizations of the revertants showed rearrangement of sapA homologues and retention of the km marker. These results indicate that there exists high-frequency generation of C. fetus sapA antigenic variants, and that intracellular mechanisms acting at the level of DNA reciprocal recombination play key roles in this phenomenon. |
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