title: High-frequency S-layer protein variation in Campylobacter fetus revealed by sapA mutagenesis.
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 x 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.
authors.affiliation: Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
authors.forename: M J
authors.initials: MJ
authors.lastname: Blaser
authors.forename: E
authors.initials: E
authors.lastname: Wang
authors.forename: M K
authors.initials: MK
authors.lastname: Tummuru
authors.forename: R
authors.initials: R
authors.lastname: Washburn
authors.forename: S
authors.initials: S
authors.lastname: Fujimoto
authors.forename: A
authors.initials: A
authors.lastname: Labigne
mesh_terms: D000818:Animals; D000940:Antigenic Variation; D000942:Antigens, Bacterial / Q000235:genetics; D016470:Bacteremia / Q000209:etiology; D001426:Bacterial Proteins / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification; D001770:Blood Bactericidal Activity; D002168:Campylobacter fetus / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity; D002874:Chromosome Mapping; D003165:Complement System Proteins / Q000378:metabolism; D003227:Conjugation, Genetic; D004926:Escherichia coli / Q000235:genetics; D005613:Freeze Etching; D015870:Gene Expression; D005798:Genes, Bacterial; D005822:Genetic Vectors; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins; D051379:Mice; D016296:Mutagenesis
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D008562:Membrane Glycoproteins; C055764:S-layer proteins; D003165:Complement System Proteins