HIGH-FREQUENCY S-LAYER PROTEIN VARIATION IN CAMPYLOBACTER-FETUS REVEALED BY SAPA MUTAGENESIS

Campylobacter fetes utilizes paracrystalline surface (S-) layer protei ns that confer complement resistance and that undergo antigenic variat ion to facilitate persistent mucosal colonization in ungulates. C. fet us possesses multiple homologues of sapA, each of which encode full-le ngth S-layer proteins. Disruption of sapA by a gene targeting method ( insertion of kanamycin (km) resistance) caused the loss of C. fetus ce lls bearing full-length S-layer proteins and their replacement by cell s bearing a 50 kDa truncated protein that was not exported to the cell surface. After incubation of the mutants with serum, the survival rat e was approximately 2 x 10(-2). Immunoblots of survivors showed that p henotypic 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 hybridization s of the revertants showed rearrangement of sapA homologues and retent ion of the km marker. These results indicate that there exists high-fr equency generation of C. fetus sapA antigenic variants, and that intra cellular mechanisms acting at the level of DNA reciprocal recombinatio n pray key roles in this phenomenon.