Campylobacter fetus sapInversion Occurs in the Absence of RecA Function

ABSTRACTPhase variation of Campylobacter fetussurface layer proteins (SLPs) occurs by inversion of a 6.2-kb DNA segment containing the unique sappromoter, permitting expression of a single SLP-encoding gene. Previous work has shown that theC. fetus sapinversion system is RecA dependent. When we challenged a pregnant ewe with a recAmutant of wild-typeC. fetus(strain 97-211) that expressed the 97-kDa SLP, 15 of the 16 ovine-passaged isolates expressed the 97-kDa protein. However, one strain (97-209) expressed a 127-kDa SLP, suggesting that chromosomal rearrangement may have occurred to enable SLP switching. Lack of RecA function in strains 97-211 and 97-209 was confirmed by their sensitivity to the DNA-damaging agent methyl methanesulfonate. Southern hybridization and PCR of these strains indicated that the aphAinsertion into recAwas stably present. However, Southern hybridizations demonstrated that in strain 97-209 inversion had occurred in the saplocus. PCR data confirmed inversion of the 6.2-kb DNA element and indicated that in these recAmutants the sapinversion frequency is reduced by 2 to 3 log10units compared to that in the wild type. Thus, although the major sapinversion pathway in C. fetusis RecA dependent, alternative lower-frequency, RecA-independent inversion mechanisms exist.