A Salmonella typhimurium virulence gene linked to flg

Abstract

Isogenic pairs of strains of Salmonella typhimurium which differed only in whether or not they were flagellate were found to be equally virulent in C57BL/6J mice infected orally, intravenously, or intraperitoneally. Therefore, we investigated the genetic basis of our previous observation that in this mouse model, nonflagellate ΔflgABCDE25 strains were reduced in virulence compared with isogenic wild-type flagellate strains. The recombinant plasmid pMH6, which contains several flg+ genes and a segment of the S. typhimurium chromosome adjacent to the flg genes, was introduced into a ΔflgABCDE25 mutant. This restored virulence in mice challenged intraperitoneally, which suggested that a virulence gene occurs adjacent to the flg genes. When plasmid pMH64, which lacks the chromosomal segment adjacent to the flg genes, was introduced into the same ΔflgABCDE25 mutant, virulence was not restored. In contrast, the introduction of pMH71, a plasmid which retains the chromosomal segment adjacent to the flg genes, restored virulence. We conclude that a hitherto unknown virulence gene, which we have named mviS, occurs adjacent to the flg genes and that its absence in ΔflgABCDE25 mutants, rather than the nonflagellate phenotype of the ΔflgABCDE25 mutants, caused the previously reported attenuation of such mutants.