The Vi antigen and somatic antigen 9 were transferred to Salmonella typhimurium recipients by mating with S. typhosa Hfr TD-7, and the genetic determinants of these antigens were located. A gene responsible for Vi antigen expression, ViB, was found to be associated with the inl-purA-pyrB linkage group, and the order ViB-inl-purA-pyrB was established. The determinant of somatic antigen 9 was found closely linked to the his gene, and cotransduction of these determinants was accomplished with phage PLT-22. Moreover, all conjugation and transduction hybrids which received the somatic antigen 9 determinant concurrently lost somatic antigen 4. Similarly, S. typhosa hybrids produced by transfer of his and the gene for somatic antigen 4 from S. typhimurium Hfr B2, or by cotransduction tion of these genes with PLT-22, also lost somatic antigen 9. These results indicated that the genetic determinants of the somatic antigens 9 and 4 are probably allelic. A second Vi antigen determinant, ViA, located near his, was discovered in matings of S. typhimurium Hfr B2 with a Vi-negative S. typhosa recipient. Vi-positive S. typhosa hybrids were obtained from this cross in which neither parent expressed the Vi antigen, indicating that this Vi determinant of S. typhosa is present also in S. typhimurium. The intricate serological pattern exhibited by members of the family Enterobacteriaceae has come, in recent years, within the scope of genetic
The relative chromosomal location of the ViA determinant, a gene required for Vi antigen expression in Salmonella typhosa (and present also in S. typhimurium), was examined in S. typhimurium X S. typhosa matings. The position of this gene was determined with respect to the histidine (his) and methionine (metG) biosynthesis markers, and to the genetic determinants of somatic antigens 5 (0-5) and 4 (0-4) of S. typhimurium. The gene order established by analyses of the hybrid classes resulting from the genetic crosses was ViA-0-5-metG-0-4 (his). This order suggests that neither ViA nor 0-5 is a member of the complex of functionally related structural genes which constitute the 0-4 locus. It allows for the possibility, however, of a functional relationship between the genes of the ViA and 0-5 loci. At least two genetic determinants have been shown to be responsible for the expression of the Vi antigen of Salmonella typhosa (7). One of these, designated ViB, maps adjacent to the inositol utilization (inl) locus on the Salmonella chromosome. Introduction of the ViB gene into S. typhimurium by conjugation with an S. typhosa Hfr strain results in the expression of the Vi antigen in S. typhimurium. Thus, the absence of the ViB gene (or gene complex), or its failure to function, appears to be responsible for the lack of expression of the Vi antigen in S. typhimurium
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