Participation of Lipopolysaccharide Genes in the Determination of the Enterobacterial Common Antigen: Analysis in Salmonella Groups B and C1

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RESUMO

The enterobacterial common antigen (CA) is present in salmonellae of groups B (S. typhimurium) and C1 (S. montevideo). Mutation at the rfe gene(s), which is required for the biosynthesis of O side chains of the lipopolysaccharide in group C1 (S-6, 7) but not in group B (S-4, 12), destroys the capacity of the bacteria to synthesize CA. When such mutated group C1rfe genes (C-rfe−) were introduced into group B strains, the hybrids also became CA− and could be restored to CA+ by introduction of either C-rfe+ or B-rfe+ (corresponding genetic region in group B). This indicated the presence of genes for CA synthesis at the rfe site in both groups B and C1. In rfe− mutants of group C1, which were rough and CA−, the CA+ phenotype could be restored by replacing the rfe− gene(s) with C-rfe+. In contrast, B-rfe+ was able to support the synthesis of trace amounts of CA only, although it was sufficient to restore their ability to synthesize the S-6, 7 side chain of the lipopolysaccharide. Corresponding hybrids (B-rfe+, C-rfb+ or C-rfb−) were constructed by introducing the C-rfb genes into a group B strain; they also showed only a trace of CA reactivity.

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