Genetic Transfer of Salmonella O Antigens to Escherichia coli 08

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Abstract
Summary His+ hybrids from a cross between a Salmonella typhimurium donor and an Escherichia coli 08 recipient expressed E. coli 08 specificity and in addition Salmonella 04,12-specificity. This indicated that the recipients had received the his-linked donor rfb cluster determining the synthesis of S. typhimurium O-specific repeat units and that the rfb genes of both mating partners are functional in these hybrids. Chemical analyses showed that the hybrids contained an E. coli 08 lipopolysaccharide (0 antigen) and a S. typhimurium specific lipopolysaccharide with only one O-specific repeat unit (SR antigen). 08-negative mutants selected from the 08-positive hybrids retained the Salmonella O-specificity and represent semi-rough (SR) forms, because the rfc gene(s) determining the polymerization of repeat units has not been transferred. Attempts to introduce the S. typhimurium rfc locus into E. coli 08 remained unsuccessful. Crosses between a S. typhi donor and E. coli 08 gave rise to smooth (S) and SR His+ recombinants exhibiting only S. typhi O-specificity. The smooth recombinants are assumed to have obtained the his-linked rfb cluster and in addition the rfc gene(s) of the donor. The exchange of the rfb region of such smooth recombinants by that of a S. typhimurium donor led to smooth hybrids with 04,(5), 12-specificity. The phenotypically smooth recombinants exhibited concomitantly S-and SR-lipopolysaccharides of S. typhi and S. typhimurium O-specificity, respectively.