Genetic Transfer of Salmonella typhimurium and Escherichia coli Lipopolysaccharide Antigens to Escherichia coli K-12

Abstract

Escherichia coli K-12 ϰ971 was crossed with a smooth Salmonella typhimurium donor, HfrK6, which transfers early the ilv -linked rfa region determining lipopolysaccharide (LPS) core structure. Two ilv + hybrids differing in their response to the LPS-specific phages FO and C21 were then crossed with S. typhimurium HfrK9, which transfers early the rfb gene cluster determining O repeat unit structure. Most recombinants selected for his + (near rfb ) were agglutinated by Salmonella factor 4 antiserum. Transfer of an F′ factor (FS400) carrying the rfb–his region of S. typhimurium to the same two ilv + hybrids gave similar results. LPS extracted from two ilv + , his + , factor 4-positive hybrids contained abequose, the immunodominant sugar for factor 4 specificity. By contrast, his + hybrids obtained from ϰ971 itself by similar HfrK9 and F′FS400 crosses were not agglutinated by factor 4 antiserum, indicating that the parental E. coli ϰ971 does not have the capacity to attach Salmonella O repeat units to its LPS core. It is concluded that the Salmonella rfb genes are expressed only in E. coli ϰ971 hybrids which have also acquired ilv -linked genes (presumably rfa genes affecting core structure or O-translocase ability, or both) from a S. typhimurium donor. When E. coli ϰ971 was crossed with a smooth E. coli donor, Hfr59, of serotype O8, which transfers his early, most his + recombinants were agglutinated by E. coli O8 antiserum and lysed by the O8-specific phage, Ω8. This suggests that, although the parental E. coli K-12 strain ϰ971 cannot attach Salmonella -specific repeat units to its LPS core, it does have the capacity to attach E. coli O8-specific repeat units.