T2 lipopolysaccharide antigen of Salmonella: genetic determination of T2 and properties of the T2, T2,S, and T2,SR Forms.

The T2 antigenic form of Salmonella bareilly was examined. The absence of O specificity in this strain was shown to be due to its nonfunctional rfb genes; when the rfb gene cluster was replaced by the rfb cluster derived from smooth donor strains, T2,S and T2,SR recombinants were produced that expressed both T2 and either 0-6,7 or 0-4,12 specificity, depending on O antigen of the donor strain. The T2, T2,S, and T2,SR forms were all unstable on culture and segregated T2-negative forms (R, S, and SR, respectively) at a high rate. In all these respects the T2 antigen closely resembled the other T-form antigen, T1. The genes responsible for the T2 antigen, rfu, were not close to rfb, but their precise location and relation to rft (which determines T1 antigen) could not be discovered because of the instability to the T2 form and low recombination frequency in the necessary interspecies crosses.