Glucosylation of lipopolysaccharide in Salmonella: mutants negative for O antigen factor 1221

In salmonella O group B, the O antigen factor 12(2) is created by glucosylation at C4 of the galactose units of the O side chains; phage-determined glucosylation at C6 of these galactose units yields factor 1. 12(2)-negative mutants were isolated from 12(2) (+) (stable) parents (genetically oafR(+st)). All 20 mutants studied were stable in respect of their 12(2) character. In eight of them, lysogenization by phage P22 resulted in the appearance of the 12(2) factor-these were interpreted to be defective in the enzyme(s) needed to synthesize the glucose-lipid intermediate that participates in both 12(2)- and 1-specific glucosylation; the corresponding cistron was termed oafE. This "complementation" assay also demonstrated that the P22 genome can determine the synthesis of this glucose-lipid intermediate. The 12(2) character in the oafE(-) mutants became variable after P22 lysogenization, corresponding to factor 1 variation normally determined by this phage. In the remaining 12 mutants, P22 caused the appearance of a variable factor 1, but not of 12(2). The lesion in all the 12(2) mutants was mapped close to the gene purE at min 19 of the Salmonella map. This is the same area where the locus oafR that controls the variation (stable or variable, + or -) of 12(2) had been previously mapped. The results suggest the presence of a 12(2) glucosylation operon in this region.