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Glucosylation of Lipopolysaccharide in Salmonella: Mutants Negative for O Antigen Factor 12₂¹

^a Central Public Health Laboratory (State Serum Institute) Helsinki, Finland

ABSTRACT

In salmonella O group B, the O antigen factor 12₂ 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. 12₂-negative mutants were isolated from 12₂⁺ (stable) parents (genetically oafR^+st). All 20 mutants studied were stable in respect of their 12₂ character. In eight of them, lysogenization by phage P22 resulted in the appearance of the 12₂ factor—these were interpreted to be defective in the enzyme(s) needed to synthesize the glucose-lipid intermediate that participates in both 12₂- 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 12₂ 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 12₂. The lesion in all the 12₂ 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 12₂ had been previously mapped. The results suggest the presence of a 12₂ glucosylation operon in this region.

¹ Dedicated to Otto Westphal on his 60th birthday.

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