Isolation of a mutant from Salmonella typhimurium producing acyl‐deficient lipopolysaccharides

The present paper describes the isolation and characterization of a mutant (mutant Ts7) of Salmonella typhimurium that is conditionally defective in the incorporation of dodecanoic and tetradecanoic acid into lipopolysaccharide precursor structures. Enrichment of mutant Ts7 was achieved by free-flow electrophoresis and was based on a previous observation that at least some Salmonella mutants conditionally blocked in the synthesis of the 3-deoxy-D-manno-octulosonic acid (dOclA)–lipid-A region exhibit higher electrophoretic mobilities than cells with intact dOclA–lipid-A regions. Under nonpermissive conditions (42°C) mutant Ts7 accumulates at least two incomplete dOclA–lipid-A structures. One is made up of glucosamine, phosphate, dOclA, and 3-hydroxytetradecanoic acid in a molar ratio 1.0:1.3:1.0:2.2 and is devoid of dodecanoic and tetradecanoic acid. The other structure has the same basic structure but contains hexadecanoic acid.