A New Class of Heptose‐Defective Mutant of Salmonella typhimurium

Publisher Website
Google Scholar
Abstract
Salmonella typhimurium rfa‐657 strains, including both mutants and transductants, were shown to contain in their lipopolysaccharides both the (usual) l and the d‐isomer of glycero‐d‐manno‐heptose. By the application, in sequence, of two different extraction procedures S and R form lipopolysaccharides could be isolated separately from a representative rfa‐657 strain. The R lipopolysaccharide was predominantly of the Re chemotype, only a few 2‐keto‐3‐deoxyoctonate (KDO) residues being substituted by heptose (Rd2 chemotype) or by longer core chains. The d‐heptose was enriched in the R lipopolysaccharide, while the S lipopolysaccharide contained mainly the natural l‐isomer. It was found that d‐heptose can replace l‐heptoses I to III of the wild‐type core. However, an elongation to completeness of the core stubs containing d‐heptose seldom occurs.The heterogeneity in structure of the lipopolysaccharide produced by this class of (leaky) mutants is assumed to be due to an altered 6‐epimerase which, in the wild form, catalyses the conversion of NDP‐d‐glycero‐d‐manno‐heptose into NDP‐l‐glycero‐d‐manno‐heptose and which is determined by the gene rfa‐657 situated between cysE and pyrE. The symbol rfaD is proposed for this gene.