Lipopolysaccharide heterogeneity in Escherichia coli J5 variants: analysis by flow cytometry

A lipopolysaccharide O-side chain-producing phenotypic variant was isolated from a uridine 5'-diphosphogalactose 4-epimeraseless Escherichia coli J5 rough mutant strain by fluorescence-activated cell sorting with a monoclonal antibody (MAb) specific for the O-side chain of E. coli O111:B4 smooth parent lipopolysaccharide. The variant (J5-2) was recognized by both core- and O-side chain-specific MAbs, while the "original" rough mutant (J5-1) and smooth parent strains stained only with core- and O-side chain-specific MAb, respectively. J5-2 produced complete and incomplete (Rc chemotype) core and O polysaccharide in the presence of galactose. Three other E. coli J5 variants were either phenotypically similar to J5-1 (J5-UK) or distinct from J5-1 and J5-2 (J5-A, -B). The latter phenotype had a lower-molecular-weight core, compared with J5-1 and J5-2, and distinct MAb specificities. Various J5 phenotypes also differed in galactokinase levels, the ability to use galactose, and susceptibility to core-specific MAb binding on solid media. The J5-2 strain showed reciprocal changes in O-side chain and core expression during log-phase growth. E. coli J5 thus undergoes spontaneous alterations in lipopolysaccharide phenotype.