Biochemistry of the K Antigens of Escherichia coli

Initial work on the determination of the mechanisms of the biosynthesis of the K antigens of E. coli is described. Mutants defective in the biosynthesis of the K‐polysaccharide were used for this study. Acapsular K– mutants were isolated from E. coli 08:K27(A):H– and characterized serologically and through their sensitivity towards specific phages. Previous studies have shown the K27 antigen to be an acidic polysaccharide consisting of glucuronic acid, glucose, galactose and l‐fucose. The 08‐antigen contains mannose as the main constituent of its specific polysaccharide moiety. The influence of mutation on the biosynthetic pathways leading to the K27 polysaccharide was investigated. For this purpose wild strain and various K– mutants were analyzed in this study for the presence of enzymes catalyzing the synthesis of the nucleotide sugar precursors: UDP‐glucose, UDP‐galactose, UDP‐glucuronic acid, GDP‐mannose and GDP‐l‐fucose. The following bacterial enzyme activities were tested in cell free system: hexokinase, phosphoglucoisomerase, phosphoglucomutase, UDP‐glucose pyrophosphorylase, UDP‐galactose‐4‐epimerase, UDP‐glucose dehydrogenase, GDP‐mannose pyrophosphorylase, GDP‐mannose hydrolyase. When two K– mutants were crossed and selections were made for his+, a small but significant number of K+ strains appeared among the recombinants. Thus, it was concluded that the parent K– strains had different blocks in the synthesis of the K27 antigen which mapped at different sites on the chromosome. Repair occurred due to crossing over within a small (his‐linked) region of the chromosome. Biochemically, the repair of the K– character by genetic crossing of the two K– mutants was reflected in the capability for GDP‐l‐fucose synthesis which was deficient in the donor strain as well as in the larger portion of the K– recombinants. In two of the K– mutants all enzymes tested were found to be operative. Since synthesis of the nucleotide precursors was possible, these mutants probably have a defect in the K27 specific transferase system. One K– mutant, which serves as the recipient in the genetic crossing, showed some serological R character. This mutant possessed a very low GDP‐mannose pyrophosphorylase activity; however, some O specific (mannose containing) polysaccharide was formed. Since all other synthetases are active in this mutant it is assumed that also in this case the K27 transferase system may be defective.