Arginine and pyrimidine biosynthetic defects in Neisseria gonorrhoeae strains isolated from patients

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Abstract
N. gonorrhoeae strains with nutritional requirements that include arginine (Arg-), uracil (Ura-) and hypoxanthine have attracted attention because of their tendency to cause disseminated infections. As a basis for genetic studies of arginine and pyrimidine biosynthesis, the activities of 4 enzymes of these pathways was examined in cell-free extracts of both prototrophic and Arg- Ura- strains. Activities of glutamate acetyltransferase, aspartate transcarbamylase and orotate phosphoribosyltransferase, encoded respectively by argE, pyrB and pyrE, were absent in some Arg- Ura- isolates. Gonococci that were unable to utilize ornithine for growth in place of citrulline lacked activity of carbamyl phosphate synthetase (encoded by car). Defects of car imposed requirements for both citrulline (or arginine) and a pyrimidine because of the dual role of carbamyl phosphate in the 2 pathways. Defects of argE, car, pyrB and pyrE were separately introduced by genetic transformation into representatives of a gonococcal strain which initially was prototrophic. Results of enzyme assays of these isogenic auxotrophic transformants confirmed the gene-enzyme relationships.