Properties of cysK mutants of Escherichia coli K12

Triazole and azaserine resistant mutants of E. coli K12 affecting cysK gene coding for O-acetylserine sulphydrylase were isolated. The cysK gene in E. coli is located in the same region of chromosome as the cycK gene in Salmonella typhimurium. All azaserine and some triazole resistant mutants require cysteine for growth at a normal rate. The cysK mutants have reduced sulphate uptake. Stability and transfer by conjugation of triazole resistant phenotype were checked. Differences in sulphate metabolism between closely related organisms E. coli and S. typhimurium are discussed.