Properties of a D-glutamic acid-requiring mutant of Escherichia coli

Abstract

Some properties of a d-glutamic acid auxotroph of Escherichia coli B were studied. The mutant cells lysed in the absence of d-glutamic acid. Murein synthesis was impaired, accompanied by accumulation of uridine-5'-diphosphate-N-acetyl-muramyl-l-alanine (UDP-MurNac-l-Ala), as was shown by incubation of the mutant cells in a cell wall medium containing l-[(14)C]alanine. After incubation of the parental strain in a cell wall medium containing l-[(14)C]glutamic acid, the acid-precipitable radioactivity was lysozyme degradable to a large extent. Radioactive UDP-MurNac-pentapeptide was isolated from the l-[(14)C]glutamic acid-labeled parental cells. After hydrolysis, the label was exclusively present in glutamic acid, the majority of which had the stereo-isomeric d-configuration. Compared to the parent the mutant incorporated less l-[(14)C]glutamic acid from the wall medium into acid-precipitable material. Lysozyme degraded a smaller percentage of the acid-precipitable material of the mutant than of that of the parent. No radioactive uridine nucleotide precursors could be isolated from the mutant under these conditions. Attempts to identify the enzymatic defect in this mutant were not successful. The activity of UDP-MurNac-l-Ala:d-glutamic acid ligase (ADP; EC 6.3.2.9) (d-glutamic acid adding enzyme) is not affected by the mutation. Possible pathways for d-glutamic acid biosynthesis in E. coli B are discussed.