Reversal of the growth inhibitory action of glycine and glycylglycine by alanylalanine in Mycobacterium smegmatis

Inhibition of growth of Mycobacterium smegmatis and of cell wall synthesis by D-serine

d-Serine inhibited the growth of Mycobacterium smegmatis and induced the morphological alteration of the bacilli. The growth inhibitory action of d-serine was partially reduced by an equimolecular concentration of d-alanine. The combination of glycine with d-alanine reversed the growth inhibition produced by d-serine more than did d-alanine alone. In cells cultured in the presence of d-serine, the amounts of alanine, diaminopimelic acid, and glycine inserted into the cell wall mucopeptide were reduced, and serine was increased. The intracellular accumulation of a precursor of cell wall mucopeptide was increased by d-serine, and this accumulation was reduced by d-alanine. d-Serine competed with glycine for incorporation into the cell wall mucopeptide. The incorporation of l-aspartic acid into diaminopimelic acid residues in the cell wall mucopeptide was markedly inhibited by d-serine. Three mutants resistant to d-serine were isolated by nitrosoguanidine treatment. In these mutants the effects of d-serine on the sites of cell wall mucopeptide synthesis were all reduced. Thus, d-serine inhibition of the growth is due to replacement of glycine residues of the cell wall mucopeptide with d-serine and inhibition of the cell wall synthesis by blocking the formation of d-alanine and diaminopimelic acid.

Gene manipulation in mycobacteria

Gene manipulation in mycobacteria developed in two phases. In the first phase genes of mycobacteria were transferred into cells of E. coli and Streptomyces lividans. In the second phase, heterologous genes were transferred into mycobacteria either with a shuttle plasmid or hybrid plasmids. A prerequisite for successful gene manipulation in mycobacteria was a thorough understanding of plasmids in mycobacteria. Construction of recombinant DNA molecules contributed not only to the fact that mycobacteria did not remain outside the mainstream of modern genetic research but also to their present practical importance.

Studies on Escherichia coli enzymes involved in the synthesis of uridine diphosphate-N-acetyl-muramyl-pentapeptide

The specific activities of l-alanine:d-alanine racemase, d-alanine:d-alanine ligase, and the l-alanine, d-glutamic acid, meso-diaminopimelic acid, and d-alanyl-d-alanine adding enzymes were followed during growth of Escherichia coli. The specific activities were nearly independent of the growth phase. d-Alanine:d-alanine ligase was inhibited by d-alanyl-d-alanine, d-cycloserine, glycine, and glycyl-glycine. l-Alanine:d-alanine racemase was found to be sensitive to d-cycloserine, glycine, and glycyl-glycine. The l-alanine adding enzyme was inhibited by glycine and glycyl-glycine.