The Alanine Racemase of Mycobacterium smegmatis Is Essential for Growth in the Absence of d-Alanine▿ †

Alanine racemase, encoded by the gene alr , is an important enzyme in the synthesis of d -alanine for peptidoglycan biosynthesis. Strains of Mycobacterium smegmatis with a deletion mutation of the alr gene were found to require d -alanine for growth in both rich and minimal media. This indicates that alanine racemase is the only source of d -alanine for cell wall biosynthesis in M. smegmatis and confirms alanine racemase as a viable target gene for antimycobacterial drug development.