Distinct Spatiotemporal Dynamics of Peptidoglycan Synthesis between Mycobacterium smegmatis and Mycobacterium tuberculosis

Peptidoglycan (PG), a polymer cross-linked by D-amino acid-containing peptides, is an essential component of the bacterial cell wall. We found that a fluorescent D-alanine analog (FDAA) incorporates chiefly at one of the two poles in Mycobacterium smegmatis but that polar dominance varies as a function of the cell cycle in Mycobacterium tuberculosis: immediately after cytokinesis, FDAAs are incorporated chiefly at one of the two poles, but just before cytokinesis, FDAAs are incorporated comparably at both. These observations suggest that mycobacterial PG-synthesizing enzymes are localized in functional compartments at the poles and septum and that the capacity for PG synthesis matures at the new pole in M. tuberculosis. Deeper knowledge of the biology of mycobacterial PG synthesis may help in discovering drugs that disable previously unappreciated steps in the process. IMPORTANCE People are dying all over the world because of the rise of antimicrobial resistance to medicines that could previously treat bacterial infections, including tuberculosis. Here, we used fluorescent D-alanine analogs (FDAAs) that incorporate into peptidoglycan (PG)-the synthesis of which is an attractive drug target-combined with high-and super-resolution microscopy to investigate the spatiotemporal dynamics of PG synthesis in M. smegmatis and M. tuberculosis. FDAA incorporation predominates at one of the two poles in M. smegmatis. In contrast, while FDAA incorporation into M. tuberculosis is also polar, there are striking variations in polar dominance as a function of the cell cycle. This suggests that enzymes involved in PG synthesis are localized in functional compartments in mycobacteria and that M. tuberculosis possesses a mechanism for maturation of the capacity for PG synthesis at the new pole. This may help in discovering drugs that cripple previously unappreciated steps in the process.