The deacetylase NagA mediates the remodelling and recycling of peptidoglycan derived amino sugars in mycobacteria

Many bacterial species are known to recover peptidoglycan (PG) fragments released from remodelling of their cell walls during growth and cell division. These PG fragments not only provide an essential energy resource, especially in nutrient restricted environments, but also play a critical role in influencing infection. Yet whether mycobacteria have the capacity to recycle their PG, or not, has still not been resolved. In this study we show that NagA, an N-acetylglucosamine-6-phosphate (GlcNAc-6-P) deacetylase, is essential for coordinating the remodelling and recycling of an amino sugar component released from the mycobacterial cell wall. We show that NagA is exclusively responsible for GlcNAc-6-P deacetylation and is pivotal for the de novo synthesis of core cell wall building blocks. Indeed, a nagA deletion mutant exhibited an altered composition of the cell envelope, smaller overall cell size, defective biofilm formation, and enhanced susceptibility to cell wall targeting agents. Moreover, uptake analysis and profiling of the amino-sugar pool revealed that NagA inactivation blocks N-acetylglucosamine (GlcNAc) import and has a pronounced effect on the fate and levels of the intracellular amino sugar pool. Loss of NagA led to the up- and down-regulation of proteins involved in cell wall biosynthesis, thereby altering cell wall homeostasis. Overall, our data highlights the importance of an overlooked yet conserved component in an important PG salvage pathway in mycobacteria, in which NagA provides a unique GlcNAc sensing mechanism, thus acting as a checkpoint for regulating the recovery and reuse of PG fragments.