The mycobacterial nucleoid-associated protein NapM exhibits stress-induced septal localization and modulates cell envelope gene expression

ABSTRACT The bacterial chromosome is organized in a hierarchical and dynamic manner to facilitate essential DNA transactions. Nucleoid-associated proteins (NAPs) are abundant, small-scale chromosomal organizers that also play important roles in maintaining chromosomal DNA integrity, regulating gene expression and DNA replication, and facilitating DNA repair. Here, we show that under optimal growth conditions, NapM—a unique mycobacterial NAP—modulates the expression of nearly one-sixth of M. smegmatis genes, with a notable impact on pathways involved in metabolism and cell envelope biosynthesis. Furthermore, we demonstrate that in response to cell-envelope-targeting agents, NapM localizes to the septum. Moreover, its absence contributes to the lower stability of septal DivIVA, a key component of the divisome, thereby ensuring accurate cell division under stress. Together, our findings suggest that NapM supports mycobacterial cell division by modulating the transcriptomic landscape and by associating with the divisome. These functions distinguish NapM from canonical nucleoid-associated proteins and prompt a re-evaluation of its functional classification. IMPORTANCE Understanding how bacteria adapt to environmental stress is critical to combating antibiotic resistance. This study characterizes NapM, a stress-responsive nucleoid-associated protein (NAP) in Mycobacterium smegmatis that couples maintenance of the transcriptional profile with the function of the cell division machinery. Distinct from canonical NAPs, NapM is essential for the proper expression of genes involved in metabolism and cell envelope biosynthesis. It also exhibits stress-dependent septal localization. This dual functionality reveals a unique adaptive strategy by which mycobacteria coordinate envelope maintenance and cytokinesis, advancing our understanding of bacterial stress resistance and identifying a potential target for therapeutic development.