Transcriptional control of asparagine utilization regulates mycobacterial pH-driven adaptation at the host-pathogen crossroads.

Mycobacterium tuberculosis, an intracellular pathogen, survives within the membrane-bound vacuole, the phagosome, with acidic pH and limited access to nutrients. To survive and replicate within the human host, M. tuberculosis must adapt and fulfil its nutritional requirements. To investigate how the intracellular bacillus scavenges nutrients from its host, we studied mycobacterial acquisition of host-derived amino acids, the preferred nitrogen sources. We discovered that PhoP, a key determinant of mycobacterial adaptation to phagosomal acidification, controls expression of AnsP1 and AnsP2 to facilitate acquisition of host aspartate and asparagine, respectively. Thus, macrophage-infected WT-H37Rv showed a significantly higher level of intra-bacterial Asn compared to the phoPR-KO mutant, and a complemented mutant could restore Asn levels to those of WT-H37Rv. Under acidic conditions, elevated DNA binding of PhoP within the promoters leads to direct activation of ansP1 and ansP2. Consistently, phoPR-KO is unable to utilize Asn under acidic conditions, and overexpression of ansP1 or ansP2 in the mutant restored the intracellular growth defect of the mutant. These findings uncover the regulatory network allowing utilization of organic nitrogen sources by the pathogen during infection.