The PhoPR system is a master regulator in Mycobacterium tuberculosis. A key difference between M. tuberculosis and Mycobacterium bovis is a G71I substitution in the M. bovis PhoR orthologue. Functional studies of the M. bovis PhoPR system have generated conflicting findings, with some research suggesting that the M. bovis PhoPR is defective while others indicate it is functional.

We sought to revisit the functionality of the M. bovis PhoPR system. To address this, we constructed a phoPR mutant in the reference strain M. bovis AF2122/97. We employed a combination of growth assays and transcriptomics analyses to assess the phenotype of the mutant vs wild type and complemented strains. We found that the M. bovis AF2122/97 ΔphoPR mutant showed a growth defect on solid and liquid media compared to the wild type and complemented strains. The transcriptome of the M. bovis AF2122/97 ΔphoPR mutant was also altered as compared to wild type, including differential expression of genes involved in lipid metabolism and secretion. Our work provides further insight into the activity of PhoPR in M. bovis and underlines the importance of the PhoPR system as a master regulator of gene expression in the Mycobacterium tuberculosis complex.