The prrAB Two-Component System Is Essential for Mycobacterium tuberculosis Viability and Is Induced under Nitrogen-Limiting Conditions

TheMycobacterium tuberculosis prrA-prrB (Rv0903c-Rv0902c) two-component regulatory system is expressed during intracellular growth in human macrophages and is required for early intracellular multiplication in murine macrophages, suggesting its importance in establishing infection. To better understand the function of theprrA-prrB two-component system, we defined the transcriptional characteristics of theprrA andprrB genes during exponential and stationary growth and upon exposure to different environmental stresses and attempted to generate aprrA-prrB deletion mutant. TheprrA andprrB genes constitute an operon and are cotranscribed during logarithmic growth, with transcriptional levels decreasing in stationary phase and during hypoxia. Despite the transcriptional differences, PrrA protein levels remained relatively stable throughout growth and in hypoxia. Under conditions of nitrogen limitation,prrAB transcription was induced, while acidic pH stress and carbon starvation did not significantly alter transcript levels. Deletion of theprrAB operon on the chromosome ofM. tuberculosis H37Rv occurred only in the presence of an episomal copy of theprrAB genes, indicating that this two-component system is essential for viability. Characterization of theprrAB locus inM. tuberculosis Mt21D3, a previously describedprrA transposon mutant, revealed that this strain is not a trueprrA knockout mutant. Rather, Tn5367 transposon insertion into theprrA promoter only decreasedprrA andprrB transcription and PrrA levels in Mt21D3 compared to those in the parental Mt103 clinical strain. These data provide the first report describing the essentiality of theM. tuberculosis prrAB two-component system and reveal insights into its potential role in mycobacterial growth and metabolism.