Phosphate depletion: a novel trigger for Mycobacterium tuberculosis persistence.

Area of Science:

• Microbiology
• Molecular Biology
• Infectious Diseases

Background:

• Persistent Mycobacterium tuberculosis (MTB) likely faces phosphate-limited conditions within macrophage phagosomes.
• Understanding MTB's adaptation to nutrient-scarce environments is critical for developing effective treatments.

Purpose of the Study:

• To investigate the impact of phosphate limitation on MTB growth, antibiotic susceptibility, and gene expression.
• To identify key genes and regulatory pathways involved in MTB's phosphate starvation response (PSR).

Main Methods:

• Culturing MTB under varying phosphate concentrations and assessing growth and survival.
• Evaluating antibiotic susceptibility of phosphate-starved MTB.
• Analyzing gene expression patterns using quantitative PCR and analyzing MTB mutants in vivo.

Main Results:

• Phosphate limitation dose-dependently restricted MTB growth and induced phenotypic tolerance to isoniazid.
• Phosphate starvation upregulated MTB genes ppk1 and relA, indicating inorganic polyphosphate accumulation and stringent response.
• The pst operon (pstS3-pstC2-pstA1) and the SenX3-RegX3 regulatory system were induced, with regX3 being essential for survival in phosphate-limited conditions and mammalian lungs.

Conclusions:

• MTB encounters phosphate-limited environments during mammalian lung infection.
• The phosphate starvation response (PSR) pathway, particularly the regX3 gene, is vital for MTB persistence in vivo.
• Targeting the PSR pathway could be a novel strategy against persistent tuberculosis infections.