A Role for Mycobacterium tuberculosis Sigma Factor C in Copper Nutritional Immunity

Area of Science:

• Microbiology
• Molecular Biology
• Tuberculosis Research

Background:

• Sigma factor C (SigC) is implicated in Mycobacterium tuberculosis virulence.
• The specific stress response regulated by SigC remained undefined.
• Understanding SigC's role is crucial for combating tuberculosis.

Purpose of the Study:

• To elucidate the stress response coordinated by Sigma factor C (SigC) in Mycobacterium tuberculosis.
• To investigate SigC's role in copper homeostasis and acquisition.
• To determine SigC's contribution to bacterial virulence under copper-limiting conditions.

Main Methods:

• Whole genome expression studies (transcriptomics) using tetracycline-inducible promoter system.
• Growth assays in standard and copper-deficient media.
• Analysis of SigC deletion mutants in vitro and in vivo (SCID mice).

Main Results:

• SigC upregulates copper acquisition genes (ctpB, nrp operon) under short-term induction.
• Prolonged SigC induction leads to excessive copper uptake.
• SigC deletion mutants exhibit growth defects in copper-deficient media, which are reversed by copper supplementation.
• SigC mutants show attenuated virulence in SCID mice, suggesting impaired copper acquisition.

Conclusions:

• SigC acts as a transcriptional regulator of copper acquisition in Mycobacterium tuberculosis, particularly under conditions of copper scarcity.
• SigC is essential for overcoming host defenses that sequester copper.
• Targeting SigC may represent a novel therapeutic strategy against tuberculosis.