Roles of the three Mycobacterium smegmatis katG genes for peroxide detoxification and isoniazid susceptibility

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The Mycobacterium smegmatis genome contains three katG sequences: katGI, katGII, and katGIII.
• Catalase-peroxidases are essential enzymes for bacterial survival against oxidative stress.

Purpose of the Study:

• To investigate the functional roles of the three katG genes in Mycobacterium smegmatis survival.
• To determine the contribution of KatGI and KatGII to hydrogen peroxide resistance during different growth phases.
• To assess the role of katG genes in isoniazid susceptibility.

Main Methods:

• Construction and analysis of gene disruptants for katGI, katGII, and katGIII in M. smegmatis.
• Measurement of peroxidase activity and mRNA expression levels.
• Assessment of susceptibility to hydrogen peroxide (H2O2) and isoniazid (INH) in wild-type and mutant strains across different growth phases.

Main Results:

• katGIII did not yield a functional catalase-peroxidase.
• Expression dominance between KatGI and KatGII switched between exponential and stationary phases.
• In the exponential phase, katGI-null strains showed increased H2O2 susceptibility, while in the stationary phase, katGII-null strains were more susceptible.
• katGI was identified as a major determinant of M. smegmatis susceptibility to isoniazid (INH).

Conclusions:

• Mycobacterium smegmatis possesses two functional catalase-peroxidases (KatGI and KatGII) with distinct roles and differential gene regulation.
• The expression of KatGI and KatGII is dynamically regulated, contributing to bacterial survival under oxidative stress during different growth phases.
• katGI plays a significant role in conferring isoniazid resistance in M. smegmatis.