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

ABSTRACT Three different katG sequences (katGI, katGII, and katGIII) were identified in the Mycobacterium smegmatis genome. The contribution of the three katG genes to survival of the bacterium was examined by constructing gene disruptants of these three genes. The katGIII sequence did not produce a functional catalase‐peroxidase. Analyses of peroxidase activity and mRNA expression revealed that in wild type M. smegmatis, expression dominance between KatGI and KatGII was switched in the exponential growth phase and the stationary growth phase. Susceptibility of the M. smegmatis gene disruptants to hydrogen peroxide (H2O2) was tested in the two growth phase. In the exponential phase, the katGI‐null strain was more susceptible to H2O2 than the katGII‐null strain, indicating that KatGI plays a more important role in survival than KatGII in this growth phase. On the contrary, in the stationary phase, growth of the katGII‐null strain was inhibited at lower concentrations of H2O2. These results suggest that M. smegmatis has two types of catalase‐peroxidases of which expressions are controlled under different gene regulatory systems. Isoniazid (INH) susceptibilities of the katG‐null strains were also examined. Analyses revealed the katGI to be a major determinant of INH susceptibility of M. smegmatis.
Source: Microbiology and Immunology - Category: Microbiology Authors: Tags: Original Article Source Type: research