Iwao Yasuhisa, Nakata Noboru
Department of Mycobacteriology, Leprosy Research Center, National Institute of Infectious Diseases, 4-2-1 Aoba-cho, Higashimurayama, Tokyo 189-0002, Japan.
Antimicrobial Resistance Research Center, National Institute of Infectious Diseases, 4-2-1 Aoba-cho, Higashimurayama, Tokyo 189-0002, Japan.
Microbiol Immunol. 2018 Mar;62(3):158-167. doi: 10.1111/1348-0421.12574.
Three different katG sequences (katGI, katGII and katGIII) were identified in the Mycobacterium smegmatis genome. The contributions of the three katG genes to survival of the bacterium were examined by constructing 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 and stationary growth phases. Susceptibility of the M. smegmatis gene disruptants to hydrogen peroxide (H O ) was tested in two growth phases. In the exponential phase, the katGI-null strain was more susceptible to H O than the katGII-null strain, indicating that KatGI plays a more important role in survival than KatGII in this growth phase. In contrast, in the stationary phase, growth of the katGII-null strain was inhibited at lower concentrations of H O . These results suggest that M. smegmatis has two types of catalase-peroxidases, expressions of which are controlled under different gene regulatory systems. Isoniazid (INH) susceptibilities of the katG-null strains were also examined and it was found that katGI is a major determinant of M. smegmatis susceptibility to INH.
在耻垢分枝杆菌基因组中鉴定出三种不同的katG序列（katGI、katGII和katGIII）。通过构建这三个基因的缺失突变体，研究了这三个katG基因对该细菌存活的贡献。katGIII序列不产生功能性过氧化氢酶-过氧化物酶。过氧化物酶活性和mRNA表达分析表明，在野生型耻垢分枝杆菌中，KatGI和KatGII之间的表达优势在指数生长期和稳定期发生了转换。在两个生长阶段测试了耻垢分枝杆菌基因缺失突变体对过氧化氢（H₂O₂）的敏感性。在指数生长期，katGI缺失菌株比katGII缺失菌株对H₂O₂更敏感，这表明在该生长阶段，KatGI在存活中比KatGII发挥更重要的作用。相反，在稳定期，较低浓度的H₂O₂即可抑制katGII缺失菌株的生长。这些结果表明，耻垢分枝杆菌有两种类型的过氧化氢酶-过氧化物酶，其表达受不同的基因调控系统控制。还检测了katG缺失菌株对异烟肼（INH）的敏感性，发现katGI是耻垢分枝杆菌对INH敏感性的主要决定因素。
