Uhlich Gaylen A
Microbial Food Safety Research Unit, Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, PA, USA.
Microbiology (Reading). 2009 Nov;155(Pt 11):3589-3598. doi: 10.1099/mic.0.031435-0. Epub 2009 Aug 27.
Escherichia coli K-12 defends itself against peroxide-mediated oxidative damage using two catalases, KatG and KatE, and the peroxiredoxin, alkyl hydroperoxide reductase, encoded by ahpC. In E. coli O157 : H7 strain ATCC 43895 (EDL933), plasmid pO157 carries an additional catalase-peroxidase gene, katP. KatP has been shown to be a functional catalase-peroxidase. However, deletion of pO157 does not alter the peroxide resistance of strain EDL933, leaving the physiological role of katP unclear. To examine the individual roles of peroxide-resistance genes in E. coli O157 : H7, mutant strains of ATCC 43895 were constructed bearing individual deletions of katG, katE, katP and ahpC, as well as double, triple and quadruple deletions encompassing all possible gene combinations thereof. The wild-type and all 15 mutant strains were compared for differences in aerobic growth, ability to scavenge exogenous H(2)O(2) and resistance to exogenous peroxides. Although KatG scavenged the most exogenous H(2)O(2), KatP scavenged statistically greater amounts than either KatE or AhpC during exponential growth. However, katG and ahpC together were sufficient for full peroxide resistance in disc diffusion assays. Strains with only katG or ahpC were the only triple deletion strains with significantly shorter generation times than the quadruple deletion strain. ahpC was the only gene that could allow rapid transition from lag phase to exponential phase in a triple deletion strain. Gene expression studies revealed that katP is an OxyR-regulated gene, but its expression is suppressed in stationary phase by RpoS. These studies indicate that pO157-borne katP contributes to the complex gene network protecting strain 43895 from peroxide-mediated oxidative damage in an OxyR-dependent manner.
大肠杆菌K-12利用两种过氧化氢酶KatG和KatE以及由ahpC编码的过氧化物还原酶（烷基过氧化氢还原酶）来抵御过氧化物介导的氧化损伤。在大肠杆菌O157:H7菌株ATCC 43895（EDL933）中，质粒pO157携带一个额外的过氧化氢酶-过氧化物酶基因katP。KatP已被证明是一种功能性过氧化氢酶-过氧化物酶。然而，缺失pO157并不会改变EDL933菌株的过氧化物抗性，这使得katP的生理作用尚不清楚。为了研究过氧化物抗性基因在大肠杆菌O157:H7中的各自作用，构建了ATCC 43895的突变菌株，这些菌株分别缺失katG、katE、katP和ahpC，以及包含所有可能基因组合的双缺失、三缺失和四缺失菌株。比较了野生型和所有15种突变菌株在有氧生长、清除外源H₂O₂的能力以及对外源过氧化物的抗性方面的差异。虽然KatG清除的外源H₂O₂最多，但在指数生长期，KatP清除的量在统计学上比KatE或AhpC都要多。然而，在纸片扩散试验中，katG和ahpC共同作用足以实现完全的过氧化物抗性。仅缺失katG或ahpC的菌株是仅有的三缺失菌株，其代时明显短于四缺失菌株。ahpC是唯一能使三缺失菌株从延滞期快速过渡到指数期的基因。基因表达研究表明，katP是一个受OxyR调控的基因，但其表达在稳定期被RpoS抑制。这些研究表明，pO157携带的katP以依赖OxyR的方式对保护43895菌株免受过氧化物介导的氧化损伤的复杂基因网络有贡献。
