Department of Clinical Microbiology, Clinical Bacteriology, Umeå University, Sweden.
BMC Microbiol. 2012 Jan 21;12:14. doi: 10.1186/1471-2180-12-14.
The Francisella tularensis protein MglA performs complex regulatory functions since it influences the expression of more than 100 genes and proteins in F. tularensis. Besides regulating the igl operon, it has been suggested that it also regulates several factors such as SspA, Hfq, CspC, and UspA, all important to stress adaptation. Therefore, it can be hypothesized that MglA plays an important role for Francisella stress responses in general and for the oxidative stress response specifically.
We investigated the oxidative stress response of the ΔmglA mutant of the live vaccine strain (LVS) of F. tularensis and found that it showed markedly diminished growth and contained more oxidized proteins than the parental LVS strain when grown in an aerobic milieu but not when grown microaerobically. Moreover, the ΔmglA mutant exhibited an increased catalase activity and reduced expression of the fsl operon and feoB in the aerobic milieu. The mutant was also found to be less susceptible to H(2)O(2). The aberrant catalase activity and gene expression was partially normalized when the ΔmglA mutant was grown in a microaerobic milieu.
Altogether the results show that the ΔmglA mutant exhibits all the hallmarks of a bacterium subjected to oxidative stress under aerobic conditions, indicating that MglA is required for normal adaptation of F. tularensis to oxidative stress and oxygen-rich environments.
弗朗西斯氏菌 MglA 蛋白具有复杂的调控功能，因为它影响了弗朗西斯氏菌中超过 100 个基因和蛋白质的表达。除了调节 igl 操纵子，它还被认为调节了 SspA、Hfq、CspC 和 UspA 等几个因子，这些因子对适应应激都很重要。因此，可以假设 MglA 对弗朗西斯氏菌的应激反应，特别是对氧化应激反应，起着重要作用。
我们研究了弗朗西斯氏菌活疫苗株（LVS）ΔmglA 突变体的氧化应激反应，发现它在有氧环境中生长时，生长明显减缓，氧化蛋白含量高于亲本 LVS 株，而在微氧环境中生长时则没有。此外，ΔmglA 突变体在有氧环境中表现出更高的过氧化氢酶活性和降低的 fsl 操纵子和 feoB 的表达。该突变体对 H2O2 的敏感性也降低。当 ΔmglA 突变体在微氧环境中生长时，异常的过氧化氢酶活性和基因表达部分得到了正常化。
总之，这些结果表明，ΔmglA 突变体表现出了在有氧条件下受到氧化应激的细菌的所有特征，表明 MglA 是弗朗西斯氏菌适应氧化应激和富氧环境所必需的。
