Laboratory of Bacterial Genetics, School of Biotechnology, Faculty of Science, Banaras Hindu University, Varanasi-221005, India.
National Botanical Research Institute, Rana Pratap Marg, Lucknow-226001, India.
Microbiology (Reading). 2012 Dec;158(Pt 12):2891-2902. doi: 10.1099/mic.0.062380-0. Epub 2012 Sep 28.
Bacteria belonging to the Alphaproteobacteria normally harbour multiple copies of the heat shock sigma factor (known as σ(32), σ(H) or RpoH). Azospirillum brasilense, a non-photosynthetic rhizobacterium, harbours five copies of rpoH genes, one of which is an rpoH2 homologue. The genes around the rpoH2 locus in A. brasilense show synteny with that found in rhizobia. The rpoH2 of A. brasilense was able to complement the temperature-sensitive phenotype of the Escherichia coli rpoH mutant. Inactivation of rpoH2 in A. brasilense results in increased sensitivity to methylene blue and to triphenyl tetrazolium chloride (TTC). Exposure of A. brasilense to TTC and the singlet oxygen-generating agent methylene blue induced several-fold higher expression of rpoH2. Comparison of the proteome of A. brasilense with its rpoH2 deletion mutant and with an A. brasilense strain overexpressing rpoH2 revealed chaperone GroEL, elongation factors (Ef-Tu and EF-G), peptidyl prolyl isomerase, and peptide methionine sulfoxide reductase as the major proteins whose expression was controlled by RpoH2. Here, we show that the RpoH2 sigma factor-controlled photooxidative stress response in A. brasilense is similar to that in the photosynthetic bacterium Rhodobacter sphaeroides, but that RpoH2 is not involved in the detoxification of methylglyoxal in A. brasilense.
属于α变形菌的细菌通常拥有多个热休克σ因子（称为σ(32)、σ(H)或 RpoH）的拷贝。非光合根瘤菌 Azospirillum brasilense 拥有 5 个 rpoH 基因拷贝，其中一个是 rpoH2 同源物。A. brasilense 中 rpoH2 基因座周围的基因与根瘤菌中的基因具有同线性。A. brasilense 的 rpoH2 能够补充大肠杆菌 rpoH 突变体的温度敏感表型。A. brasilense 中 rpoH2 的失活导致对亚甲基蓝和三苯基四氮唑氯化物（TTC）的敏感性增加。A. brasilense 暴露于 TTC 和单线态氧生成剂亚甲基蓝会诱导 rpoH2 表达增加几倍。将 A. brasilense 的蛋白质组与其 rpoH2 缺失突变体和过表达 rpoH2 的 A. brasilense 菌株进行比较，发现伴侣蛋白 GroEL、延伸因子（Ef-Tu 和 EF-G）、肽基脯氨酰顺反异构酶和肽甲硫氨酸亚砜还原酶是受 RpoH2 控制表达的主要蛋白质。在这里，我们表明 RpoH2 σ因子控制的 A. brasilense 光氧化应激反应类似于光合细菌 Rhodobacter sphaeroides，但 RpoH2 不参与 A. brasilense 中甲基乙二醛的解毒。
