Transcriptome analysis was used to investigate the global stress response of the gram-positive bacterium Bacillus subtilis caused by overproduction of the well-secreted AmyQ alpha-amylase from Bacillus amyloliquefaciens. Analyses of the control and overproducing strains were carried out at the end of exponential growth and in stationary phase, when protein secretion from B. subtilis is optimal. Among the genes that showed increased expression were htrA and htrB, which are part of the CssRS regulon, which responds to high-level protein secretion and heat stress. The analysis of the transcriptome profiles of a cssS mutant compared to the wild type, under identical secretion stress conditions, revealed several genes with altered transcription in a CssRS-dependent manner, for example, citM, ylxF, yloA, ykoJ, and several genes of the flgB operon. However, high-affinity CssR binding was observed only for htrA, htrB, and, possibly, citM. In addition, the DNA macroarray approach revealed that several genes of the sporulation pathway are downregulated by AmyQ overexpression and that a group of motility-specific (sigmaD-dependent) transcripts were clearly upregulated. Subsequent flow-cytometric analyses demonstrate that, upon overproduction of AmyQ as well as of a nonsecretable variant of the alpha-amylase, the process of sporulation is severely inhibited. Similar experiments were performed to investigate the expression levels of the hag promoter, a well-established reporter for sigmaD-dependent gene expression. This approach confirmed the observations based on our DNA macroarray analyses and led us to conclude that expression levels of several genes involved in motility are maintained at high levels under all conditions of alpha-amylase overproduction.

译文

:转录组分析用于研究革兰氏阳性枯草芽孢杆菌的总体应激反应,该酶是由解淀粉芽孢杆菌分泌的大量分泌良好的AmyQα-淀粉酶引起的。当枯草芽孢杆菌的蛋白质分泌最适时,在指数生长结束时和在稳定期进行对照和高产菌株的分析。显示出增加表达的基因中有htrA和htrB,它们是CssRS regulon的一部分,对高水平的蛋白质分泌和热应激作出反应。在相同的分泌压力条件下,与野生型相比,cssS突变体的转录组图谱分析显示,一些基因以CssRS依赖性方式改变了转录,例如citM,ylxF,yloA,ykoJ和flgB操纵子。但是,仅对htrA,htrB和citM观察到高亲和力的CssR结合。此外,DNA宏阵列方法揭示了孢子形成途径的几个基因被AmyQ过表达下调,并且一组运动特异性(依赖sigmaD的)转录物明显上调。随后的流式细胞仪分析表明,当AmyQ以及α-淀粉酶的不可分泌变体过量生产时,孢子形成过程将受到严重抑制。进行了类似的实验,以研究hag启动子的表达水平,hag启动子是sigmaD依赖性基因表达的公认报告子。这种方法证实了基于我们的DNA宏阵列分析的观察结果,并导致我们得出结论,在所有α-淀粉酶过量生产的条件下,与运动相关的几个基因的表达水平均维持在较高水平。

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