Aberg Anna, Shingler Victoria, Balsalobre Carlos
Department of Molecular Biology, Umeå University, S-90187 Umeå, Sweden.
Mol Microbiol. 2006 Jun;60(6):1520-33. doi: 10.1111/j.1365-2958.2006.05191.x.
In this report we have examined the role of the regulatory alarmone (p)ppGpp on expression of virulence determinants of uropathogenic Escherichia coli strains. The ability to form biofilms is shown to be markedly diminished in (p)ppGpp-deficient strains. We present evidence (i) that (p)ppGpp tightly regulates expression of the type 1 fimbriae in both commensal and pathogenic E. coli isolates by increasing the subpopulation of cells that express the type 1 fimbriae; and (ii) that the effect of (p)ppGpp on the number of fimbrial expressing cells can ultimately be traced to its role in transcription of the fimB recombinase gene, whose product mediates inversion of the fim promoter to the productive (ON) orientation. Primer extension analysis suggests that the effect of (p)ppGpp on transcription of fimB occurs by altering the activity of only one of the two fimB promoters. Furthermore, spontaneous mutants with properties characteristic of ppGpp(0) suppressors restore fimB transcription and consequent downstream effects in the absence of (p)ppGpp. Consistently, the rpoB3770 allele also fully restores transcription of fimB in a ppGpp(0) strain and artificially elevated levels of FimB bypass the need for (p)ppGpp for type 1 fimbriation. Our findings suggest that the (p)ppGpp-stimulated expression of type 1 fimbriae may be relevant during the interaction of pathogenic E. coli with the host.
在本报告中，我们研究了调节警报素（p）ppGpp对尿路致病性大肠杆菌菌株毒力决定因素表达的作用。结果表明，（p）ppGpp缺陷型菌株形成生物膜的能力显著降低。我们提供的证据如下：（i）（p）ppGpp通过增加表达1型菌毛的细胞亚群，紧密调节共生和致病性大肠杆菌分离株中1型菌毛的表达；（ii）（p）ppGpp对菌毛表达细胞数量的影响最终可追溯到其在fimB重组酶基因转录中的作用，该基因的产物介导fim启动子向有活性（开启）方向的倒置。引物延伸分析表明，（p）ppGpp对fimB转录的影响仅通过改变两个fimB启动子之一的活性来实现。此外，具有ppGpp（0）抑制子特性的自发突变体在没有（p）ppGpp的情况下恢复fimB转录及随后的下游效应。一致地，rpoB3770等位基因也能在ppGpp（0）菌株中完全恢复fimB的转录，并且人为提高FimB的水平可绕过对（p）ppGpp进行1型菌毛形成的需求。我们的研究结果表明，（p）ppGpp刺激的1型菌毛表达可能在致病性大肠杆菌与宿主相互作用期间具有相关性。
