Pre-Harvest Food Safety and Enteric Diseases Research Unit, National Animal Disease Center, Ames, IA 50010, USA.
Agroecosystems Management Research Unit, National Laboratory for Agriculture and the Environment, Agricultural Research Service, United States Department of Agriculture, Ames, IA 50010, USA.
Microbiology (Reading). 2010 May;156(Pt 5):1303-1312. doi: 10.1099/mic.0.034330-0. Epub 2010 Jan 28.
Quorum-sensing (QS) signalling pathways are important regulatory networks for controlling the expression of genes promoting adherence of enterohaemorrhagic Escherichia coli (EHEC) O157 : H7 to epithelial cells. A recent study has shown that EHEC O157 : H7 encodes a luxR homologue, called sdiA, which upon overexpression reduces the expression of genes encoding flagellar and locus of enterocyte effacement (LEE) proteins, thus negatively impacting on the motility and intimate adherence phenotypes, respectively. Here, we show that the deletion of sdiA from EHEC O157 : H7 strain 86-24, and from a hha (a negative regulator of ler) mutant of this strain, enhanced bacterial adherence to HEp-2 epithelial cells of the sdiA mutant strains relative to the strains containing a wild-type copy of sdiA. Quantitative reverse transcription PCR showed that the expression of LEE-encoded genes ler, espA and eae in strains with the sdiA deletions was not significantly different from that of the strains wild-type for sdiA. Similarly, no additional increases in the expression of LEE genes were observed in a sdiA hha double mutant strain relative to that observed in the hha deletion mutant. While the expression of fliC, which encodes flagellin, was enhanced in the sdiA mutant strain, the expression of fliC was reduced by several fold in the hha mutant strain, irrespective of the presence or absence of sdiA, indicating that the genes sdiA and hha exert opposing effects on the expression of fliC. The strains with deletions in sdiA or hha showed enhanced expression of csgA, encoding curlin of the curli fimbriae, with the expression of csgA highest in the sdiA hha double mutant, suggesting an additive effect of these two gene deletions on the expression of csgA. No significant differences were observed in the expression of the genes lpfA and fimA of the operons encoding long polar and type 1 fimbriae in the sdiA mutant strain. These data indicate that SdiA has no significant effect on the expression of LEE genes, but that it appears to act as a strong repressor of genes encoding flagella and curli fimbriae, and the alleviation of the SdiA-mediated repression of these genes in an EHEC O157 : H7 sdiA mutant strain contributes to enhanced bacterial motility and increased adherence to HEp-2 epithelial cells.
群体感应（QS）信号通路是控制促进肠出血性大肠杆菌（EHEC）O157：H7 附着上皮细胞的基因表达的重要调控网络。最近的一项研究表明，EHEC O157：H7 编码一个 luxR 同源物，称为 sdiA，其过表达降低了编码鞭毛和肠上皮细胞消失（LEE）蛋白的基因的表达，从而分别对运动性和紧密附着表型产生负面影响。在这里，我们表明，从 EHEC O157：H7 菌株 86-24 中删除 sdiA，以及从该菌株的 hha（ler 的负调节剂）突变体中删除 sdiA，增强了 sdiA 突变菌株相对于含有野生型 sdiA 菌株的细菌对 HEp-2 上皮细胞的附着。定量逆转录 PCR 显示，sdiA 缺失菌株中 LEE 编码基因 ler、espA 和 eae 的表达与 sdiA 野生型菌株没有显著差异。同样，在 sdiA hha 双突变体菌株中观察到的 LEE 基因表达的额外增加与在 hha 缺失突变体菌株中观察到的增加没有显著差异。虽然 sdiA 突变菌株中 fliC（编码鞭毛蛋白）的表达增强，但 hha 突变菌株中 fliC 的表达降低了几个数量级，无论是否存在 sdiA，这表明 sdiA 和 hha 基因对 fliC 的表达产生相反的影响。sdiA 或 hha 缺失的菌株表现出 curlin（卷曲菌毛的卷曲蛋白）编码基因 csgA 的表达增强，sdiA hha 双突变体中 csgA 的表达最高，表明这两个基因缺失对 csgA 的表达有累加效应。sdiA 突变菌株中编码长极性和 1 型菌毛的 operons 的 lpfA 和 fimA 基因的表达没有显著差异。这些数据表明，SdiA 对 LEE 基因的表达没有显著影响，但它似乎作为鞭毛和卷曲菌毛编码基因的强烈抑制剂，并且在 EHEC O157：H7 sdiA 突变体中减轻 SdiA 介导的这些基因的抑制有助于增强细菌的运动性并增加对 HEp-2 上皮细胞的附着。
