Legionella pneumophila (Lp) is a waterborne bacterium able to infect human alveolar macrophages, causing Legionnaires’ disease. Lp can survive for several months in water, while searching for host cells to grow in, such as ciliates and amoeba. In Lp, the sigma factor RpoS is essential for survival in water. A previous transcriptomic study showed that RpoS positively regulates the small regulatory RNA Lpr10. In the present study, deletion of lpr10 results in an increased survival of Lp in water. Microarray analysis and RT‐qPCR revealed that Lpr10 negatively regulates the expression of RpoS in the postexponential phase. Electrophoretic mobility shift assay and in‐line probing showed that Lpr10 binds to a region upstream of the previously identified transcription start sites (TSS) of rpoS. A third putative transcription start site was identified by primer extension analysis, upstream of the Lpr10 binding site. In addition, nlpD TSS produces a polycistronic mRNA including the downstream gene rpoS, indicating a fourth TSS for rpoS. Our results suggest that the transcripts from the third and fourth TSS are negatively regulated by the Lpr10 sRNA. Therefore, we propose that Lpr10 is involved in a negative regulatory feedback loop to maintain expression of RpoS to an optimal level.

中文翻译：

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小调节 RNA Lpr10 调节嗜肺军团菌中 RpoS 的表达

嗜 肺军团菌( Lp ) 是一种水传播细菌，能够感染人类肺泡巨噬细胞，导致军团病。Lp可以在水中存活数月，同时寻找宿主细胞生长，如纤毛虫和变形虫。在Lp 中，σ 因子 RpoS 对于在水中的生存至关重要。先前的转录组学研究表明，RpoS 正调节小调节 RNA Lpr10。在本研究中，lpr10 的缺失导致Lp 的存活率增加在水里。微阵列分析和 RT-qPCR 显示 Lpr10 在指数后阶段​​负调节 RpoS 的表达。电泳迁移率变化测定和在线探测表明 Lpr10 与先前确定的rpoS转录起始位点 (TSS) 上游的区域结合。第三个假定的转录起始位点是通过引物延伸分析确定的，位于 Lpr10 结合位点的上游。此外，nlpD启动TSS产生多顺反子的mRNA包括下游基因的rpoS，指示用于四分之一TSS的rpoS. 我们的结果表明，来自第三个和第四个 TSS 的转录本受到 Lpr10 sRNA 的负调控。因此，我们建议 Lpr10 参与负调节反馈回路，以将 RpoS 的表达维持在最佳水平。