Graham Christopher I, Patel Palak G, Tanner Jennifer R, Hellinga Jacqueline, MacMartin Teassa L, Hausner Georg, Brassinga Ann Karen C
Department of Microbiology, Faculty of Science, University of Manitoba, Winnipeg, MB, Canada.
Mol Microbiol. 2021 Aug;116(2):624-647. doi: 10.1111/mmi.14760. Epub 2021 Jun 12.
Legionella pneumophila possesses a unique intracellular lifecycle featuring distinct morphological stages that include replicative forms and transmissive cyst forms. Expression of genes associated with virulence traits and cyst morphogenesis is concomitant, and governed by a complex stringent response based-regulatory network and the stationary phase sigma factor RpoS. In Pseudomonas spp., rpoS expression is controlled by the autorepressor PsrA, and orthologs of PsrA and RpoS are required for cyst formation in Azotobacter. Here we report that the L. pneumophila psrA ortholog, expressed as a leaderless monocistronic transcript, is also an autorepressor, but is not a regulator of rpoS expression. Further, the binding site sequence recognized by L. pneumophila PsrA is different from that of Pseudomonas PsrA, suggesting a repertoire of target genes unique to L. pneumophila. While PsrA was dispensable for growth in human U937-derived macrophages, lack of PsrA affected bacterial intracellular growth in Acanthamoeba castellanii protozoa, but also increased the quantity of poly-3-hydroxybutyrate (PHB) inclusions in matured transmissive cysts. Interestingly, overexpression of PsrA increased the size and bacterial load of the replicative vacuole in both host cell types. Taken together, we report that PsrA is a host-specific requirement for optimal temporal progression of L. pneumophila intracellular lifecycle in A. castellanii.
嗜肺军团菌具有独特的细胞内生命周期，其特征在于包括复制形式和传播性囊肿形式在内的不同形态阶段。与毒力特征和囊肿形态发生相关的基因表达是同时发生的，并受基于严格反应的复杂调控网络和稳定期σ因子RpoS的控制。在假单胞菌属中，rpoS的表达受自身抑制因子PsrA的控制，并且在固氮菌中囊肿形成需要PsrA和RpoS的直系同源物。在这里，我们报告嗜肺军团菌的psrA直系同源物以无 leader 的单顺反子转录本形式表达，它也是一种自身抑制因子，但不是rpoS表达的调节因子。此外，嗜肺军团菌PsrA识别的结合位点序列与假单胞菌PsrA的不同，这表明嗜肺军团菌有一套独特的靶基因。虽然PsrA对于在人U937衍生的巨噬细胞中生长是可有可无的，但缺乏PsrA会影响细菌在卡氏棘阿米巴原虫中的细胞内生长，但也会增加成熟传播性囊肿中聚 - 3 - 羟基丁酸酯（PHB）包涵体的数量。有趣的是，PsrA的过表达增加了两种宿主细胞类型中复制泡的大小和细菌载量。综上所述，我们报告PsrA是嗜肺军团菌在卡氏棘阿米巴中细胞内生命周期最佳时间进程的宿主特异性需求。
