The marine bacterium Photobacterium damselae subsp. damselae (Pdd) causes disease in marine animals and humans. Previous studies demonstrated that mutation of the two-component system RstAB strongly impacts virulence of this pathogen, but the RstAB regulon has not been thoroughly elucidated. We here compared the transcriptomes of Pdd RM-71 and ΔrstA and ΔrstB derivatives using RNA-seq. In accordance with previous studies, RstAB positively regulated cytotoxins Dly, PhlyP and PhlyC. This analysis also demonstrated a positive regulation of outer membrane proteins, resistance against antimicrobials and potential virulence factors by this system. Remarkably, RstAB positively regulated two hitherto uncharacterised gene clusters involved in the synthesis of a polysaccharide capsule. Presence of a capsular layer in wild-type cells was confirmed by transmission electron microscopy, whereas rstA and rstB mutants were non-capsulated. Mutants for capsule synthesis genes, wza and wzc exhibited acapsular phenotypes, were impaired in resistance against the bactericidal action of fish serum and mucus, and were strongly impaired in virulence for fish, indicating a major role of capsule in virulence. Collectively, this study demonstrates that RstAB is a major positive regulator of key virulence factors including a polysaccharide capsule essential for full virulence in a pathogenic Photobacterium.

中文翻译：

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双组分系统 RstAB 调节多糖胶囊的产生，该多糖胶囊在海洋病原体 Photobacterium damselae subsp. 的毒力中起作用。少女

海洋细菌Photobacterium damselae subsp。damselae ( Pdd ) 导致海洋动物和人类疾病。先前的研究表明，双组分系统 RstAB 的突变强烈影响该病原体的毒力，但尚未彻底阐明 RstAB 调节子。我们在这里比较了Pdd RM-71 和 Δ rstA和 Δ rstB 的转录组使用RNA-seq的衍生物。根据之前的研究，RstAB 正向调节细胞毒素 Dly、PhlyP 和 PhlyC。该分析还证明了该系统对外膜蛋白、抗微生物剂和潜在毒力因子的正向调节。值得注意的是，RstAB 正向调节参与多糖荚膜合成的两个迄今未表征的基因簇。透射电子显微镜证实了野生型细胞中存在荚膜层，而rstA和rstB突变体没有被包裹。胶囊合成基因的突变体，wza和wzc表现出无荚膜表型，对鱼血清和粘液的杀菌作用的抵抗力受损，并且对鱼类的毒力严重受损，表明荚膜在毒力中的主要作用。总的来说，这项研究表明 RstAB 是关键毒力因子的主要正调节剂，包括对致病性光杆菌的完全毒力必不可少的多糖胶囊。