轉錄因子PsrA在調節綠膿桿菌（Pseudomonas aeruginosa）的第三型分泌系統、脂肪酸代謝和喹諾酮信號的群體感應系統中扮演著多方面的角色。本研究旨在進一步探討PsrA的功能，通過引入含有psrA基因（pMMBpsrA）的重組質體來提高綠膿桿菌 PAO1中psrA的表達，並分析其對細菌的影響。轉錄組分析顯示，相較於野生株，大量表現 PsrA顯著下調了群體感應調節因子LasR和RhlR以及許多與群體感應相關的基因表現量。通過使用分別檢測短鏈和長鏈酰基高絲氨酸內酯（N-acyl homoserine lactone）的兩種報告菌株——紫色桿菌（Chromobacterium violaceum）CV026和攜帶[pSB1075]質體的大腸桿菌（Escherichia coli）——評估PAO1 [pMMBpsrA]中自誘導劑（autoinducer）的產生，進一步確認了PsrA在群體感應中的作用。透過同源ΔpsrA、ΔlasR和ΔpsrA-ΔlasR突變株的表型分析表明，PAO1 [pMMBpsrA]中的彈性蛋白酶、酪蛋白酶和游動活性的降低可能是通過LasR介導的。除了群體感應，PsrA還負向調節綠膿桿菌PAO1中的主要脂肪酶LipA，增加其在脂肪酸代謝中的角色層次。電泳遷移率變動分析（electrophoretic mobility shift assays）證明，重組蛋白PsrA可以結合到lasR和lipA的啟動子，這些啟動子中包含的序列與已知的PsrA結合位點具有高相似度。此外，PsrA的效應分子油酸（oleic acid）抑制了PsrA與lasR和lipA啟動子的結合，並恢復了幾種群體感應相關的表現型至野生PAO1的水平。將psrA基因剔除和大量表現psrA的綠膿桿菌PAO1感染蠟蛾（Galleria mellonella）幼蟲揭示了PsrA在綠膿桿菌感染寄主的活體毒性作用。綜合來看，這些發現表明PsrA通過負向調節lasR和lipA的表達來調節群體感應和脂肪酶，且長鏈脂肪酸在此調節過程中的重要信號分子。

The transcription factor PsrA plays a multifaceted role in regulating the type III secretion system, fatty acid metabolism, and the quinolone signaling quorum sensing system in Pseudomonas aeruginosa. This study aimed to further investigate the functions of PsrA by introducing P. aeruginosa PAO1 a recombinant plasmid containing the psrA gene (pMMBpsrA), thereby increasing psrA expression, and analyzing its effects on the bacterium. Transcriptomic analysis showed that PsrA significantly downregulated genes encoding the key quorum-sensing regulators, LasR and RhlR, along with numerous genes associated with quorum sensing. The role of PsrA in quorum sensing was further confirmed by assessing autoinducer production in PAO1 [pMMBpsrA] using two reporter bacterial strains, Chromobacterium violaceum CV026 and Escherichia coli JM109 harboring [pSB1075], which detect short- and long-chain acyl homoserine lactones, respectively. Phenotypic analysis of isogenic ΔpsrA, ΔlasR, and ΔpsrA-ΔlasR mutants indicated that the decreased elastase, caseinase, and swarming activity in PAO1 [pMMBpsrA] were likely mediated through LasR. In addition to quorum-sensing, PsrA negatively regulates the major lipase LipA in P. aeruginosa PAO1, adding another layer to its role in fatty acid metabolism. Electrophoretic mobility shift assays demonstrated that recombinant PsrA could bind to the lasR and lipA promoters, which moderately resembles the previously identified consensus PsrA binding motif. In addition, the PsrA effector molecule oleic acid hampered PsrA binding to the lasR and lipA promoters and restored several quorum-sensing-related phenotypes to wild-type levels. A survival study of Galleria mellonella larvae challenged with deletion and overexpression of psrA of P. aeruginosa PAO1 revealed the toxic effect of PsrA in vivo. Collectively, these observations indicate that psrA coordinates quorum sensing and lipase by negatively regulating lasR and lipA expression, and long-chain fatty acids serve as an important signaling molecule in this regulatory process.

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