Bertani Iris, Rampioni Giordano, Leoni Livia, Venturi Vittorio
International Centre for Genetic Engineering and Biotechnology, Padriciano, Trieste, Italy.
BMC Microbiol. 2007 Jul 26;7:71. doi: 10.1186/1471-2180-7-71.
In Pseudomonas putida and Pseduomonas aeruginosa, the similar PpuR/RsaL/PpuI and LasR/RsaL/LasI acyl homoserine lactones (AHLs) quorum sensing (QS) systems have been shown to be under considerable regulation by other global regulators. A major regulator is the RsaL protein which strongly directly represses the transcription of the P. putida ppuI and P. aeruginosa lasI AHL synthases. In this study we screened a transposon mutant bank of P. putida in order to identify if any other regulators were involved in negative regulation of AHL QS.
In our screen we identified three Tn5 mutants which displayed overproduction of AHLs in P. putida strain WCS358. Two of the mutants had a Tn5 located in the rsaL gene, whereas in one mutant the transposon was located in the lon protease gene. Lon proteases play important roles in protein quality control via degradation of misfolded proteins. It was determined that in the P. putida lon mutant, AHL levels, PpuR levels and ppuI promoter activity all increased significantly; we therefore postulated that PpuR is a target for Lon. The Lon protease had no effect on AHL production in P. aeruginosa.
The Lon protease is a negative regulator of AHL production in P. putida WCS358. The Lon protease has also been shown by others to influence AHL QS in Vibrio fischeri and Agrobacterium tumefaciens and can thus become an important regulator of AHL QS timing and regulation in bacteria.
在恶臭假单胞菌和铜绿假单胞菌中,相似的PpuR/RsaL/PpuI和LasR/RsaL/LasI酰基高丝氨酸内酯(AHLs)群体感应(QS)系统已被证明受到其他全局调控因子的显著调控。一个主要的调控因子是RsaL蛋白,它强烈直接抑制恶臭假单胞菌ppuI和铜绿假单胞菌lasI AHL合成酶的转录。在本研究中,我们筛选了恶臭假单胞菌的转座子突变文库,以确定是否有其他调控因子参与AHL QS的负调控。
在我们的筛选中,我们鉴定出三个Tn5突变体,它们在恶臭假单胞菌WCS358菌株中表现出AHLs的过量产生。其中两个突变体的Tn5位于rsaL基因中,而在一个突变体中,转座子位于lon蛋白酶基因中。Lon蛋白酶通过降解错误折叠的蛋白质在蛋白质质量控制中发挥重要作用。已确定在恶臭假单胞菌lon突变体中,AHL水平、PpuR水平和ppuI启动子活性均显著增加;因此我们推测PpuR是Lon的作用靶点。Lon蛋白酶对铜绿假单胞菌的AHL产生没有影响。
Lon蛋白酶是恶臭假单胞菌WCS358中AHL产生的负调控因子。其他人也已证明Lon蛋白酶会影响费氏弧菌和根癌土壤杆菌中的AHL QS,因此它可能成为细菌中AHL QS时间调控和调节的重要调控因子。