Regulation Of Type III Secretion System By Rh1 And PQS Quorum Sensing Systems In Pseudomonas Aeruginosa

Pseudomonas aeruginosa is a major opportunistic pathogen capable of causing a variety of soft tissue infections in susceptible hosts. And it becomes a hot potato on clinical therapy with the increasing of intrinsic resistant to a large number of antibiotics.In Pseudomonas aeruginosa, both Quorum sensing (QS) system and Type III secretion system (T3SS) are important to infection and pathogenicity of the pathogen, so it is necessary to investigate the relationship between QS and T3SS. For this objective, we constructed several QS gene knockout mutants. The promoters of the T3SS genes, exoS , exoY, exoT, exsD-pscA-L were cloned and fused upstream of the luminescence reporter gene cluster, luxCDABE. The reporter constructs were integrated on the chromosome in the wild type strain PA01 and the QS mutants respectively, and the expression of the T3SS genes in these strains was compared. As monitored through luciferase reporter fusion, the expression of exoS and exoT in pqsR mutant were found to increase significantly. At the same time, the Rhl system was found to repress the activities of the four T3SS genes and the Las system had no effect. The results indicate that the Rhl and Pseudomonas Quinolone Signal (PQS) systems play an important role in regulating T3SS gene expression in Pseudomonas aeruginosa.In the previous study of our lab, we constructed a transponson mutagenesis library, several mutants were found to increased the expression of phzA1 in presence of sub-inhibitory tetracycline, including mutant in PA0011, a probable 2-OH-lauroytransferase that control the synthesis of cell envelope and outer membrane. In this study, gene knockout mutant of PA0011 was constructed. The PA0011 mutant exhibits 4-fold increased susceptibilities to tetracycline and other antibiotics. At the same time, expression of PA0011 was found to increase over time in the presence of sub-inhibitory tetracycline and erythromycin concentration. Moreover, in the presence of sub-inhibitory concentration tetracycline, levels of lasI, lasR, rhlI, rhlR, pqsH, pqsR, rhlA, lasB and phzA1 transcripts were elevated several folds respectively in comparison with the wild-type levels. These findings suggest that PA0011 is involved in QS system and susceptibility to antimicrobial agents in P. aeruginosa. PA0011 could play a role as a potential target for antimicrobial agents in P. aeruginosa.