PqsA-D enzymes are involved in the synthesis of 4-hydroxyalkyl quinolines (named Series A congeners
by Deziel et al.) [20]. This class of compounds is converted to 3, 4 dihydroxyquinolines (Series B congeners) by a monoxygenase encoded by the pqsH gene [20]. The most prominent Series A congeners are 4-hydroxy-2-heptyl quinoline (HHQ) and 4-hydroxy-2-nonyl quinoline (HNQ), and the most prominent Series B congener is 3,4-dihydroxy-2-heptyl quinoline (PQS), due to their established roles as cell-cell signaling molecules. HHQ/HNQ and PQS bind PqsR with low and high affinity, respectively, and are capable of activating the protein [21–23]. LasR positively regulates AQ production by upregulating pqsR [22]
and pqsH [20, 24] transcription, although under certain culture conditions, MK 8931 nmr AQ can also be produced in the absence of a functional las system [25]. The rhl system, in turn, represses pqsR and pqsA-E expression [22, 26, 27]. The AQ biosynthetic enzymes enable P. aeruginosa to produce more than 50 MEK inhibitor distinct AQ molecules [20, 28]. Together, the three QS systems, las, rhl, and pqs, regulate > 5% of the P. aeruginosa genome [29–32]. Several studies have investigated the LY3009104 mw contribution of each QS system to biofilm formation. A functional las system is required for formation of highly structured SSA biofilm communities in P. aeruginosa PAO1 Reverse transcriptase [33]. The las system influences biofilm matrix formation and activation of pel EPS [6]. In another study, the las system was shown to indirectly inhibit
pel expression through weak activation of the tyrosine phosphatase TpbA [34]. The rhl QS system contributes to maintenance of biofilm architecture through production of rhamnolipid surfactants [35]. The pqs system in turn is implicated in autolysis [36] and maintaining biofilm integrity as a consequence of eDNA release [37]. In addition, the contribution of QS to biofilm formation is modulated by environmental factors such as nutritional cues [38]. Taken together, the role of QS in biofilm formation is multifactorial. Our recent work suggested yet another connection between QS and EPS production. We showed by chromatin immunoprecipitation-microarray analysis (CHIP-chip) and electrophoretic mobility shift assay that LasR binds to the putative promoter region of the Psl EPS operon [8] (Figure 1). This finding led us to investigate in more detail how lasR mutation affects EPS production and colony biofilm formation. A lasR mutant of P. aeruginosa strain ZK2870 exhibited a pronounced wrinkled colony morphology at 37°C suggesting a possible link between las QS and psl expression. However, we found that the wrinkled phenotype is pel rather than psl-dependent. Subsequent suppressor mutagenesis in the lasR mutant background implicated the involvement of the pqs pathway.