Colonies were grown for 3 days at 37°C. Hydrated lasR mutant biofilms do not show altered architecture The involvement of pel in the wrinkled colony morphology of the ZK lasR mutant suggested that it might exhibit generally altered
biofilm architecture. We investigated pellicle formation of standing cultures as well as biofilm formation in microtiter plates and flow-cells. Flow-cell biofilms of the wild-type and the lasR mutant after 3 days of growth are shown in Figure 5. Neither assay revealed any differences between the two strains. This is consistent with recent results by Colvin et al., who also found no defect in attachment or biofilm development for a pel mutant of strain PAO1 . There is a difference in the degree of buy EPZ-6438 hydration in the three biofilm assays we employed. Submerged flow-cell biofilms are fully saturated and hydrated, pellicles and microtiter plate biofilms that form at the air-liquid interface are somewhat
less hydrated, whereas colonies on agar Tamoxifen price are the least hydrated . It is possible that the observed phenotype only manifests under conditions of low hydration. Figure 5 Flow-cell biofilms. CLSM images of flow-cell grown biofilms of the ZK wild-type (WT) and the lasR mutant at 37°C after 3 days. The large panel shows the horizontal cross-section and the small panel shows the vertical cross-section of the biofilm. The lines in the panels indicate the planes of the cross-sections. Suppressor mutagenesis implicates the pqs pathway Transposon mutagenesis was performed in the ZK lasR mutant background to identify the regulatory link between the las QS system and colony morphology. Around 10,000 mutants were screened for reversion to a smooth phenotype. We identified 38 mutants, and mapped very transposon insertions in 25 (Additional file 2: Table S2). We found 9 transposon insertions in the pqsA-D genes of the AQ biosynthesis operon and one insertion in the gene encoding the transcriptional regulator PqsR that activates pqsA-E expression (Figure 6). Given the large fraction of hits (10 out of 25 or 40%), the role of the pqs operon was apparent even without mapping
the remaining transposon mutants. We did not identify any insertions in pqsH, which promotes the conversion of Series A (4-hydroxyalkyl quinolines) to Series B (3,4 dihydroxyalkyl quinolines) congeners nor in pqsE, which encodes a putative global regulator [20, 58]. Surprisingly, we also did not identify a transposon insertion in the pel operon, although our data in Figure 3 show that the lasR pel mutant forms a smooth colony. We found that this mutant displayed very slight wrinkling under the conditions employed for the high throughput screen, in which our primary focus was on the identification of the most obvious smooth revertants. Figure 6 The pqs locus and transposon insertions in associated suppressor mutants. Horizontal arrows represent the genes of the pqsA-E operon, the pqsR transcriptional regulatory gene, and the pqsH gene.