Differential Modulation of Quorum Sensing Signaling through QslA in Pseudomonas aeruginosa Strains PAO1 and PA14

Abstract

Two clinical isolates of the opportunist pathogen Pseudomonas aeruginosa named PAO1 and PA14 are commonly studied in research laboratories. Despite the isolates being closely related, PA14 exhibits increased virulence compared to that of PAO1 in various models. To determine which players are responsible for the hypervirulence phenotype of the PA14 strain, we elected a transcriptomic approach through RNA sequencing. We found 2,029 genes that are differentially expressed between the two strains, including several genes that are involved with or regulated by quorum sensing (QS), known to control most of the virulence factors in P. aeruginosa. Among them, we chose to focus our study on QslA, an antiactivator of QS whose expression was barely detectable in the PA14 strain according our data. We hypothesized that lack of expression of qslA in PA14 could be responsible for higher QS expression in the PA14 strain, possibly explaining its hypervirulence phenotype. After confirming that QslA protein was highly produced in PAO1 but not in the PA14 strain, we obtained evidence showing that a PAO1 deletion strain of qslA has faster QS gene expression kinetics than PA14. Moreover, known virulence factors activated by QS, such as (i) pyocyanin production, (ii) H2-T6SS (type VI secretion system) gene expression, and (iii) Xcp-T2SS (type II secretion system) machinery production and secretion, were all lower in PAO1 than in PA14, due to higher qslA expression. However, biofilm formation and cytotoxicity toward macrophages, although increased in PA14 compared to PAO1, were independent of QslA control. Together, our findings implicated differential qslA expression as a major determinant of virulence factor expression in P. aeruginosa strains PAO1 and PA14. IMPORTANCE Pseudomonas aeruginosa is an opportunistic pathogen responsible for acute nosocomial infections and chronic pulmonary infections. P. aeruginosa strain PA14 is known to be hypervirulent in different hosts. Despite several studies in the field, the underlining molecular mechanisms sustaining this phenotype remain enigmatic. Here we provide evidence that the PA14 strain has faster quorum sensing (QS) kinetics than the PAO1 strain, due to the lack of QslA expression, an antiactivator of QS. QS is a major regulator of virulence factors in P. aeruginosa; therefore, we propose that the hypervirulent phenotype of the PA14 strain is, at least partially, due to the lack of QslA expression. This mechanism could be of great importance, as it could be conserved among other P. aeruginosa isolates.

Improving sustainability in wood coating: testing lignin and cellulose nanocrystals as additives to commercial acrylic wood coatings for bio-building

“…The blue-green colour in Fig. 3c derives from the bacterial redox state, because P. aeruginosa produces pigments as secondary metabolites (i.e., pyocyanin, fluorescein, pyorubrin and pyomelanin) when reaching a stationary growth phase, often related to quorum sensing (QS) responses and modulation of pyocyanin as virulence factor (Sana et al 2019). This response was more visible around the sample spots where the formulation contains lignin (sample 3 in Fig.…”

“…This could explain the limited efficacy of lignin in inhibiting PA02-1 growth. Surprisingly, the PA02-1 isolate can exploit lignin for accelerating the external production of QS factors (pyocyanin), often involved in the virulence and adaptive response to environment of P. aeruginosa (Sana et al 2019). However, this effect might appear higher in W-LN formulations and less evident in the Av-LN ones, and this might suggest, at least for this strain, that Av is able to produce delaying effects in QS responses, specifically related in the production of phenazines.…”

Pseudomonas aeruginosa reference strains PAO1 and PA14: A genomic, phenotypic, and therapeutic review

“…High levels of QslA protein were produced in the lower virulence PAO1 strain, whereas the QslA protein was minimally expressed in the hypervirulent PA14 strain. Deleting the qslA gene from PAO1 resulted in QS gene expression rates that were higher than those of PA14 ( Sana et al, 2019 ). Notably, PAO1 and PA14 strains were grown in the traditional lysogeny broth (LB) media.…”

“…There are key differences between PA14 and PAO1 quorum sensing (QS) mechanisms, which, in part, regulate the expression of virulence genes in a bacterial cell density-dependent manner ( Lee and Zhang, 2015 ; Sana et al, 2019 ). Generally, QS in P. aerguinosa is governed by three systems—Las, Rhl, and Pqs that have been elegantly reviewed ( Chadha et al, 2022 ).…”

Compendium-wide analysis of P. aeruginosa core and accessory genes reveal more nuanced transcriptional patterns

“…For example, a study by Sana et al found a set of core genes that were differentially expressed in PAO1 compared to PA14. 32 Many of these genes were involved in quorum sensing, which is a cell-cell signaling communication system that regulates many virulence factors. 33 For another example, within the type III secretion system (T3SS), which is a virulence determinant that allows P. aeruginosa to deliver toxic effector proteins to host cells.…”