Abstract
Pseudomonas aeruginosa (P. aeruginosa) modulates the expression of a myriad of virulence factors via two complicated hierarchical quorum-sensing (QS) cascade. This study shed light on the interrelation between P. aeruginosa QS systems and pyocyanin production. Transcription analysis of lasR, rhlR, rhlI and phz genes using quantitative real time-reverse transcriptase PCR (qRT-PCR) assay, followed by sequencing of the autoinducer synthase (lasI gene) were applied for 15 P. aeruginosa strains recovered from diverse animal clinical sources. Expression studies revealed that most P. aeruginosa strains demonstrated statistically significant differences (p < 0.05) with a very wide range of transcript levels of QS and phz genes in comparison to P. aeruginosa ATCC 27853. We have identified significant positive correlations (r ≥ 0.3) between the expressions of QS and phz genes in eleven analyzed strains, whereas pyocyanin production positively correlated with the expression of lasR only in three strains (r ≥ 0.6). We further found that there was a negative correlation between the transcript levels of QS and phz genes in one bacterial strain. Analysis of lasI sequences showed point mutations explaining the alterations in pyocyanin expression. The deficiencies of lasI, lasR and rhlI with rhlR-dependent expression of phz in one strain were also recorded. These results provided new insights to the pivotal role of QS signal molecules on pyocyanin production presenting the las system as the dominant regulator.
Highlights
Pseudomonas aeruginosa (P. aeruginosa) modulates the expression of a myriad of virulence factors via two complicated hierarchical quorum-sensing (QS) cascade
Since P. aeruginosa strains were selected for their range of pigment activities, different levels of pigmentation on isolation media were observed due to varying amounts of pyocyanin produced
Our results provide additional evidence supporting this hypothesis; an extensive analysis of transcriptional responses using qRT-PCR indicated that most P. aeruginosa strains showed significantly higher expression levels of QS systems and their regulated genes in comparison to the reference strain, while they were parallel to that produced by the wild type in a previous study [14]
Summary
Pseudomonas aeruginosa (P. aeruginosa) modulates the expression of a myriad of virulence factors via two complicated hierarchical quorum-sensing (QS) cascade. Methodology: Transcription analysis of lasR, rhlR, rhlI and phz genes using quantitative real time-reverse transcriptase PCR (qRT–PCR) assay, followed by sequencing of the autoinducer synthase (lasI gene) were applied for 15 P. aeruginosa strains recovered from diverse animal clinical sources. Results: Expression studies revealed that most P. aeruginosa strains demonstrated statistically significant differences (p < 0.05) with a very wide range of transcript levels of QS and phz genes in comparison to P. aeruginosa ATCC 27853. The deficiencies of lasI, lasR and rhlI with rhlR-dependent expression of phz in one strain were recorded. Each signaling QS system is comprised of two components, the autoinducer synthases (lasI and rhlI) and their cognate transcriptional regulators (lasR and rhlR), respectively [3]. The two systems are intimately connected being hierarchically organized with lasI/R system regulating rhlI-rhlR transcription [5]. Pyocyanin is the major soluble bluish green phenazine derivative that is unique for P. aeruginosa suppurative infections [6]
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