Alginate Oligosaccharide-Induced Modification of the lasI-lasR and rhlI-rhlR Quorum Sensing Systems in Pseudomonas aeruginosa.

Pseudomonas aeruginosa plays a major role in many chronic infections. Its ability to readily form biofilms contributes to its success as an opportunistic pathogen and its resistance/tolerance to antimicrobial/antibiotic therapy. A low molecular weight alginate oligomer (OligoG CF-5/20), derived from marine algae, has previously been shown to impair motility in P. aeruginosa biofilms and disrupt pseudomonal biofilm assembly. As these bacterial phenotypes are regulated by quorum sensing (QS), we hypothesized that OligoG CF-5/20 may induce alterations in QS signalling in P. aeruginosa QS regulation was studied using Chromobacterium violaceum CV026 biosensor assays that showed a significant reduction in acyl homoserine lactone (AHL) production following OligoG CF-5/20 treatment (≥2%; P<0.05). This effect was confirmed by liquid chromatography/mass spectrometry (LC/MS) analysis of C4-AHL and 3-oxo-C12-AHL production (≥2%; P<0.05). Moreover, quantitative PCR (qPCR) showed that reduced expression of both the las and rhl systems was induced following 24 h treatment with OligoG CF-5/20 (≥0.2%; P<0.05). Circular dichroism (CD) spectroscopy indicated that these alterations were not due to steric interaction between the AHL and OligoG CF-5/20. Confocal laser scanning microscopy and COMSTAT image analysis demonstrated that OligoG CF-5/20 treated biofilms had a dose-dependent decrease in biomass which was associated with inhibition of eDNA synthesis (≥0.5%; P<0.05). These changes correlated with alterations in extracellular production of the pseudomonal virulence factors pyocyanin, rhamnolipids, elastase and total protease (P<0.05). The ability of OligoG CF-5/20 to modify QS signalling in P. aeruginosa PAO1 which may influence critical downstream functions, such as virulence factor production and biofilm formation.