Pseudomonas aeruginosa Las quorum sensing autoinducer suppresses growth and biofilm production in Legionella species

Abstract

Bacteria commonly communicate with each other by a cell-to-cell signalling mechanism known as quorum sensing (QS). Recent studies have shown that the Las QS autoinducer N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C 12 -HSL) of Pseudomonas aeruginosa performs a variety of functions not only in intraspecies communication, but also in interspecies and interkingdom interactions. In this study, we report the effects of Pseudomonas 3-oxo-C 12 -HSL on the growth and suppression of virulence factors in other bacterial species that frequently co-exist with Ps. aeruginosa in nature. It was found that 3-oxo-C 12 -HSL, but not its analogues, suppressed the growth of Legionella pneumophila in a dose-dependent manner. However, 3-oxo-C 12 -HSL did not exhibit a growth-suppressive effect on Serratia marcescens, Proteus mirabilis, Escherichia coli, Alcaligenes faecalis and Stenotrophomonas maltophilia. A concentration of 50 mM 3-oxo-C 12 -HSL completely inhibited the growth of L. pneumophila. Additionally, a significant suppression of biofilm formation was demonstrated in L. pneumophila exposed to 3-oxo-C 12 -HSL. Our results suggest that the Pseudomonas QS autoinducer 3-oxo-C 12 -HSL exerts both bacteriostatic and virulence factor-suppressive activities on L. pneumophila alone. INTRODUCTIONBacteria respond and adapt to a constantly changing environment because they have to compete with other micro-organisms for nutrients. To sense their own environmental conditions, bacteria utilize quorum sensing (QS) systems that operate via small molecules known as autoinducers (Miller & Bassler, 2001). These systems regulate the expression of a number of genes synchronously across the bacterial population. Gram-negative bacteria utilize lipid-based molecules, termed acylhomoserine lactones (AHLs) to communicate with each other, whereas Gram-positive bacteria employ peptide-based molecules, termed autoinducing peptides (Federle & Bassler, 2003;Fuqua & Greenberg, 2002). Autoinducer-2 has been found in a variety of bacteria and is considered to be a universal QS molecule (Xavier & Bassler, 2003). When an autoinducer accumulates to the threshold concentration in a populationdensity manner, the expression triggers induction or repression of certain sets of genes that co-ordinate the behaviour of the bacterial population, including the expression of virulence factors. The mechanisms of QS have been extensively characterized in the pathogenic bacterium Pseudomonas aeruginosa, an important causative agent of nosocomial respiratory and urinary tract infections (Willcox et al., 2008). Ps. aeruginosa produces several virulence factors, including LasB elastase, rhamnolipids, pyocyanin, lipase and hydrogen cyanide that contribute to its pathogenesis (Winstanley & Fothergill, 2009). The las-and rhl-QS systems regulate the production of these virulence factors via N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C 12 -HSL) and N-butanoyl-L-homoserine lactone (C 4 -HSL), respectively. METHODSBacterial strains and culture media. Bacterial strains used ...

Essential Roles and Regulation of the Legionella pneumophila Collagen-Like Adhesin during Biofilm Formation

“…Interestingly, the Pseudomonas aeroginosa homoserine lactone autoinducer (3OC12-HSL) was recently shown to exert a bacteriostatic activity, and decrease biofilm formation of Lp1 . These effects are correlated to the transcriptional down-regulation of lqsR gene in Lp1 [29]. This finding suggests a connection between 3OC12-HSL and the uniquely identified QS system in Lp1 .…”

“…The QS autoinducer 3OC12-HSL of P. aeruginosa which is involved in both intra and inter-species communication has recently been shown to suppress the biofilm production of Lp1 [29]. Thus, to test whether a QS system is involved in the transcriptional regulation of lpg2644 during biofilm formation, the Las QS 3OC12-HSL from P. aeruginosa was used as a model autoinducer.…”

Interspecies Interaction between <i>Pseudomonas aeruginosa</i> and Other Microorganisms

“…Recently, Kimura et al (61) have reported that the 3-oxo-C12-HSL molecule itself also has competitive effects against other bacteria. 3-oxo-C12-HSL specifically suppresses growth and biofilm formation in Legionella pneumophila , although it does not show bacteriocidal or bacteriostatic actions against other Gram-negative bacteria that the authors tested.…”

Roles of Pseudomonas aeruginosa Autoinducers and their Degradation Products, Tetramic acids, in Bacterial Survival and Behavior in Ecological Niches

“…Our previous study demonstrated that 3-oxo-C12-AHL accelerated apoptosis in the neutrophil and monocytic cell lines U-937 and P388D1, but not in the epithelial cell lines CCL-185 and HEp-2 (35). On the other hand, 3-oxo-C12-AHL, but not any of its analogues, was found to suppress growth and biofilm formation in Legionella pneumophila, whereas no bactericidal or bacteriostatic action against other Gram-negative bacteria such as Serratia marcescens, Proteus mirabilis, Escherichia coli, Alcaligenes faecalis and Stenotrophomonas maltophilia was found (17). 3-oxo-C 12 -AHL may also possess some role in interspecies and inter-kingdom communication.…”