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

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 OS 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 mu M 3-oxo-C-12-HSL completely inhibited the growth of L. prieurriophila. 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.