Lethality and cooperation of Pseudomonas aeruginosa quorum-sensing mutants in Drosophila melanogaster infection models

Abstract

The virulence profiles of Pseudomonas aeruginosa quorum-sensing (QS) mutants were assessed in Drosophila melanogaster feeding and nicking infection models. Functional RhlIR and LasIR QS systems were required for killing in the fly feeding infection model but were not essential in the fly nicking infection model. Mixed infections between PAO1 and strains harbouring mutations in lasR, rhlI and lasI rhlI resulted in increased lethality in the fly feeding model compared with either isolate alone. These results suggested that the parental strain could cooperate with QS mutants in the Drosophila feeding infection model. Finally, the mixed infection between PAO1 and an rhlR mutant resulted in spiteful behaviour and reduced pathogenicity of the mixed culture. INTRODUCTIONQuorum sensing (QS) regulates the cell density-dependent expression of target genes that modulate many bacterial phenotypes, and allows bacteria to behave as multicellular organisms, reaping benefits unattainable by individual bacteria. The most common QS systems in Gram-negative bacteria are composed of transcriptional regulators encoded by luxR homologues and autoinducer biosynthetic enzymes encoded by luxI homologues (de Kievit & Iglewski, 2000;Salmond et al., 1995). Pseudomonas aeruginosa contains two such QS systems, the lasIR and rhlIR regulatory systems (Pearson et al., 1995). These systems are interdependent, interact with the Pseudomonas quinolone signal (PQS), and control a wide range of genes including those for virulence factors, sigma factors and other regulators (Albus et al., 1997;Brint & Ohman, 1995;Erickson et al., 2004;McKnight et al., 2000;Ochsner et al., 1995;Toder et al., 1991;Whiteley et al.,1999). The LasIR system consists of LasI, which synthesizes N-(3-oxo-dodecanoyl)-L-homoserine lactone (3-oxo-C 12 -HSL), and the transcriptional regulator LasR (Pearson et al., 1994). The RhlIR system consists of the transcriptional regulator RhlR and the cognate homoserine lactone synthase RhlI, which synthesizes N-butanoyl-L-homoserine lactone (C 4 -HSL) (Winson et al., 1995).QS is known to be required for P. aeruginosa virulence in many organisms that serve as infection models, suggesting that this is an integral component of bacterial pathogenesis (Lesprit et al., 2003;Pearson et al., 2000;Rumbaugh et al., 1999b; Stoltz et al., 2008;Wu et al., 2001;Zhu et al., 2004). Detection of QS system gene targets and their cognate signalling molecules suggests that these systems are active during human infection, e.g. the chronic lung infections associated with cystic fibrosis (CF) (Erickson et al., 2002). However, the role that QS plays in chronic human infections is unclear, as mutants in QS genes frequently occur in clinical isolates (Schaber et al., 2004;Smith et al., 2006). In particular, lasR mutants frequently arise in CF infections (Smith et al., 2006), and in some model infections can be maintained alongside the parental strains (D'Argenio et al., 2007; Kohler et al., 2010;Smith et al., 2006). It has been speculated that QS systems can have a...

Promise for plant pest control: root-associated pseudomonads with insecticidal activities

“…In the nicking model rapid killing within 1–2 days after pricking flies with a needle dipped into a bacterial culture is observed, whereas the feeding model allows to monitor an extended infection process of 1–2 weeks after ingestion of a high concentration of bacteria by the flies. Using these models, considerable strain variation in virulence of P. aeruginosa to Drosophila was observed (Lutter et al, 2012) coinciding with similar observations for P. fluorescens group bacteria (Olcott et al, 2010). The variations in the pathogenicity are likely to mirror differences in the genomic equipage with relevant virulence genes and in the regulation of these genes in the different strains.…”

Development of an Ex Vivo Porcine Lung Model for Studying Growth, Virulence, and Signaling of Pseudomonas aeruginosa

“…aeruginosa to establish acute infections (31–36). We also found that in ASM in the absence of pig lung, lasR mutants were less fit than the WT.…”

“…We focused on the well-characterized PAO1 wild-type (WT) strain and two lasR mutant strains which do not respond to the QS signal N -(3-oxododecanoyl)- l -homoserine lactone (3-oxo-C 12 -HSL) (49). QS controls the expression of various exoproducts (49) and facilitates the establishment of acute infection (31–36). However, mutants that have lost LasR function and so do not respond to 3-oxo-C 12 -HSL commonly arise in chronic CF infections (9, 10, 12) and ventilator-associated pneumonia (50).…”

Small flies to tackle big questions: assaying complex bacterial virulence mechanisms usingDrosophila melanogaster

“…Finally, various commensal flora in different laboratories may also impact the severity of the outcome of the infection (see also below). Screens of P. aeruginosa mutants, in either injured or orally infected flies, have highlighted the involvement of twitching motility factors Potvin et al, 2003), QS regulators , and a number of either previously known or newly discovered QS regulated genes, in full virulence towards Drosophila (Chugani et al, 2001;Lau et al, 2003;Erickson et al, 2004;Kim et al, 2008;Lutter et al, 2012). Moreover, we showed the importance of T3SS for full virulence of the cystic fibrosis isolate CHA and identified new regulators of QS or T3SS, which are commonly required for full virulence of PAO1 in amoebae, mice and orally infected flies (Fauvarque et al, 2002;Alibaud et al, 2008).…”