Quinolone signaling in the cell-to-cell communication system of Pseudomonas aeruginosa

Numerous species of bacteria use an elegant regulatory mechanism known as quorum sensing to control the expression of specific genes in a cell-density dependent manner. In Gram-negative bacteria, quorum sensing systems function through a cell-to-cell signal molecule (autoinducer) that consists of a homoserine lactone with a fatty acid side chain. Such is the case in the opportunistic human pathogen Pseudomonas aeruginosa, which contains two quorum sensing systems (las and rhl) that operate via the autoinducers, N-(3-oxododecanoyl)-L-homoserine lactone and N-butyryl-Lhomoserine lactone. The study of these signal molecules has shown that they bind to and activate transcriptional activator proteins that specifically induce numerous P. aeruginosa virulence genes. We report here that P. aeruginosa produces another signal molecule, 2-heptyl-3-hydroxy-4-quinolone, which has been designated as the Pseudomonas quinolone signal. It was found that this unique cell-to-cell signal controlled the expression of lasB, which encodes for the major virulence factor, LasB elastase. We also show that the synthesis and bioactivity of Pseudomonas quinolone signal were mediated by the P. aeruginosa las and rhl quorum sensing systems, respectively. The demonstration that 2-heptyl-3- hydroxy-4-quinolone can function as an intercellular signal sheds light on the role of secondary metabolites and shows that P. aeruginosa cell-to-cell signaling is not restricted to acyl-homoserine lactones. Originally published Proc. Natl. Acad. Sci, Vol. 96, No. 20, Sep. 199

Contribution of the Pseudomonas aeruginosa class II and class III ribonucleotide reductases to anaerobic growth and biofilms

Thesis (Ph. D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Microbiology and Immunology, 2008.P. aeruginosa is an opportunistic pathogen that is the primary cause of morbidity and mortality in individuals with cystic fibrosis (Cf) due to pulmonary failure. Numerous virulence factors, an inherent resistance to antibiotics, and the ability to form biofilms all contribute to the difficulty in eradicating these bacteria. There is growing evidence for the development of anaerobic niches in biofilms as well as P. aeruginosa growing in the natural environment. P. aeruginosa can grow in the absence of oxygen by denitrification if provided with a suitable electron acceptor or by arginine catabolism. However, very little is known regarding the physiology of anaerobically grown P. aeruginosa. A class II ribonucleotide reductase (RNR), later named nrdJab, was found in a random transposon mutagenesis in an effort to identify genes or gene products required for anaerobic growth of P. aeruginosa. This indicated that P. aeruginosa uses the class II RNR for anaerobic growth. After anaerobic adaptation, growth of a ΔnrdJab mutant was comparable to wild-type PAO1. A nucleotide sequence analysis of the P. aeruginosa genome also indicated the presence of a putative class III (NrdDG) RNR. After anaerobic adaptation, growth of a ΔnrdDG mutant was also comparable to wild-type PAO1. A mutant lacking both nrdJab and nrdDG was unable to grow at all anaerobically, suggesting that P. aeruginosa requires at least one RNR for anaerobic growth. A previous microarray analysis reported that nrdJab expression is increased under anaerobic conditions as compared to aerobic conditions. A lacZ-transcriptional fusion of nrdJab was used to confirm this finding. The expression of a lacZ-transcriptional fusion of nrdDG is also higher under anaerobic conditions as compared to aerobic conditions. vi Both of the nrdJab and nrdDG RNRs are regulated by Anr, a P. aeruginosa anaerobic regulator. We hypothesized that the growth of the RNR mutants might be adversely affected in biofilms, as anaerobic niches develop in biofilms. Biofilms of mutants lacking both nrdJab and nrdDG were significantly reduced in viability after 120 hours. nrdJab and nrdDG were expressed in a 120-hour biofilm. This evidence suggests that NrdJab and NrdDG are important for anaerobic growth of the cells within a biofilm as well as serving as genetic indicators for anaerobiosis. To determine if nrdJa and nrdD are genetically conserved PCR was performed using P. aeruginosa clinical isolates. All of the isolates tested harbored nrdJa and nrdD. The high conservation of nrdJa and nrdD in addition to the studies revealed in this thesis suggest that the P. aeruginosa NrdJab and NrdDG RNRs may serve as potential targets for future antimicrobial therapy

Azithromycin Retards Pseudomonas aeruginosa Biofilm Formation

Using a flow cell biofilm model, we showed that a sub-MIC of azithromycin (AZM) can delay but not inhibit Pseudomonas aeruginosa biofilm formation and results in the development of a stable AZM resistance phenotype. Furthermore, mature biofilms were not affected by AZM

Cell-to-Cell Signaling and Pseudomonas aeruginosa Infections

Pseudomonas aeruginosa is a bacterium responsible for severe nosocomial infections, life-threatening infections in immunocompromised persons, and chronic infections in cystic fibrosis patients. The bacterium's virulence depends on a large number of cell-associated and extracellular factors. Cell-to-cell signaling systems control the expression and allow a coordinated, cell-density–dependent production of many extracellular virulence factors. We discuss the possible role of cell-to-cell signaling in the pathogenesis of P. aeruginosa infections and present a rationale for targeting cell-to-cell signaling systems in the development of new therapeutic approaches