Pseudomonas aeruginosa is a Gram-negative rod-shaped bacterium renowned for its environmental and metabolic versatility. It is a common inhabitant of soil and water and can also be isolated from plants and animals. P. aeruginosa is an opportunistic pathogen associated with immunocompromised hosts. It can cause fatal infections in individuals suffering from cystic fibrosis, severe burn wounds or neutropenia. This bacterium is also noted for its resistance to many antibiotics.

We have identified a large number of novel virulence-related genes and demonstrated that have greatly reduced pathogenicity in several infection models, yet sustain wild-type viability. The genes identified encode proteins involved in transcriptional and post-translational control, efflux systems, biosynthetic enzymes, virulence effectors as well as proteins of unknown function. We are currently studying a number of these factors.

A principal project in the Rahme laboratory seeks to characterize P. aeruginosa genes that encode wide-host range virulence factors, and to determine how these factors mediate infection. One of the virulence factors identified is the LysR-type transcriptional regulator MvfR (multiple virulence factor regulator). MvfR, which we first identified in plant hosts, controls the 4-hydroxy-2-alkylquinolines (HAQs) quorum sensing (QS) system. MvfR regulon studies (1, 2, 3, 4-6, 7, 8) have revealed an unprecedented P. aeruginosa virulence mechanism (see below), and identified a new indispensable player in P. aeruginosa’s cell density-dependent quorum-sensing (QS) virulence network. We have demonstrated MvfR’s key role in the control of multiple QS-regulated virulence factors that mediate burn wound and lung infections, and showed that MvfR controls the synthesis of a large family of HAQs, including 4-hydroxy-2-heptylquinoline (HHQ), and 3,4-dihydroxy-2-heptylquinoline (PQS). PQS and HHQ are required for MvfR activation, and HHQ is the major MvfR co-ligand in vivo (7). MvfR controls HAQ synthesis by binding and positively regulating expression of the HAQ biosynthetic operons pqsA-D (7) and phnAB (5). That MvfR can intercept opioid compounds released during host stress and integrate them into core elements of quorum sensing circuitry leading to enhanced virulence (12), further corroborates the importance of the MvfR/HAQ pathway in human infections cause by P. aeruginosa. We have identified a series of compounds that interfere with MvfR regulon activation and/or HAQ synthesis (please see anti-infectives page). These compounds limit P. aeruginosa infections and virulence with high efficacy in mice, and thus are potential therapeutics against human-P. aeruginosa pathogenicity.

The Rahme laboratory is also studying the biological role and activity of many of the HAQs molecules whose synthesis is controlled by MvfR. The biosynthetic operons pqsABCDE and phnAB encode enzymes that catalyze the biosynthesis of 54 distinct HAQs, including HHQ and PQS. While HHQ and PQS directly bind to and activate the MvfR regulatory protein, and serve as its in vivo activation ligands, the biological function of all other HAQs remains elusive.

MvfR and HAQ selected publications:

1. Cao, H., G. Krishnan, B. Goumnerov, J. Tsongalis, R. Tompkins, and L. G. Rahme. 2001. A quorum sensing-associated virulence gene of Pseudomonas aeruginosa encodes a LysR-like transcription regulator with a unique self-regulatory mechanism. Proc Natl Acad Sci U S A 98:14613-8.

2. Déziel, E., S. Gopalan, A. P. Tampakaki, F. Lepine, K. E. Padfield, M. Saucier, G. Xiao, and L. G. Rahme. 2005. The contribution of MvfR to Pseudomonas aeruginosa pathogenesis and quorum sensing circuitry regulation: multiple quorum sensing-regulated genes are modulated without affecting lasRI, rhlRI or the production of N-acyl-L-homoserine lactones. Mol Microbiol 55:998-1014.

3. Déziel, E., F. Lépine, S. Milot, J. He, M. N. Mindrinos, R. G. Tompkins, and L. G. Rahme. 2004. Analysis of Pseudomonas aeruginosa 4-hydroxy-2- alkylquinolines (HAQs) reveals a role for 4-hydroxy-2- heptylquinoline in cell-to-cell communication. Proc Natl Acad Sci U S A.

4. Lepine, F., E. Deziel, S. Milot, and L. G. Rahme. 2003. A stable isotope dilution assay for the quantification of the Pseudomonas quinolone signal in Pseudomonas aeruginosa cultures. Biochim Biophys Acta 1622:36-41.

5. Lepine, F., S. Milot, E. Deziel, J. He, and L. G. Rahme. 2004. Electrospray/mass spectrometric identification and analysis of 4-hydroxy-2-alkylquinolines (HAQs) produced by Pseudomonas aeruginosa. J Am Soc Mass Spectrom 15:862-9.

6. Lesic B., F. Lépine, E. Déziel, J. Zhang, Q. Zhang, K. Padfield, M-H. Castonguay, S. Milot, S. Stachel, AA. Tzika, RG. Tompkins, and L.G. Rahme. 2007. Inhibitors of bacterial pathogen intercellular signals as selective anti-infective compounds. PLoS Pathog. 2007 Sep 14;3(9):1229-39.7.

7. Xiao, G., E. Deziel, J. He, F. Lepine, B. Lesic, M. H. Castonguay, S. Milot, A. P. Tampakaki, S. E. Stachel, and L. G. Rahme. 2006. MvfR, a key Pseudomonas aeruginosa pathogenicity LTTR-class regulatory protein, has dual ligands. Mol Microbiol.

8. Xiao, G., J. He, and L. G. Rahme. 2006. Mutation analysis of the Pseudomonas aeruginosa mvfR and pqsABCDE gene promoters demonstrates complex quorum-sensing circuitry. Microbiology 152:1679-86.

9. Mahajan-Miklos, S., M. W. Tan, L. G. Rahme, and F. M. Ausubel. 1999. Molecular mechanisms of bacterial virulence elucidated using a Pseudomonas aeruginosa-Caenorhabditis elegans pathogenesis model. Cell 96:47-56.

10. Rahme, L. G., F. M. Ausubel, H. Cao, E. Drenkard, B. C. Goumnerov, G. W. Lau, S. Mahajan-Miklos, J. Plotnikova, M.-W. Tan, T. J., C. Walendziewicz, and R. G. Tompkins. 2000. Plants and Animals Share Functionally Common Bacterial Virulence Factors. Proc. Natl. Acad. Sci. USA 97:8815-8821.

11. Rahme, L. G., M.-W. Tan, L. Le, S. M. Wong, R. G. Tompkins, S. B. Calderwood, and F. M. Ausubel. 1997. Use of model plants hosts to identify Pseudomonas aeruginosa virulence factors. Proc. Natl. Acad. Sci. USA 94:13245-13250.

12. Zaborina, O., F. Lepine, G. Xiao, V. Valuckaite, Y. Chen, T. Li, M. Ciancio, A. Zaborin, E. Petroff, J. R. Turner, L. G. Rahme, E. Chang, and J. C. Alverdy. 2007. Dynorphin Activates Quorum Sensing Quinolone Signaling in Pseudomonas aeruginosa. PLoS Pathog 3:e35.