Quorum Sensing in Vibrio fischeri

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1 Quorum Sensing in Vibrio fischeri Quorum Sensing (QS) is a type of bacterial cell-to-cell communication, which enables a single cell to sense the number (concentration) of bacteria within a population. QS is achieved through the production, release and detection of special signaling molecules called autoinducers. Each cell produces autoinducer molecules and releases them into the environment. By continuously monitoring the concentration of these molecules in the environment each cell can sense the number of bacteria in the population. Many bacterial systems with QS behavior have been discovered and studied. The marine bioluminescent bacteria Vibrio fischeri is one such interesting and well-studied system. The V.fischeri bacterium exists in a free-living state or as a symbiont of certain luminescent fish or squid. The bacteria luminesce only when present in large concentrations and do not emit light when in the free-living state. Research into the regulatory mechanism of bioluminescence in these bacteria led to the discovery of QS behavior in the system. The luminescence genes turn on only when the cell density is high. QS in V.fischeri relies on the synthesis, release and subsequent sensing of a signal molecule (autoinducer) known as N-acyl homserine lactone (AHL). AHL is synthesized by the protein LuxI and sensed by the protein LuxR. When cell density is low, concentration of AHL in the surrounding area is low. As cell density increases, concentration of AHL increases. When the AHL in the environment reaches a specific threshold concentration, it interacts with the LuxR protein to form a complex. The LuxR-AHL complex then causes the luminescence genes to be switched on. This complex also causes AHL to be produced in large quantities than before. Thus, the AHL is able to autoinduce its own synthesis. There is a vast amount of experimental literature available about this system. Efforts to model the QS behavior in this system are mostly based on differential equations. Few authors have also adopted a hybrid modeling approach. This is a very interesting system to study and I will delve into the details of the existing modeling approaches and key biological findings over the next week. Given below is a list of references which seemed relevant at first glance. Bibliography: 1. Belta, C., Schug, J., Dang, T., Kumar, V., Pappas, G. J., Rubin, H. and Dunlap, P. V. (2001) Stability and reachability analysis of a hybrid model of luminescence in the marine bacterium V.fischeri. Grasp lab, University of Pennsylvania, Philadelphia, PA. 2. Brookfield, J. F. Y. (1998) Quorum Sensing and Group Selection. Evolution. 52,

2 3. Brown, S. P. and Johnstone, R. A. (2001) Cooperation in the dark: signalling and collective action in quorum-sensing bacteria. Proc. R. Soc. Lond. B, 268, Callahan, S. M., Dunlap, P. V. (2000) LuxR and acyl-homoserine-lactonecontrolled non-lux genes define a quorum-sensing regulon in Vibrio fischeri. J. Bacteriol., 182, Davies, D. G., Parsek, M. R., Pearson, J. P. Iglewski, B. H. Costerton, J. W. and Greenberg, E. P. (1998) The involvement of cell-to-cell signals in the development of a bacterial biofilm. Science Dockery, J.D. and Keener, J.P. (2001) A mathematical model for quorum sensing in Pseudomonas aeruginosa. Bull. Math. Biol., 63, Dunlap, P. V. and Kuo, A. (1992) Cell density-dependent modulation pf the Vibrio fischeri luminescence system in the absence of autoinducer and LuxR protein. J. Bacteriol. 174(8), Dunlap, P. V. (2000) Quorum regulation of luminescence in Vibrio fischeri. In D. Bartlett (ed), Mol. Marine Microbial. Horizon Press, Norfolk, UK, Engebrecht, J., Nealson, K. and Silverman, M. (1983) Bacterial bioluminescence: Isolation and genetic analysis of functions from Vibrio fischeri. Cell 32, Engebrecht, J. and Silverman, M. (1986) Regulation of expression of bacterial genes for bioluminescence. In Genetic engineering Setlow, J.K. and Hollaender, A (eds), Plenum, New York, Fuqua, C., Parsek, M. R. & Greenberg, E. P. (2001) Regulation of gene expression by cell-to-cell communication: Acyl homoserine lactone quorum sensing. Annu. Rev. Genet. 35, Fuqua, C., Winans, S. C. & Greenberg, E. P. (1996). Census and consensus in bacterial ecosystems: the LuxR-LuxI family of quorum-sensing transcriptional regulators. Annu. Rev. Microbiol. 50, Gray, K.M., Passador, L., Iglewski, B.H. and Greenberg, E.P. (1994) Interchangeability and specificity of components from the quorum-sensing regulatory systems of Vibrio fischeri and Pseudomonas aeruginosa. J. Bacteriol. 176, James, S., Nilsson, P., James, G., Kjelleberg, S. and Fagerstrom, T. (2000) Luminescence control in the marine bacterium Vibrio fischeri: An analysis of the dynamics of lux regulation. J. Mol. Biol. Academic Press. 296, Kaiser, D. and Losick, R. (1993) How and why bacteria talk to each other. Cell, 73,

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