Quorum sensing is a regulatory system used by bacteria for controlling gene expression in response to increasing cell density.¹This regulatory process manifests itself with a variety of phenotypes including biofilm formation and virulence factor production.²Coordinated gene expression is achieved by the production, release, and detection of small diffusible signal molecules called autoinducers. The N-

acylated homoserine lactones (AHLs) comprise one such class of autoinducers, each of which generally consists of a fatty acid coupled with homoserine lactone (HSL). Regulation of bacterial quorum sensing signaling systems to inhibit pathogenesis represents a new approach to antimicrobial therapy in the treatment of infectious diseases.³AHLs vary in acyl group length (C₄-C₁₈), in the substitution of C3 (hydrogen, hydroxyl, or oxo group), and in the presence or absence of one or more carbon-carbon double bonds in the fatty acid chain. These differences confer signal specificity through the affinity of transcriptional regulators of the LuxR family.⁴In the gram-negative bacteriumA. tumefaciens, N-3-oxo-octanoyl-L-homoserine lactone promotes the expression of the transcriptional activator (and LuxR homolog) TraR.⁵

References
1. González, J.E., and Keshavan, N.D. Messing with bacterial quorum sensing Microbiol. Mol. Biol. Rev. 70(4), 859-875 (2006).
2. Gould, T.A., Herman, J., Krank, J., et al. Specificity of acyl-homoserine lactone syntheses examined by mass spectrometry Journal of Bacteriology 188(2), 773-783 (2006).
3. Cegelski, L., Marshall, G.R., Eldridge, G.R., et al. The biology and future prospects of antivirulence therapies Nature Reviews.Microbiology 6(1), 17-27 (2008).
4. Penalver, C.G.N., Morin, D., Cantet, F., et al. Methylobacterium extorquens AM1 produces a novel type of acyl-homoserine lactone with a double unsaturated side chain under methylotrophic growth conditions FEBS Letters 580, 561-567 (2006).
5. Zhu, J., Beaber, J.W., Moré, M.I., et al. Analogs of the autoinducer 3-oxooctanoyl-homoserine lactone strongly inhibit activity of the TraR protein of Agrobacterium tumefaciens Journal of Bacteriology 180(20), 5398-5405 (1998).