N-Acylhomoserine Lactones, Quorum Sensing, and Biofilm Development in Gram-negative Bacteria

Many different Gram negative bacteria employ N-acylhomoserine lactones (AHLs) as dif- fusible signal molecules which enable bacterial populations to co-ordinate gene expression as a function of cell population density. Such co-ordinated community behavior, termed "quorum sensing" (QS) regulates diverse physiological processes including secondary me- tabolite production, motility, DNA transfer and pathogenicity. AHLs are produced during the biofilm mode of growth and AHL-dependent QS influences the development, integrity and architecture of biofilm communities as well as orchestrating the optimal timing and production of secondary metabolites to combat predators and host defense mechanisms. In most cases the identity of the QS-regulated target structural genes which contribute to biofilm development have not yet been identified. However, the increased susceptibility of biofilms formed by Pseudomonas aeruginosa QS mutants to conventional antibacterial agents and host defenses highlights the utility of AHL-dependent QS as a novel antimi- crobial target.