Quorum Machinery: Effect of the las System in rhl Regulation of P. aeruginosa

Quorum sensing (QS) describes a communication mechanism via signal molecules that allows colonies of bacteria to coordinate gene expression. The nature of the QS system depends very much on the species. Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that has a highly complex QS system. The QS signalling system of P. aeruginosa is known to involve multiple control components, notably las, rhl and pqs systems. The QS signalling system of P. aeruginosa is responsive to two chemically different signal molecules, based on Homoserine-Lactones (HSLs) and 4-quinilines (4Qs). This paper focuses on the relation of the first two systems that manage Homoserine-Lactone (HSL) production since this is the main chemical signalling in P. aeruginosa that regulates many activities of bacteria, including symbiosis, virulence factors, motility, production of antibiotics, and formation of biofilm. The las and rhl system of P. aeruginosa do not act independently. Some gene expression that is regulated by rhl system is also controlled by the las system. Previous research has demonstrated that the las system can give rise to excitable pulse generation of signal molecule production. This paper examines the mechanism of how las and rhl systems act in tandem to generate sophisticated control on QS system of P. aeruginosa. Using analytic methods, it is shown how dynamics of the rhl system is affected by dynamics of the las system.