Abstract

The term quorum sensing in bacteria is used to describe the communication among them through signalling molecules, known as autoinducers or pheromones. This type of communication usually triggers at a time when the bacteria reach their threshold population. This in turn leads to expression of various genes, resulting in co-operative behaviour in bacteria. Biofilm formation, virulence expression are the examples of such kind of quorum sensing. In Gram-negative bacteria such as Pseudomonas aeruginosa, quorum sensing is achieved through acyl homoserine lactone class of signalling molecules, two such molecules are 3-oxo-dodecanoylhomoserine lactone and butylhomoserine lactone. The productions of these molecules are controlled by LasI and RhlI genes through the acylhomoserine lactone synthetases. At high concentration, those signal molecules bind to cytoplasmic transcription factors LasR and RhlR and activate target genes leading to expression of virulence factors namely elastase, protease, rhamnolipids, pyocyanin, siderophores. In Pseudomonas aeruginosa, the Las and Rhl systems function in tandem with the Las system at the top and these two systems are interconnected by Pseudomonas quinoline signal. Quorum sensing in bacteria can be inhibited by targeting either signal generator, the signal molecule or the signal receptor. Quorum sensing inhibitors can be obtained from natural sources including traditional medicines or can be synthesized in the laboratory.