Quorum Sensing

Abstract

Quorum sensing has been known to regulate genes involved in various bacterial social behaviors such as biofilm formation, pathogenicity, motility, and antibiotic resistance. It is also associated with the enhancement of biofilm dispersion and upregulation in the synthesis of surfactant molecules. Intuitively, it may even appear to coordinate the switching mechanisms within the pattern of microbial interactions when the population outreaches the threshold. The standard quorum sensing pathway constitutes the microbial population communicating through signal molecules and behavioral genes. By remaining dormant until the population increases, these microbes overwhelm the host defense mechanism by activating the genes regulating microbial biofilm formation and end virulence. This cell-to-cell communication involves inter-/intracellular signaling pathways that coordinate and alter the degree of biofilm formation; involves physiological processes such as symbiosis, formation of spores, and antibiotic synthesis; and goes as far as genetic competence too. Not only this, but human pathogens such as Pseudomonas aeruginosa and other microbes too communicate with each other under quorum sensing. Thus, it regulates the evolution, virulence, motility, and formation of biofilms. Microbes, exhibiting quorum sensing, constitutively secrete few small clusters of amino acids and/or fatty acid derivatives (modified signaling molecules) collectively called autoinducers or pheromones. They also bear receptors that are distinctly susceptible to the detection of these pheromones, thus fully activating the receptors and forming a positive feedback loop within them. Quorum sensing facilitates coordination and carries diverse range of microbial functions such as bioluminescence, conjugation, competence, virulence, sporulation, and biofilm formation. These colonies engage in a pure “neighbor-to-neighbor communication” by secreting signaling molecules in a way that also depends on the population concentration of that particular microbial species. Hence, the quorum sensing system has rightly been recognized as an early step toward multicellularity.