Quorum Sensing-Controlled Gene Expression Systems in Gram-Positive and Gram-Negative Bacteria

Abstract

In this chapter, quorum sensing (QS)-controlled gene expression systems in Gram-positive and Gram-negative bacteria is particularly emphasized. Acyl homoserine lactone (AHL) autoinducer (AI)-mediated signalling is a communication system in Gram-negative bacteria that control specific genes expression imparting physiological characteristics such as biofilm formation, bioluminescence, antibiotic synthesis, plasmid transfer, virulence factor, metal resistance and hydrocarbon degradation. AI concentrations reach a threshold level when adequate bacterial density is present that allows sensing a critical cell mass and in response they activate or repress target genes expression. Strikingly, AI binds the LuxR-type proteins, triggering them bind DNA and activate transcription of target genes. Synthesis of the AHL is dependent on a luxI homologue and a luxR homologue encoding a transcriptional activator protein, which is accountable for recognition of the cognate AHL and expression of correct gene. Gram-positive bacterial QS systems typically use secreted small oligopeptides via a dedicated ABC (ATP-binding cassette) exporter protein and two-component systems, which involve membrane-bound sensor kinase receptors and transcription factors present in cytoplasm which is responsible for alterations in gene expression. The process of signal transduction takes place as a phosphorelay cascade.