Quorum Sensing in Microbes and their Function in Modulating Antibiotic Synthesis

Abstract

The intercellular communication, commonly called as Quorum Sensing (QS) or auto induction, has been attributed for various coordinative and community phenomena in Gram positive and Gram negative bacteria. The signalling is facilitated by diffusible signal, auto inducers, in response to population of neighbouring bacteria. Consequently, QS influences bacterial phenotype such as the production of antibiotics. Current understanding of how bacteria mediate antibiotic synthesis in the natural environment is limited to classical quorum sensing receptors and ‘orphan’ quorum sensing receptors. The genetic studies and biochemical investigation of carbapenem synthesis in Serratia and Erwinia carotovora have acknowledged a group of nine genes complex in the assembly namely carRABCDEFGH which are responsible for antibiotic assembly. N-(3oxohexanoyl)-L-homoserine lactone (OHHL) is produced as a product of the independent carI gene activates CarR transcription factor. This OHHL reliant transcriptional activation permits the cells to synchronise expression of carbapenem with cell density. An orphan quorum-sensing receptor, discovered as the soil bacterium Burkholderia thailandensis, differs from classical quorum sensing as this receptor does not respond to characteristic quorum sensing signalling partners. The orphan receptor however responds to antibiotics, such as trimethoprim and sulfamethoxazole. Consequently, eliciting the expression of the genes malA-M which is involved in synthesis of the cytotoxic antibiotic malleilactone. This controlling pathway might be vital to sense and compete in mixed communities. The synthesis of antibiotic is very expensive for the bacteria therefore the induction and modus of induction is tightly regulated. This work is an understanding of the current view of quorum sensing and their function in modulating antibiotics synthesis.