Microbial Quorum Sensing: Linking the Outside World to Microbial Behaviour

Dear Colleagues,

Bacteria “communicate” with each other by using signalling molecules, a process called “quorum sensing” (QS). This form of signal dependent communication is present in Gram-positive and Gram-negative bacteria, as well as in fungi. At low population density only basal amounts of signal molecules are produced, not provoking an effect. At a certain threshold, signal concentrations will be high enough resulting in a binding to signal receptors and ultimately in an altered gene expression. Many micro-organisms apply their QS system(s) for the coordination of virulence and biofilm formation and/or maturation. The most commonly-used signaling molecules are N-acyl-homoserine lactones (AHL) that are produced by many Gram-negative bacteria. The autoinducer-2 (AI-2) QS system is considered to be a universal system used for interspecies communication and allows bacteria not only to sense the density of members of their own species, but also to sense the total density of a mixed community. The QS system of Gram-positive bacteria generally consists of a signal peptide and a two-component regulatory system made up of a membrane-bound sensor and an intracellular response regulator. QS systems in Gram-positive bacteria are much more diverse than the Gram-negative AHL QS system and there are many variations in the nature of the QS signal. In addition, some bacteria use alfa-hydroxy-ketone signaling molecules (including cholera autoinducer 1 and Legionella autoinducer 2), signaling molecules belonging to the "diffusible signal factor" family or quinolones of the PQS family. Finally, signaling molecules like tyrosol and farnesol can be sensed by fungi and can regulate group behaviour in these organisms.
This Special Issue of "Sensors" aims to cover the different aspects of cell-cell communication and how microorganisms use this quorum sensing to regulate their behaviour.

Prof. Dr. Tom Coenye
Guest Editor