3. Cost and specificity of cell–cell signalling
Quorum sensing (QS) or cell–cell communication is a process
of chemical communication among bacteria; it is defined as gene
expression in response to cell density, which influences various
functions, that is, virulence, acid tolerance and biofilm formation.
Because bacteria within biofilms reach a high cell density, QS is
considered one of the important bacterial functions [9]. Cell–cell
signalling results from the production of signalling molecules by
emitter cells and their accumulation in the surrounding environment. At some threshold concentration, the signalling molecules
bind to receptors on or in the bacterial cell, leading to changes in
gene expression in the responding cell (Fig. 3)