Engineering the esaR promoter for tunable quorum sensing- dependent gene expression.

Quorum sensing (QS) systems enable bacteria to coordinate their behavior as a function of local population density and are often used in synthetic systems that require cell−cell communication. We have engineered the esaR promoter， P(esaR)， which is repressed by the QS regulator E(saR). E(saR)-dependent gene expression from P(esaR) is induced by 3-oxo-hexanoyl-homoserine lactone (3OC6HSL). Here， we report a set of modified P(esaR) promoters that contain a second E(saR) binding site. We observed changes in gene expression levels， regulatory range， 3OC6HSL sensitivity， and the regulatory role of E(saR) that are dependent on the position of the second binding site. Combining the new promoters with endogenous 3OC6HSL production led to QS-dependent systems that exhibit a range of expression levels and timing. These promoters represent a new set of tools for modulating QS-dependent gene expression and may be used to tune the regulation of multiple genes in response to a single QS signal.