Noise and kinetics of LuxR positive feedback loops.

We have previously reported the design and construction of positive feedback loops (PFLs) based on the LuxI-LuxR quorum-sensing system that can be used as modular transcriptional regulatory units for the construction of complex artificial genetic circuits. Here, we characterize these PFLs using single-cell and dynamic induction studies to fully understand their behavior and facilitate their incorporation into novel networks. The LuxR PFLs had graded responses to the OHHL signal molecule with inductions developing over time, causing a lag in response compared to a non-feedback control. The properties of the PFLs could be altered using LuxR mutants with altered sensitivities without changing the inherent properties of the systems. Because of their high sensitivity and ability to establish intercellular signaling, the LuxR PFLs described in this work could be used as well-defined modules for the construction of artificial genetic circuits.