Tuning the Dials of Metabolite Biosensors

Genetically-encoded biosensors trigger expression of target genes in response to metabolites or small molecules. They offer great potential for diverse applications such as dynamic pathway engineering, environmental sensing, and real-time metabolic monitoring. Biosensors can be fine-tuned by modifying their DNA sequences, yet so far we have a poor grasp of how such tuning shapes the resulting dose-response curve. We built and characterized promoter libraries in E. coli controlled by metabolite-responsive transcription factors, and asked how changes in the operator sequence shape the biosensor's dose-response curve. Our data from the lactose and arginine systems revealed that the biosensors' dynamic range and response threshold are inherently coupled to one another. Mathematical modelling revealed a highly nonlinear relation between dynamic range and threshold, exhibiting maximum achievable limits for both parameters. Combining theory and experiments we uncovered two other tuning dials that provide orthogonal control of the dose-response curve. Our work sheds light on the limits of synthetic biology designs and provides guidelines for biosensor design in metabolic engineering.

* Di Liu and Ahmad Mannan contributed equally to this work.

* Correspondence: fzhang@seas.wustl.edu, d.oyarzun@imperial.ac.uk