| Cells process external information and make complex behavioral decisions by networks of interacting signaling proteins. The creation of synthetic cellular circuits with the ability to mimic complex behavior found in cells is becoming increasingly common. The current paradigm for tuning synthetic biological systems is through reengineering system components. Biological systems designed with the inherent ability to be tuned by external stimuli will be more versatile. We have engineered E. coli cells to behave as an externally-tunable band-pass filter for enzyme activity and small molecules. The genetic circuit enabled bacterial growth to be patterned in response to chemical gradients in nonintuitive ways and facilitated the isolation of engineered allosteric enzymes. A new class of switches, termed phenotypic switches, was identified through the use of this band-pass filter and characterization indicates that ligand-induce stabilization is responsible for the switching behavior. Using the band-pass filter, we attempted to isolate a sucrose specific switch from a library of switch mutants. Although unsuccessful, evidence suggests that many members in this library may be phenotypic switches and that an altered screening strategy might yet identify a sucrose specific switch. |
