Sensing- and Communication-Dependent Control of Microbial Motility

The long-term goal of this project is to enable the use of microorganisms for the controlled motion of micron-scale devices, known as microrobots. A key aspect of his design is the generation of strain of E. coli where motility is tightly regulated by a cell-cell communication, or quorum sensing (QS) signal. The second biological module will be a strain, or combination of strains, that recognize extracellular signal(s) and produce the QS signal recognized by the first strain. This approach is advantageous because the sensor strains can easily by swapped to recognize different signals or combined to recognize multiple signals, or perform more complex computation. The use of QS may also be useful for amplifying the signal when low concentrations of a target molecule are present. We have constructed a strain of E. coli, where its swimming motility is tightly controlled by the esa QS system. The esa system provides advantages over the well-known lux system because its regulator, EsaR, can act as a repressor, which leads to lower levels of background expression. This is expecially important when controlling genes where only a few copies can enable a change in phenotype. In this case, we have used EsaR to control the expression of a key motor protein. The ribosome binding site was also engineered to optimize the control of the expression of the motor protein and enable QS-dependent motility. In swim plate assays, we have shown that our new construct shows no swimming motility in the absence of QS signal. Interestingly, we have also observed directional swimming, where the swimming cells move up a gradient of QS signal generated by a second strain of cells producing the signal.