Characterization and orthogonality assessment of two quorum sensing systems for synthetic biology applications

Quorum sensing systems have a broad range of applications within the field of synthetic biology. However, a bottleneck is the optimization and tuning of these systems due to the lack of standardization and complete characterization. In this research, two quorum sensing systems, namely the LasI/LasR and the EsaI/EsaR system, were fully characterized in the model host organism Escherichia coli. Furthermore, insight was gained in the interplay between the various parts of these systems. To further expand the range of possibilities with these quorum sensing systems, the orthogonality of the two systems was assessed to allow simultaneous use within the same cell without interfering crosstalk. This assessment was performed on three levels: promoter, signal and synthase crosstalk. It was demonstrated that LasR is able to interact with the promoter of the EsaI/EsaR system, albeit to a low extent. Additionally, LasR was able to respond to the autoinducers produced by EsaI. To solve the promoter crosstalk, a nucleotide change was introduced into the binding site of EsaR within the promoter region. Additionally, LasR mutants were created rationally and screened for decreased response to EsaI while retaining functionality. The best performing mutant, LasR(P117S), was further characterized. In conclusion, we have further unlocked the potential of quorum sensing systems for synthetic biology applications by obtaining two functional, characterized and orthogonal quorum sensing systems.