Hands-Free Control of Heterologous Gene Expression in Batch Cultures

Autonomous control of heterologous gene expression can simplify batch-culture bioproduction by obviating the need for monitoring growth condition. Existing technologies include the uses of special media, wasteful cell-cell communication or biochemical sensors designed only for specific synthetic pathways. There is a need for simple, resource-efficient and general-purpose autonomous control system responding to changing growth condition in batch cultures.  

We exploited E.coli stationary-phase promoters as sensors for growth-phase transition in batch cultures. We used a recombinase switch to relay transcription signal between a stationary-phase promoter and an output heterologous gene. Specifically, transcription signal from the stationary-phase promoter triggers recombinase expression; recombinase enzyme then inverts a constitutive promoter that turns ON the output gene. We demonstrated that we could predict switching efficiency given measured promoter dynamic ranges and recombinase cassettes with standardized translation initiation elements. We showed that the recombinase switch amplifies signal fold change, lowers cell-to-cell signal variability and eliminates signal fluctuation.

We introduced an autonomous control system for heterologous gene expression. Our system uses stationary-phase promoters and recombinase switches to sense and relay endogenous signals during growth-phase transition. Unlike other existing technologies, our system does not require special media or resource-consuming production of cell-cell signaling molecules. Together, this work provides a simple, generic and efficient tool for batch-culture bioproduction.