Synchronized DNA cycling across a bacterial population.

A defining goal of synthetic biology is to engineer cells to coordinate tasks that often require precise temporal modulation of gene expression. Although a variety of relatively small gene circuits have been constructed and characterized, their logical combination into larger networks remains a central challenge. This is due primarily to the lack of compatible and orthogonal elements for predictable dynamic control of gene expression. As an alternative approach to promoter-level regulation, we explored the use of DNA copy number as a circuit control element. We engineered colony-wide DNA cycling in Escherichia coli in the form of plasmid copy number oscillations via a modular design that can be readily adapted for use with other gene circuitry. Copy number modulation is a generalizable principle that adds a layer of control to synthetic gene circuits, allowing dynamic regulation of circuit elements without requiring specially engineered promoters.