Abstract

The development of a multicellular organism can be thought of as a series of hierarchical patterning events, dividing groups of cells into nested domains that give rise to tissues, organs, and specialized cell types. By building gene regulatory circuits that are capable of patterning populations of microbes, we can investigate the minimal genetic architecture required for this most basic developmental process and build synthetic developmental systems that can be used as a platform for future engineering. A requirement for circuits built according to the patterning model proposed by Alan Turing in 1952 (and a generally useful addition to the genetic toolkit) is the use of two independent diffusible signals. We have engineered promoters for use in E. coli that minimize crosstalk between two exogenous quorum-sensing signaling systems and used those promoters to parameterize a model of signaling within the two pathways present in the same cell. By using this two-channel signaling system we were able to build a genetic regulatory circuit in which cells sending and receiving either signal repress the ability to send and receive the other signal, resulting in bistability on the population level—that is, cells come to a collective decision about which signaling state they are in. This leads to the formation of spatial domains of gene expression both at the level of colonies, and in larger populations.