Abstract

Abstract: Position-dependent gene expression is a critical aspect of the development and behaviour of multicellular organisms. It requires a complex series of interactions to occur between different cell types in addition to intracellular signalling cascades. We used Escherichia coli to study the properties of an artificial signalling system at the interface between two expanding cell populations. We genetically engineered one population to produce a diffusible acyl-homoserine lactone (AHL) signal, and another population to respond to it. Our experiments demonstrate how such a signal can be used to reproducibly generate simple visible patterns with high accuracy in swimming agar. The producing and responding cassettes of two such signalling systems can be linked to produce a symmetric interface for bidirectional communication that can be used to visualise molecular logic. Intracellular feedback between these two cassettes would then create a framework for self-organised patterning of higher complexity. Adapting the experiments of Basu et al. (Basu et al., 2005) using cell motility, rather than a differential response to AHL concentrations as a way to define zones of response, we noted how the interaction of sender and receiver cell populations on a swimming plate could lead to complex pattern formation. Equipping highly motile strains such as E. coli MC1000 with AHL-mediated autoinducing systems based on Vibrio fischeri luxI/luxR and Pseudomonas aeruginosa lasI/lasR cassettes would allow the amplification of a response to an AHL signal and its propagation. We designed and synthesised codon-optimised auto-inducing luxI/R and lasI/R cassettes as optimal gene expression is crucial for the generation of robust patterns. We still have to complete and test the entire genetic circuitry, although by modelling the system we were able to demonstrate its feasibility. Aims Our aim was to induce self-organised pattern formation in free swimming bacteria with techniques of genetic engineering. This was to be done by artificially introducing a system for bi-directional communication between two bacterial populations. Escherichia coli cells would be equipped with genes derived from independent quorum sensing systems from Pseudomonas aeruginosa and Vibrio fischeri. These systems can facilitate both communication between cell populations and regulated switching between competing cell fates. The negotiation of cell fates within bacterial populations can be visualised precisely by expression of different fluorescent proteins. Proposed system In our proposed system Modelling We built models for our proposed genetic system at both unicellular and multicellular levels. The single-cell model describes the transcription and translation activities inside a cell containing either type 1 or type 2 genetic circuitry. Assuming that both types of cells are similarly efficient in transcription and translation, the model characterises the