Microbial two-component glue to engineer self-healing pipes; The Pico-Plumber

Layperson Summary: This synthetic biology project will engineer a bacterium from the human gut, Escherichia coli, to detect and fix leaking pipes. Engineered E. coli will detect leaks by homing in on a chemical signal released at the leak site. As the bacteria migrate towards the leak, they will synthesise two proteins, one on the outside of the cell, the other inside, which represent the two components of a biological, protein glue. The adhesive is only activated when the two components mix. The E. coli cells will be engineered to burst at the leak site, mixing the two glue components and creating a sticky protein plug to repair the pipe.

Scientific summary

Synthetic biology approaches are being used in a novel iGEM project that will engineer E. coli to detect and repair leaks and corrosion in pipes. The bacterium will respond by migrating to the site of the leak and plugging the breach using a protein-based glue. This solution could be used to seal leaks in pipes in inaccessible places, for example within a nuclear power station cooling system, or on a space station. The novelty of the biological engineering lies in the implementation of a two-component glue to seal the pipe, analogous to an epoxy resin that is only activated when two components, an adhesive and hardener, are mixed. In this project E. coli is engineered to synthesise the glue components (tropoelastin and lysyl oxidase) in different cellular compartments, which are then mixed following autolysis of the bacterium. The relative timings of the elastin glue synthesis and autolysis steps are carefully controlled, thus ensuring regulated lysis, but only after tropoeleastin/lysyl oxidase synthesis.

To achieve these aims, E. coli will be engineered to respond to an inducer molecule (IPTG) released from the site of a pipe breach. In this project, our model pipes will have a surface coating of the inducer and the attractant aspartate, which are only released into the pipe in the case of a breach in the wall. Once the inducer IPTG is sensed by the bacterium, lacI repression will be relieved, inducing expression of tropoelastin (adhesive) within the E. coli, and the enzyme lysyl oxidase (the adhesive hardener) on the cell surface. This will be achieved by expressing lysyl oxidase as a translational fusion with the outer membrane protein OmpX. Motile E. coli will be used to allow chemotactic migration of the tropoelastin-expressing E. coli to the site of the pipe breach.

The expression of tropoelastin within the cytoplasm, and lysyl oxidase on the cell surface, will maintain the glue components in separate compartments. Their mixing at the site of pipe breach will be achieved by regulated autolysis, triggered by the lytic peptide T4 holin, initiating a cross-linking reaction and the formation of elastin. However, holin expression will be delayed relative to that of tropoelastin and lysyl oxidase, to allow the manufacture of glue components before cell lysis and glue mixing is initiated. This temporal delay will be achieved by using IPTG to induce a molecular inverter element that switches off a repressor of holin production. Slow decay in the levels of this repressor will trigger eventual holin synthesis thereby allowing cell lysis and tropoelastin/lysyl oxidase mixing.

This project is designed in a modular way; individual components will be mathematically modelled and their design improved, before being built and tested. The separate testing of these modules will ensure that the project will not be compromised should any one module perform unpredictably. At the same time, the dependence of the project on the carefully staged expression of different gene modules will ensure a challenging research project for our theoreticians and biologists alike, who will work together to improve and implement the design of a novel two-component microbial glue for use in self-healing pipes.