Module 1: Detection

Description | Design | Construction | Characterisation | Modelling | Conclusions

Description

The Detection Module enables our bacteria to detect plastic and respond by upregulating production of an adhesive (Module 2) for the aggregation of plastic fragments. Module 2 (Aggregation) requires the Detection Module because our adhesive proteins (curli fibrins) exhibit non-specific binding, and require a separate module to ensure that curlis are produced only when plastic is present. Without linking curli production in some way to the presence of plastic, there would be erroneous binding (to non-plastics), which would reduce the efficiency of our system.

As there is no fully characterised gene or sequence for a plastic receptor, we cannot transform our bacteria with a gene to detect plastic directly.

However, it is possible to detect plastic indirectly. Our Detection system relies on detecting a particular subgroup of organic molecules that harbour the tendency to adhere to plastic surfaces. These molecules are called Persistant Organic Pollutants (POPs). As they adhere to the surface of plastic, they can be used as an indicator. Collision of our bacteria with a plastic fragment will bring it into contact with the adhered POPs, and trigger the apparatus for adhering to plastic.

The same property that binds POPs to plastic – hydrophobicity – also allows them to pass through the bacterial cell membrane. Within, our bacteria will be carrying a genetic circuit, which encodes genes for detecting and reacting to the presence of POPs. Detecting will be achieved by constitutively expressing the regulator NahR, which transcriptionally activates synthesis of the curli operon through P(sal).

In the absence of a receptor for plastic itself this is the best possible way we have designed to detect plastic, and regulate the production of curlis.