A long term ambition of our project is to contribute to the understanding of biofilms by engineering model cell interaction networks.

A biofilm is a thin layer of tightly packed microorganisms that adhere to, solid surfaces to form colonies. In many cases the colonies are comprised of several different species of bacteria. The microbes are encapsulated within a self-produced matrix, EPS, which is made up of DNA, proteins and polysaccharides.

Biofilms are unique because unlike normal free-floating bacteria, the close cellular proximity in the biofilm causes the microbes to exhibit cooperative behaviour. As a result, the microorganism communities are comparable to multi-cellular organisms.

This behaviour causes biofilms to be very resilient against attack and hence when biofilms develop within humans or domestic animals they can be resistant to antibiotic treatments. When left undisturbed, biofilms build up on surfaces and can become potentially harmful.

In order to develop more effective ways of removing biofilms, scientists need to discover more about the cooperative behaviour exhibited by the cell communities.

There are three basic forms of cell interaction that take place in a biofilm matrix: negative, neutral and positive interaction.

In our project, we have used a rock-paper-scissors (RPS) model to demonstrate a particular type of interaction network. Our bacteria are engineered to disable the primary plasmids of the opponent cells and not to kill the cells, hence this demonstrates an example of neutral cell interaction, which is thought to be the primary interaction that stabilises biofilms.

In 2002, Kerr et al published a paper in Nature that investigated how the local dispersal of cells promotes biodiversity. To illustrate this theory, they developed a RPS model where the cells destroy one another whereby exhibiting negative interaction.

A continuation of our iGEM project would be to expand the RPS system to examine how auto-inducers from neighbouring cells could interact with the core metabolism of cells; an example of positive cell interaction.

Once the different forms of cell interaction have been modelled and verified in model systems, scientists will gain a greater insight into biofilm behaviour and control.