Modelling biofilm dynamics

Biofilms are communities of bacteria and other small organisms that form a spatial structure like the black slime you get in taps and garden hoses. They can have important implications for health in some circumstances, for example by causing disease or by fouling medical implants. People with cystic fibrosis are often infected by the bacterium Pseudomonas aeruginosa. In order to survive, Pseudomonas aeruginosa needs iron, which it imports by secreting molecules called siderophores that bind the iron and then reabsorbing them. Each bacterium can absorb siderophores secreted by any other bacterium, and in fact there are mutant strains of P. aeruginosa that `cheat’ by absorbing siderophores, but not producing any. The cheats gain an advantage over the cooperative wild-type bacteria, because they don’t put energy into siderophore production and so are able to outcompete the wild-type locally as long as enough wild types remain to produce sufficient siderophores for everyone. This cooperator-cheat dynamics may lead to more persistent P. aeruginosa infections.

When P. aeruginosa cooperator and cheat strains are grown together in the lab, segregation of the two types leads to spatial patterns. This project will use mathematical and computational modelling to investigate the spatial patterning in order to understand its causes and potential consequences for bacterial persistence. The models that we develop will span multiple scales from the scale of an individual P. aeruginosa bacterium up to the level of a bacterial colony on which pattern formation is observed, incorporating not only exchanges of chemicals - such as siderophores and nutrients - between the bacteria and their environment, but also physical interactions with their surrounding medium and substrate resulting from effects such as colony growth and fluid flow.

The theoretical work will develop in close cooperation with biologists Dr Jose Jimenez and Dr Alexandra Penn studying this system in the lab (https://surreysynbio.wordpress.com/research-interests/) so that both theory and experiment benefit from an exchange of ideas.