Bacterial biofilms are multi-cellular microbial  communities  formed at  air-water or solid-water interfaces.  Notable, the community is always embedded in  self-produced extracellular polymeric substances (EPS). One of the most  interesting and yet little understood aspects of biofilm growth  is the form and function of their complex,  heterogeneous structure.  We are interested in obtaining  a better understanding of biofilm structure and use mathematical modelling combined with laboratory experiments to address this problem.

In this talk,  we will discuss a simple model for  a single substrate-limited biofilm, which grows into an aqueous environment.  The model considers the biofilm as a complex fluid and the process of growth is reduced to a consideration of a moving interface driven by pressure resulting from  cell division.  We show  that planar front solutions are admitted by this model and moreover that under certain conditions,  these are linearly unstable to non-planar perturbations. We show  that  cell death rate is a key factor in determining stability of the growth front. Somewhat counter-intuitively, we establish that greater rates of cell death lead to a destabilization of planar growth.  Using numerical techniques centred on the level set method, we show that once the planar front has been destabilized, fingering subsequently  occurs. Finally, we discuss  experiments that we conducted  to investigate the observed differences in growth dynamics between wild type and EPS mutant strains. We  hypothesize that this is due to differences in the ability to absorb and /or retain water.