Growth and roughening of biofilms*

Biofilms are complex self-assembling structures formed by bacteria and extracellular polymeric substances (EPS). Biofilm structure not only provides mechanical advantages, but increased resistance to antibiotics, protection to predation and starvation. Biofilms adhere to a solid interface and grow unconstrained towards a fluid medium. The evolution of this free surface is set by a complex array of mechanical interactions on multiple scales, and is limited by nutrient and spatial availability. Using high-resolution interferometry we study the evolution of surface growth and fluctuations of Vibrio cholerae strains with different rates of EPS production. The interface is then characterized according to its fractal dimension and roughness to account for its local and global features. We compare our experimental data with PDE models, such as the Kardar-Parisi-Zhang equation and a simple biomass transfer model. These results provide evidence that optical profiling of biofilm surfaces can be used as an alternative for the analysis of developing biofilms without the need of genetic engineering and fluorescence microscopy.