Effect of EPS on biofilm structure and function as revealed by an individual-based model of biofilm growth

We have simulated a nitrifying biofilm with one ammonia and one nitrite oxi dising species in order to elucidate the effect of various extracellular po lymeric substance (EPS) production scenarios on biofilm structure and funct ion. The individual-based model (IbM) BacSim simulates diffusion of all sub strates on a two-dimensional lattice. Each bacterium is individually simula ted as a sphere of given size in a continuous, three-dimensional space. EPS production kinetics was described by a growth rate dependent and an indepe ndent term (Luedeking-Piret equation). The structure of the biofilm was dra matically influenced by EPS production or capsule formation. EPS production decreased growth of producers and stimulated growth of non-producers becau se of the energy cost involved. For the same reason, EPS accumulation can f all as its rate of production increases. The patchiness and roughness of th e biofilm decreased and the porosity increased due to EPS production. EPS d ensity was maximal in the middle of the vertical profile. introduction of b inding forces between like cells increased clustering.