Modeling multispecies biofilms including new bacterial species invasion

•Invasion model of new species into multispecies biofilms is presented.•1D model is discussed first and then generalized to 3D.•Qualitative properties of solutions show the consistency of the model.•No conditions for biofilm species concentrations are assigned on the free boundary.•Simulations for a known example show the model can predict colonizing process.

A mathematical model for multispecies biofilm evolution based on continuum approach and mass conservation principles is presented. The model can describe biofilm growth dynamics including spatial distribution of microbial species, substrate concentrations, attachment, and detachment, and, in particular, is able to predict the biological process of colonization of new species and transport from bulk liquid to biofilm (or vice-versa). From a mathematical point of view, a significant feature is the boundary condition related to biofilm species concentrations on the biofilm free boundary. These data, either for new or for already existing species, are not required by this model, but rather can be predicted as results. Numerical solutions for representative examples are obtained by the method of characteristics. Results indicate that colonizing bacteria diffuse into biofilm and grow only where favorable environmental conditions exist for their development.