Modeling biofilm complexity by including active and inert biomass and extracellular polymeric substances

Abstract

We present an overview of all the features of the unified multi-component cellular automaton (UMCCA) model. The UMCCA model describes quantitatively the complexity of biofilms for all biofilm components: active bacteria, inert biomass and extracellular polymeric substances (EPS). It also includes original donor substrate, two types of soluble microbial products (SMP) and oxygen. All mass balances and parameters used in UMCCA are based on our unified theory, which reconciles the apparently disparate findings about active and inert biomass, EPS and SMP. The UMCCA model captures all trends observed experimentally regarding biofilm density, namely large density differences within individual biofilm samples, with bottom layers (closest to the substratum) being as much as 5 to 10 times denser than top layers, which appear to be “fluffy” and porous. To capture this effect, the UMCCA model employs the novel idea of biofilm consolidation: the fluid over the biofilm creates pressures and vibrations that cause the biofilm to consolidate, or pack itself to a higher density over time. As a result, each biofilm compartment in the model output consolidates to a different degree that depends on the age of its biomass, which is higher for the bottom layers of the biofilm. The UMCCA model can also be used to describe biofilm mechanical properties variable in time and space, and it can be linked to finite-element software to study the behavior of biofilms under tensile or compressive stress and to perform a stress analysis of the deformed biofilm, possibly indicating where it is likely to fail or detach.