Modelling the ecology of phototrophic-heterotrophic biofilms

• Published in: Communications in nonlinear science & numerical simulation 2021-03, Vol.94, p.105577, Article 105577
• Main Authors: Tenore, A., Mattei, M.R., Frunzo, L.
• Format: Article
• Language: English
• Subjects: Biofilms; Biomass; Colonization; Diffusion; Ecological effects; Free boundaries; Free boundary value problem; Heterotrophs; Industrial applications; Mathematical models; Microbiology; Microorganisms; Model accuracy; Model testing; Numerical simulations; Organic carbon; Parabolic differential equations; Partial differential equations; Phototrophic biofilm; Shading; Simulation; Substrates; Wastewater treatment
• ISSN: 1007-5704; 1878-7274
• DOI: 10.1016/j.cnsns.2020.105577

•A free boundary value problem for phototrophic biofilm growth is presented.•Microbial interactions between phototrophs and heterotrophs are considered.•Effect of light, organic carbon, EPS production and microbial invasion is investigated.•Numerical simulations provide results in agreement with experimental evidence. A mathematical model describing the microbial interactions in phototrophic-heterotrophic biofilms is presented. The main phenomena and factors involved in the model include: biomass growth and decay, substrates production, diffusion and consumption, biological invasion of planktonic species and detachment. In particular, non linear hyperbolic PDEs describe the growth of the microbial species while quasi-linear parabolic PDEs govern the dynamics of substrates and invading species. The whole system of PDEs is considered in a free boundary domain. The following syntrophic interactions are also modelled: the exchange of dissolved oxygen, organic carbon and inorganic carbon produced and released by phototrophs and heterotrophs, respectively. The positive effect of heterotrophic pioneers on the phototrophic growth is modelled by introducing a phototrophic colonization rate depending on the EPS fraction in the biofilm. Numerical simulations are performed to test model accuracy. Simulation results reproduce the main symbiotic mechanisms between phototrophs and heterotrophs reported in literature, such as the positive effect of heterotrophic pioneers and their EPS production on phototrophic growth and the effects of phototrophic organic carbon release on the invasion and growth of heterotrophic bacteria. Furthermore, model results highlight the role played by heterotrophic species under photoinhibition conditions, which provide a positive shading contribution to phototrophic growth. Light is confirmed as the most significant factor in the ecology of phototrophic-heterotrophic biofilms. Such results confirm the accuracy of the model that correctly predicts the evolution of a phototrophic-heterotrophic biofilm and the main phenomena involved, and can be seen as an auxiliary tool in different industrial applications, such as wastewater treatment and bioenergy production.