Modeling of Symbiotic Bacterial Biofilm Growth with an Example of the Streptococcus-Veillonella sp. System.

We present a multi-dimensional continuum mathematical model for modeling the growth of a symbiotic biofilm system. We take a dual-species namely, the Streptococcus-Veillonella sp. biofilm system as an example for numerical investigations. The presented model describes both the cooperation and competition between these species of bacteria. The coupled partial differential equations are solved by using an integrative finite element numerical strategy. Numerical examples are carried out for studying the evolution and distribution of the bio-components. The results demonstrate that the presented model is capable of describing the symbiotic behavior of the biofilm system. However, homogenized numerical solutions are observed locally. To study the homogenization behavior of the model, numerical investigations regarding on how random initial biomass distribution influences the homogenization process are carried out. We found that a smaller correlation length of the initial biomass distribution leads to faster homogenization of the solution globally, however, shows more fluctuated biomass profiles along the biofilm thickness direction. More realistic scenarios with bacteria in patches are also investigated numerically in this study.

Numerical investigation on the role of check dams with bottom outlets in debris flow mobility by 2D SPH.

Check dams with bottom outlets are widely used in debris flow gullies to minimize the damage caused by debris flows. However, the bottom size is often based on empirical criteria due to the lack of knowledge of the interaction between the debris flow and the check dam with the bottom outlet. In this study, the interaction between a viscous debris flow and check dams with bottom outlets is investigated via flume tests using 2D smoothed particle hydrodynamics. The normalized height of the bottom outlet is varied from 0 to 1, and slope angles from 15 to 35° are considered. Based on the numerical results, the jump height decays with the increasing normalized height of the bottom outlet and this trend can be approximated by a power law function. When the normalized height of the bottom outlet is less than 0.15, the performance is similar to that of a closed check dam. The flow regulation and sediment trapping functions of the check dam may fail when the normalized height of the bottom outlet is greater than 0.6. These results show that the energy breaking, flow regulation, and sediment trapping functions of check dams with bottom outlets operate well when the normalized height of the bottom outlet is in the range 0.15-0.6. Even if model limitations require further efforts to validate the findings of this study, they provide a basis for the rational design of check dams with bottom outlets.

Biofilm formation by the oral pioneer colonizer Streptococcus gordonii: an experimental and numerical study.

For decades, extensive research efforts have been conducted to improve the functionality and stability of implants. Especially in dentistry, implant treatment has become a standard medical practice. The treatment restores full dental functionality, helping patients to maintain high quality of life. However, about 10% of the patients suffer from early and late device failure due to peri-implantitis, an inflammatory disease of the tissues surrounding the implant. Peri-implantitis is caused by progressive microbial colonization of the device surface and the formation of microbial communities, so-called biofilms. This infection can ultimately lead to implant failure. The causative agents for the inflammatory disease, periodontal pathogenic biofilms, have already been extensively studied, but are still not completely understood. As numerical simulations will have the potential to predict oral biofilm formation precisely in the future, for the first time, this study aimed to analyze Streptococcus gordonii biofilms by combining experimental studies and numerical simulation. The study demonstrated that numerical simulation was able to precisely model the influence of different nutrient concentration and spatial distribution of active and inactive biomass of the biofilm in comparison with the experimental data. This model may provide a less time-consuming method for the future investigation of any bacterial biofilm.