Research On Biofilm Growth Dynamics

Various species of bacteria form highly organized spatially-structured aggregates known as biofilms. Biofilm formation is a mutual protection strategy through the interaction of microorganisms lived in, it is benefit for the microorganisms and responsible for infections in tissues and medical implants and fouling of pipes and industrial equipment. Whereas their growth can be desirable in industrial setting such as wastewater treatment, bioremediation and microbial fuel cells. So it is important to investigate the growth dynamics of the biofilm formation in order to control and make full use of it. We inoculate the Wild-type and strain incapable of producing expolysaccharide (EPS mutant) Bacillus subtilis biofilm on an agar plate with MSgg medium and get the 2D thickness maps through image processing by the MATLAB software. To understand how microenvironments impact biofilm growth dynamics and reveal the relationships among different biophysical process in the biofilm growth process, we proposed a diffusion-reaction continuum model to simulate the formation of Bacillus subtilis biofilm on an agar plate. The extended finite element method combined with level set method are employed to perform the simulation, numerical results show the quantitative relationship between colony morphologies and the rate limiting nutrient depletion over time. Predictions of the glutamate source biofilm's shape parameters agree with the experiment mutant colony better than that of glycerol source biofilm, suggesting that glutamate is rate limiting nutrient for Bacillus subtilis biofilm growth on agar plate, and the diffusion-limited regime is a better description to the experiment. Numerical experiment indicate that maximum radius and thickness are of linear relationship with its initial nutrient concentration, whereas of nonlinear relationship with maximum consumption rate during biofilm formation on agar plate. Moreover, the osmotic pressure gradients generated by the production of the expolysaccharide push wild-type expansion form the bulk, whereas cell-cell contact drives expansion of the matrix-deficient mutant form the leading edge. Control over the shape and transition is an invaluable opportunity for the wild-type biofilm to increase nutrient uptake. In addition, we found that the diffusion time scale is of the same magnitude as growth process, and the common-employed quasi-steady approximation is not applicable here. The model framework could be used to study the phenotype transition related to the nutrient depletion and the channel transportation in the winkled biofilm.