Speaker
Description
Biofilms are complex communities collectively organized by microbial cells embedded within an extracellular matrix. The analysis of biophysical interactions [1] between matrix environment and microbial cells [2] is an active topic in the field of bacterial multicellularity. Modelling of these extracellular environmental cues driving the biofilm formation require a revisit to fundamentals of biochemical transport phenomena and the underlying mechanistic actions. Over the past four decades, numerous standard mathematical models [1, 3, 4] have been developed to describe different stages of biofilm formation and predict substrate mass transport as a function of macroscale parameters such as biovolume and thickness of biofilm. However, they generally do not account for the interplay between microbial cell surface and the surrounding polysaccharides (PS) due to lack of any rate kinetics data at the microscale length scales [1, 2]. Our laboratory has recently developed expertise in leveraging super-resolution confocal microscopy to analyze distinct morphologies of extracellular environment in early-stage bacterial biofilms. We have thereby developed a new modelling platform based on emerging biofilm morphologies driven by the heterogeneous matrix environment.
We proposed a continuum particle geometry to theoretically conceptualize microbial cell (cell as core) to be surrounded by capsular matrix (polymeric capsule as shell), forming a "cell-capsule" structure. Our multiscale transport model [5] uses different particle packing arrangements that mimic the heterogeneous matrix structure. Considering initial adhesion of Staphylococcus sp. to the inert substratum as a case study, distinct structural features recorded recently in our laboratory clearly suggests capsule formation around the bacterial cell. By exploiting the above spatial distribution of bacterial capsule varying over time, cell concentration is determined using classical reaction-diffusion analysis. Different reaction kinetic expressions representing PS production and cell growth are coupled to cell diffusion in two-dimensional continuum space. Using a known history of the cellular characteristics in the inoculating feed with fixed cell diameter (ca. 1 μm), simulated versions of microcolonies of varying capsule thickness along the distance from the substratum are investigated.
Physiologically relevant estimates of particle flux provided preliminary evidence on how capsule structures are spatially arranged to produce an equivalent ‘resistance-in-series’ effect. Using the cell-capsule approach [5], we previously observed that the decrease in oxygen flux at steady-state conditions is likely due to the radially distributed patterns in biofilm morphology. By providing the quantitative data on these structured features with continuous time, an interesting trend of thick capsule formation as a potential survival mechanism to reduce the rate of cellular adhesion is proposed. Therefore, the above findings potentially complement ongoing experimental campaigns on how cell-scale morphogenesis controls the early-stage biofilm formation.
References:
1. Wanner, O., Eberl, H., Morgenroth, E., Noguera, D., Picioreanu, C., Rittmann, B. & Loosdrecht, M. V. Mathematical Modeling of Biofilms. IWA Publishing, UK (2006).
2. Drury, W. J., Characklis, W. G. & Stewart, P. S., Wat. Res., 27, 1119-1126 (1993).
3. Stewart, P. S., Biotechnol. Bioeng., 59, 261-272 (1998).
4. Xavier, J. B. et al., Microbiology,151, 3817–3832 (2005).
5. Moorthy, R.K. & Casey, E., arXiv (2025). DOI: 10.48550/arXiv.2510.19947