Emerging morphologies in round bacterial colonies: comparing volumetric versus chemotactic expansion
Biological experiments performed on living bacterial colonies have demonstrated the microbial capability to develop finger-like shapes and highly irregular contours, even starting from an homogeneous inoculum. In this work, we study from the continuum mechanics viewpoint the emergence of such branched morphologies in an initially circular colony expanding on the top of a Petri dish coated with agar. The bacterial colony expansion, based on either a source term, representing volumetric mitotic processes, or a nonconvective mass flux, describing chemotactic expansion, is modeled at the continuum scale. We demonstrate that the front of the colony is always linearly unstable, having similar dispersion curves to the ones characterizing branching instabilities. We also perform finite element simulations, which not only prove the emergence of branching, but also highlight dramatic differences between the two mechanisms of colony expansion in the nonlinear regime. Furthermore, the proposed combination of analytical and numerical analysis allowed studying the influence of different model parameters on the selection of specific patterns. A very good agreement has been found between the resulting simulations and the typical structures observed in biological assays. Finally, this work provides a new interpretation of the emergence of branched patterns in living aggregates, depicted as the results of a complex interplay among chemical, mechanical and size effects.
KeywordsBacteria colony growth Branching instability Bacterial chemotaxis Volumetric growth
We are grateful to Davide Ambrosi for helpful discussions.
- Ben Amar M (2013) Chemotaxis migration and morphogenesis of living colonies. Eur Phys J E Soft Matter 36(6). doi: 10.1140/epje/i2013-13064-5
- Flemming HC, Wingender J (2010) The biofilm matrix. Nat Rev 8:623–633Google Scholar
- Guyon E, Hulin JP, Petit L, De Gennes PG (2001) Hydrodynamique physique. EDP Sciences, Les UlisGoogle Scholar
- Hamill OP, Martinac B (2001) Molecular basis of mechanotransduction in living cells. Phys Rev 81(2):685–740Google Scholar
- Kozlovsky Y, Cohen I, Golding I, Ben-Jacob E (1999) Lubricating bacteria model for branching growth of bacterial colony. Phys Rev E Phys Plasmas Fluids Relat Interdiscip Top 50:7025–7035Google Scholar