Biomechanics and Modeling in Mechanobiology

, Volume 15, Issue 3, pp 643–661 | Cite as

Emerging morphologies in round bacterial colonies: comparing volumetric versus chemotactic expansion

Original Paper


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.


Bacteria colony growth Branching instability Bacterial chemotaxis Volumetric growth 



We are grateful to Davide Ambrosi for helpful discussions.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Chiara Giverso
    • 1
  • Marco Verani
    • 2
  • Pasquale Ciarletta
    • 3
  1. 1.MOX - Politecnico di Milano and Fondazione CENMilanItaly
  2. 2.MOX - Politecnico di MilanoMilanItaly
  3. 3.CNRS and Institut Jean le Rond d’Alembert, UMR 7190Université Paris 6ParisFrance

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