title: Emerging morphologies in round bacterial colonies: comparing volumetric versus chemotactic expansion.
abstract: 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.
authors: MOX - Politecnico di Milano and Fondazione CEN, Piazza Leonardo da Vinci 32, 20133, Milan, Italy.
authors: Chiara
authors: C
authors: Giverso
authors: MOX - Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milan, Italy.
authors: Marco
authors: M
authors: Verani
authors: CNRS and Institut Jean le Rond d'Alembert, UMR 7190, Université Paris 6, 4 Place Jussieu, Case 162, 75005, Paris, France. pasquale.ciarletta@polimi.it.
authors: Pasquale
authors: P
authors: Ciarletta
mesh_terms: D001419:Bacteria / Q000166:cytology* / Q000254:growth & development; D002633:Chemotaxis; D003198:Computer Simulation; D008954:Models, Biological; D009716:Numerical Analysis, Computer-Assisted; D011312:Pressure
keywords: Bacteria colony growth; Bacterial chemotaxis; Branching instability; Volumetric growth