Marco Mazza

Topological Transitions in Active Spaghetti: from Motion to Structure

Many active systems are capable of forming intriguing patterns at scales significantly larger than the size of their individual constituents. Cyanobacteria are one of the most ancient and important phyla of organisms that has allowed the evolution of more complex life forms. Despite its importance, the role of motility on the pattern formation of their colonies is not understood. A primary example is the formation of reticulate patterns.

We investigate the large-scale collective effects and rich dynamics of gliding filamentous cyanobacteria colonies, while still retaining information about the individual constituents’ dynamics and their interactions [1-2]. Theoretical arguments predict the characteristic length scale of the emerging reticulate pattern with no fitting parameters.

We investigate both the colony’s transient and steady-state dynamics and find good agreement with experiments. We furthermore show that the Péclet number and aligning interaction strength govern the system’s topological transition from an isotropic distribution to a state of large-scale reticulate patterns. Although the system is topologically non-trivial, the parallel and perpendicular pair correlation functions provide structural
information about the colony, and thus can be used to extract information about the early stages of biofilm formation. Our model proves to reproduce both cyanobacteria colonies and systems of biofilaments where curvature is transported by motility.

[1] M. K. Faluweki , J. Cammann , M. G. Mazza , and L. Goehring, "Active Spaghetti: Collective Organization in Cyanobacteria", Phys. Rev. Lett. 131, 158303 (2023).
[2] J. Cammann, M. K. Faluweki, N. Dambacher, L. Goehring, M. G. Mazza, "Topological transition in filamentous cyanobacteria: from motion to structure", Commun. Phys. 7, 376 (2024).