In unity towards complex structures

Filamentous cyanobacteria aggregate in areas with favorable light conditions and use the light energy for photosynthesis. Typically, these microorganisms form long filaments consisting of many cells. However, the thread-like structures can only move forward or backward -- when leaving the illuminated area, they reverse their movement and thus remain in the light. Scientists at MPI-DS have investigated the resulting organizational structures. It was found that only the mutual interaction of several filaments causes the cyanobacteria to align themselves along the inner edge of the illuminated surface, thereby forming stable structures.

To do this, the researchers prepared and illuminated several cultures of cyanobacteria in Petri dishes. Using slides, they created different light patterns and subsequently observed the self-organization of the bacteria. With a circular light pattern, the bacteria mainly gathered at the edge of the illuminated area. Likewise, when the illuminated area was triangular, trapezoidal or otherwise shaped, characteristic patterns of filaments near the edge of the light emerged. "The remarkable thing is that the bacteria also arrange themselves along complex structures and curves, although they can only move back and forth," says Stefan Karpitschka, group leader at MPI-DS and professor at the University of Konstanz. "This is a typical example of emergence -- a characteristic overall structure arises independently at a higher level from the individual behavior of a single filament," he continues.

The insights gained from the scientists' experiments and the resulting model can also be applied to living matter with comparable morphology. "The model does not include any specific details regarding the biology of the bacteria," says Leila Abbaspour, joint first author of the study together with Maximilian Kurjahn. "This collective effect can thus also be observed in similar systems and enable active filaments to structure themselves according to sensory cues from their environment despite one-dimensional motility," Kurjahn continues.

The results of this study therefore provide important insights that may be used in the design of so-called smart textiles or materials, for example. These novel structures and tissues are also based on the arrangement of individual fibers and active filaments. Such mechanisms of self-assembly may thus enable the development of new innovative materials.