Abstract

Bacteria often live in the form of dense aggregates such as biofilms. It is therefore important to characterize dense states of bacteria, but is also challenging because in many cases it is experimentally difficult to realize a uniform growth condition for dense populations. Here we overcome this by a membrane-based device that we recently developed [1] and report the emergence of glassy states in two-dimensionally confined motile Escherichia coli [2]. We find that the system undergoes two separate glass transitions as packing fraction is increased, first the glass transition for the orientation degrees of freedom and second that for the translational ones. We characterize this bacterial glass transition and discuss similarities and dissimilarities compared with usual glass formers. If time allows, I also discuss the case of nonmotile E. coli under soft two-dimensional confinement, where topological defects turned out to influence structure and dynamics of bacterial populations [3]. [1] T. Shimaya et al., Commun. Phys. 4, 238 (2021) https://doi.org/10.1038/s42005-021-00739-5 [2] H. Lama et al., arXiv:2205.10436 https://doi.org/10.48550/arXiv.2205.10436 [3] T. Shimaya and K. A. Takeuchi, PNAS Nexus 1, pgac269 (2022) http://dx.doi.org/10.1093/pnasnexus/pgac269