Growth-driven avalanche behavior in bacterial monolayers.

Growing bacterial colonies behave as active matter, with growth providing the activity. These colonies can take on granular properties such as microdomains. Based on this similarity, we perform a statistical analysis of pressure in simulated growing bacterial colonies under confinement, using methods commonly used to describe avalanches in driven granular materials and other intermittent systems. We find that as cells in a confined colony continue to grow, intermittent pressure drops occur alongside cell rearrangements. The statistics of these events have scaling exponents similar to mean-field predictions for avalanches in granular materials. This similarity suggests a new category of avalanche behavior, in which avalanches can be driven by single-particle growth rather than system-wide shearing or compression. These intermittent pressure-relieving cell rearrangements help explain how growing cell colonies can navigate complex environments with full confinement or growth bottlenecks.