Understanding the emergence of microbial collective behaviors in the wild

Groups of cells generate large-scale behaviors and form patterns over vastly larger scales than individuals can sense, making them a classic type of active matter. A fundamental problem in understanding natural active matter is that their activities take place in highly complex, heterogeneous environments. In the case of cells, these environments affect both how the individual cellular agents coordinate and the movement behaviors they exhibit. A classic form of active cellular matter is cellular slime molds, which after starvation use a biochemical environmental signal to coordinate aggregation into multicellular groups. Existing models capture how on flat, homogenous substrates this signal relay produces emergent, population-wide spiral waves that lead cells to aggregate. However, this behavior evolved in complex, three dimensional environments like soil. We have designed a naturalistic environmental system where we can quantify how cellular changes such as number and density and environmental features such as particle size perturb collective outcomes. By capturing the aggregation process in these transparent soil microcosms, we aim to explore two fundamental questions: (1) how do features of the environment, together with individual properties, shape collective outcomes? and (2) what allows collective behaviors to be robust to environmental heterogeneity?