Oskar Hallatschek, Ph.D.
, associate professor, University of California, Berkeley
In natural settings, microbes tend to grow in dense populations where they need to push against their surroundings to accommodate space for new cells. The associated contact forces play a critical role in a variety of population-level processes, including biofilm formation, the colonization of porous media, and the invasion of biological tissues. Although mechanical forces have been characterized at the single cell level, it remains elusive how single-cell forces combine to generate population-level patterns. Hallatschek presents a synthesis of theory and microbial experiments that show that contact forces generated by microbial populations can become very large due to a self-driven jamming mechanism. These forces feed back on the physiology of the cells and can strongly perturb the mechanical integrity of the environment, thereby promoting microbial invasion. Finally, Hallatschek highlights that the cooperative nature of microbial force generation induces a screening effect that reduces the selection against slower growing mutant types. These results underscore that, in crowded microbial populations, collective phenomena often have a mechanical basis.