Many of the stunning morphologies that distinguish living entities do not arise exclusively from gene expression programs, but rather from overarching contributions from mechanical forces. Such morphomechanical processes include the formation of ripple-shaped leaves, tendrils and flowers, as well as villi formation in our gut and sulci development in our brain. Though ancient in their evolutionary origin, bacterial cells can also display intricate developmental patterns, particularly when they grow as biofilms on soft substrates such as agar (Yan et al. 2019).
Movie 1: Growth of a V. cholerae biofilm on medium containing 0.7% agar. Imaging began 5 hr after inoculation and has a total duration of 75 hr with 15 min time steps. The field of view is 41.5 mm × 27.7 mm.
By combining quantitative imaging, biomaterial characterization, mutant analyses, and mechanical theory, we show that the mismatch between the growing biofilm layer and the non-growing substrate causes mechanical instabilities that enable the biofilm to transition from a flat to a wrinkled film, and subsequently to a partially detached film containing delaminated blisters. Our results demonstrate that bacterial biofilms provide a uniquely tractable system for the quantitative investigation of mechanomorphogenesis, and opens rational design principles for morpho-engineering. We are now investigating how geometrical constraints and surface topography influence the mechanical instabilities during biofilm development and the subsequent biofilm morphology.