Bacteria growth and self-organization at liquid interfaces can buckle and deform oil droplets

Bacteria growth, colony formation, and the emergence of structure in biofilms at interfaces are relevant to many natural and industrial processes. Here we present experimental work where we use microfluidics and time-lapse microscopy to examine the growth of rod-shaped bacteria on stationary oil droplets with maximum diameters ranging from 10 to 200 micrometers. After 72 hours, we observe that droplets above a critical diameter become living oil-water interfaces while droplets below a critical diameter do not change at all. The emergence of the rich behavior of living oil-water interfaces is a result of the coupling between the adsorption and growth of bacteria at finite-area liquid interfaces. The interplay between bacteria morphology and interfacial curvature results in the self-organization of a monolayer of cells with long-range orientational order at the droplet surface. As cell growth and division continue, the stress generated from cell-cell steric interactions gives rise to the emergence of mesoscale collective motion followed by the deformation of the droplet surface, including buckling and tubulation. This setup functions as a useful model system to gain insight into active stresses at deformable interfaces and improves our understanding of microbial oil biodegradation.