(385a) Living Oil-Water Interfaces: Buckling and Deformation of Droplets By Cell Growth at Finite Liquid Interfaces

Active matter systems consist of individual agents that require energy to self-propel or to exert a force on their surrounding environment. For certain concentrations and activity levels of the agents, the collective systems display unique material properties and the emergence of large-scale collective behaviors and phenomena. Here, we investigated the growth of rod-shaped bacteria on oil droplets of varying diameter in microfluidic chambers through direct visualization using time-lapse microscopy. Over the course of 36 hours, we observe that droplets above a critical diameter become living oil-water interfaces while droplets below a critical diameter undergo no change at all. The emergence of the rich behavior of living oil-water interfaces is a result of the coupling between adsorption and growth of bacteria at finite-area liquid interfaces. The interplay of bacteria morphology and interfacial curvature leads to the self-assembly of a monolayer of cells with long-range orientational order at the droplet surface. As cell division continues at the oil-water interface, stresses generated from growth and division leads to the emergence of self-sustained, long-range, meso-scale motion and deformation of the droplet surface, including wrinkling 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 and its potential influence on the transport of oil droplets in the ocean water column.