Tubulation and dispersion of oil by growth of marine bacteria on oil droplets

Bacteria on surfaces exhibit collective behaviors such as active turbulence and active stresses, which result from their motility, growth, and interactions with the local surroundings. However, interfacial deformations on soft surfaces and liquid interfaces caused by active growth, particularly over long time scales, are not well understood. Here, we describe experimental observations on the emergence of tubular structures arising from the growth of rod-shaped bacteria at the interface of oil droplets in water. Using microfluidics and time-lapse microscopy, we quantify the dimensions and growth rates of individual tubular structures as well as bulk biofilm formation on hundreds of droplets over 72 hours. We find that tubular structures are composed of an inner filament of oil stabilized by an outer shell of bacteria and are comparable in size to the initial droplet radius. These oil filaments then undergo breakup into smaller microdroplets dispersed within the bacterial shell. Finally, we describe how oil tubes, microdroplets, and bacteria break off from the droplet into its surroundings. This work provides insight into active stresses at deformable interfaces and improves our understanding of oil biodegradation and its influence on the transport of oil droplets in the ocean.