Tubulation and dispersion of oil by bacterial growth on droplets

TL;DR

This study investigates how bacterial growth on oil droplet interfaces causes tubulation and dispersion, revealing active stress effects and implications for microbial oil degradation and droplet transport in aquatic environments.

Contribution

It provides the first detailed experimental analysis of bacterial-induced tubulation and oil dispersion at soft interfaces over long time scales.

Findings

Tubular structures grow to sizes comparable to initial droplet radius.

Oil filaments break into microdroplets within bacterial shells.

Active stresses influence interface deformation and droplet behavior.

Abstract

Bacteria on surfaces exhibit collective behaviors, such as active turbulence and active stresses, which result from their motility, growth, and interactions with their 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 timelapse microscopy, the dimensions and extension rates of individual tubular structures as well as bulk bio-aggregate formation are quantified for hundreds of droplets over 72 hours. Tubular structures are comparable in length to the initial droplet radius and are composed of an outer shell of bacteria that stabilize an inner filament of oil. The oil filament breaks up into smaller microdroplets dispersed within the bacterial shell. This work provides insight into active stresses at deformable interfaces and improves our understanding of microbial oil biodegradation and its potential influence on the transport of droplets in the ocean water column.