Effect of dispersants on bacterial colonization of oil droplets: a microfluidic approach

TL;DR

This study uses microfluidics to observe how dispersants affect bacterial colonization of oil droplets, finding that dispersants do not significantly influence attachment or growth processes, which are mainly driven by diffusion and droplet size.

Contribution

The paper provides direct microscopic evidence that dispersants do not alter bacterial attachment or growth on oil droplets, clarifying their role in biodegradation.

Findings

Dispersants do not inhibit bacterial attachment or growth.

Attachment time depends on droplet size and diffusion.

Diffusive encounters primarily drive colonization.

Abstract

Bacteria biodegradation of immiscible oil requires cell-droplet encounters, surface attachment, and hydrocarbon metabolism. Chemical dispersants are applied to oil spills to reduce the mean dispersed droplet size, thereby increasing the available surface area for attachment, in attempts to facilitate bacterial biodegradation. However, their effectiveness remains contentious as studies have shown that dispersants can inhibit, enhance, or have no effect on biodegradation. Therefore, questions remain on whether dispersants affect surface attachment or cell viability. Here, using microfluidics and time-lapse microscopy, we directly observe the attachment and growth of the marine bacterium, \emph{Alcanivorax borkumensis}, on stationary crude oil droplets ($5$ \textmu m $< R < 150$ \textmu m) in the presence of Corexit 9500. We show that the average colonization time, or the time comprised of encounters, attachment, and growth, is dependent on droplet size and primarily driven by diffusive encounters. Our results suggest that dispersants do not inhibit or enhance these biophysical processes.