(6bc) Active colloids at the oil-water interface: The biophysics of microbial oil degradation

In natural habitats, microbes regularly encounter a wide variety of interfaces that influence their behavior and activity. Bacteria often accumulate near interfaces and will eventually attach to them. In favorable conditions, bacterial will grow and divide leading to colonization of the interface. Dense colonies formed at the liquid-solid interface are referred to as biofilms while those formed at the liquid-gas interface are referred to as pellicles. Bacterial colonies also form at the liquid-liquid interface, for example at the oil-water interface, although the process is not well understood. Biofilms can be undesirable and destructive causing infection and biofouling, however, they can be beneficial in the production of biofuels and environmental processes such as waste water treatment. Bacterial attachment to an interface is the first step in colonization, therefore understanding the mechanisms of bacterial attachment will provide controlled methods to prevent or enhance biofilm formation.

My research interests are broadly in the field of experimental soft condensed matter physics. My doctoral research (with Richard Lueptow and Julio Ottino, Northwestern University) focused on mixing and segregation dynamics of granular mixtures in rotating tumblers. My postdoctoral research (with Paulo Arratia, UPenn) focused on establishing a link between the molecular microstructure and the macroscopic rheological properties of complex polymeric fluids. My current research (with Roman Stocker, MIT) focuses on understanding the fundamental interactions between microbes and liquid-liquid interfaces, specifically the biodegradation of crude oil by marine bacteria. The degradation of oil in the ocean is a process of immense societal and ecological importance whose efficiency ultimately hinges on fundamental problems in colloidal and interface physics because degradation occurs when individual bacteria attach to individual oil drops.

I will discuss experimental and theoretical results on the effect of oil drop diameter on the attachment of marine bacteria to the oil-water interface. Using phase-contrast and fluorescence microscopy, we directly observed the dynamics of marine bacteria in the presence of oil droplets of varying diameter within microfluidic devices. We find that microbial growth and degradation become strongly limited for drops smaller than a critical diameter. A theoretical model of attachment supports this finding, suggesting that rendering oil droplets too small by the excessive addition of dispersants, as often done in oil spills, might be a counterproductive strategy. This research aims to pursue a deeper understanding of the fundamental oil-microbe interactions and promises to open the door to a broad set of other problems in interfacial physics, hydrocarbon microbiology, and other oil spill management related questions.