[CCoE Notice] CHE ENG: Narendra Dewangan PhD Defense Update

[Knudsen, Rachel W]

NAME: Narendra Dewangan



COMMITTEE CHAIR: Dr. Jacinta Conrad



DATE: Tuesday, December 08, 2020



TIME: 10:00 AM Central Time (US and Canada)



LOCATION:

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Meeting ID: 799 1921 3797
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TITLE:

Bacterial Adhesion and Motility at Oil-Water Interfaces

Abstract:



Degradation of hydrocarbons by bacteria is one of the most important process in oil spill remediation. During oil spills, chemical dispersants are often deployed to increase the surface area per unit volume of oil available to bacteria. Biofilm formation is one of the important pathways in degradation of oil by bacteria. Because adhesion of bacteria to surface is one of the important steps in biofilm formation, it is important to understand the factors that affect the bacterial adhesion on oil/water interfaces. Adhesion of bacteria on solid surfaces is widely studied, but, surprisingly, how bacteria adhere on the oil/water interface, and the effect of surfactants and bacterial motility on this process remains incompletely understood. In this thesis, we developed methods to examine the adhesion of bacteria on oil droplets immersed in water. We used Marinobacter hydrocarbonoclasticus SP17 and Halomonas titanicae bead 10BA, isolated from the Gulf of Mexico after the 2010 Deepwater Horizon oil spill, as model bacteria. We prepared oil/water emulsions using a glass-based coflow microfluidic device and attained drop sizes of 15 µm – 300 µm. M. hydrocarbonoclasticus bacteria preferentially adhered to smaller dodecane droplets, and the number of cells adhering at the oil-water interface followed the first-order Langmuir adsorption as the cells diffused towards the interfaces by Brownian motion. The number of adhering cells at the interface decreased as the surfactant concentration is increased. For a fixed droplet size the areal density of bacteria at the interface decreased with increasing surfactant concentration, due to a reduction in oil-water interfacial tension that increased the free energy of adhesion of the bacterium. The use of anionic surfactants led to a sharp reduction in adhesion with increasing concentration as compared to cationic and nonionic surfactants, which we attributed to electrostatic interactions between droplets and bacteria. Motile bacteria exhibited higher adhesion to oil droplets due to enhanced mobility. Finally, we showed that adhered motile bacteria are able to rotate oil droplets located near a solid wall due to hydrodynamic interactions. The angular speed of droplets was altered by the concentrations of bacteria and surfactant and by the interfacial affinity of the bacteria. An improved understanding of how surfactants and motility affect adhesion of bacteria to oil in the early stages of biodegradation is expected to inform scenarios such as efficient use of dispersants in oil spill cleanup and removal of pollutants from wastewater.
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