E. coli Motility in a Confined Channel with Asymmetric Surface Properties

Abstract

In nature environment, bacterial swimming motility is important clinically since chronic bacterial infection and biofilm formation rely on the swimming capacity of bacteria. Also they want to swim in the confined environment such as medical devices, soil, organ and blood vessel to maximize the contact of their body to the surface. Therefore, as time goes by, many biologists and physicists have expended research topics towards the study of bacterial behavior in confined space. However, many studies were explained by population model. Interaction between individual bacterial motility and the surface is still not understood deeply. Especially, research of the swimming bacterial motility on the hydrophobic surface have not studied well. Therefore, study of the individual-cell model is required to understand and control the bacterial motility on the surface fundamentally. In this thesis, a microfluidic chip with asymmetric surface properties is developed to observe the individual bacterial motility depending on the different hydrophobicity of one surface. As a result, different hydrophobicity of one surface affect the bacterial swimming speed, surface, angle, and staying time. When one surface hydrophobicity is increased, bacterial average swimming speed is decreased due to many stopped bacteria. In case of the swimming surface, surprisingly, swimming bacteria tend to switch to the opposite surface. When one surface hydrophobicity is decreased, bacteria tend to swim along the surface continuously without switching. While the bacteria continue to swim along the same surface, their swimming direction angle was measured and the maximum-fraction among the swimming direction angles was slightly larger or smaller (5 ~ 15º difference) than straight direction (90º). Besides, interestingly, staying time which was peculiar behavior of bacteria was observed under condition of the surface with contact angle of 80º. These new phenomena will be useful for studying the additional bacteria swimming pattern and understanding the interaction between bacteria surface and substrate. Overall, this thesis about individual bacteria motility depending on the surface properties can be greatly impactful for future studies such as controlling bacterial motions.