This work consists of two main projects: the first project describes bacterial confinement within a thin but resilient layer of liquid. The second project reports on the analysis of transient attachment and detachment of bacteria from a solid surface by applying an external electric field. In the study of flagellated bacteria trapped within thin films of liquid, I describe observations of bacteria moving in circular trajectories when they are confined within a thin layer of water around dispersed micrometer-sized particles sprinkled over a semi-solid agar gel. In this setting, E. coli and Enterobacter sp. orbit around the dispersed particles in clockwise paths. The liquid layer is shaped like a shallow tent with its height at the center set by the seeding particle and the meniscus profile set by the strong surface tension of water. The thin fluid layer is resilient due to a balance between evaporation and reinforcement of fluid that permeated out of the agar. The latter is driven by the Laplace pressure caused by the concave meniscus. In the second project, I report an experiment for Caulobacter crescentus weakly attached to a plastic surface and subjected to an electric field parallel to the surface. I observe that some individuals transiently, but repeatedly attach to the surface. While electrophoretically driven by the field, these bacteria move significantly slower than the unattached ones and their speeds exhibit large variations, frequently dropping close to zero for short intervals of time. This study sheds light on the process of bacterial interaction with surfaces and suggests applying electric field as a useful method to investigate bacteria-surface interaction.
