Regulation of bacterial locomotion at oil-water interfaces*

The locomotion of P. aeruginosa at the interface between oil and bacterial suspensions is studied. At solid surfaces, it is well established that bacteria experience hydrodynamic and adhesion forces that inhibit flagellar rotation. Such changes in flagellar motility initiate different processes such as EPS secretion and ultimately biofilm formation. However, hydrodynamic boundary conditions and interfacial forces differ from those on solid boundaries. Here, we study effect of fluid interfaces and structure formation on the regulation of the bacterial motility. The rheology of the interface evolves over time due to the adsorption of polysaccharides and bio-surfactant. These changes in interface mechanics alter the motion of cells adhered to and adjacent to the interface. Trajectories of bacteria are studied to analyze their velocity, reorientation, and dispersion coefficient. We investigate 3 different strains and mutations of P. aeruginosa to study effect of interfacial rheology on the bacterial behavior. These include (i) PA14ΔpelA, selected as a control strain as it does not restructure the interface; (ii) PA01 ΔpelA which does not secret polysaccharides but forms viscoelastic film; and (iii) wild type PA01 which makes a highly elastic film of bacteria at the interface.