Motile Bacteria at Oil–Water Interfaces: Pseudomonas aeruginosa

Abstract

Bacteria are important examples of active or self-propelled colloids. Because of their directed motion, they accumulate near interfaces. There, they can become trapped and swim adjacent to the interface via hydrodynamic interactions, or they can adsorb directly and swim in an adhered state with complex trajectories that differ from those in bulk in both form and spatiotemporal implications. We have adopted the monotrichous bacterium Pseudomonas aeruginosa PA01 as a model species and have studied its motion at oil–aqueous interfaces. We have identified conditions in which bacteria swim persistently without restructuring the interface, allowing detailed and prolonged study of their motion. In addition to characterizing the ensemble behavior of the bacteria, we have observed a gallery of distinct trajectories of individual swimmers on and near fluid interfaces. We attribute these diverse swimming behaviors to differing trapped states for the bacteria in the fluid interface. These trajectory types include Brownian diffusive paths for passive adsorbed bacteria, curvilinear trajectories including curly paths with radii of curvature larger than the cell body length, and rapid pirouette motions with radii of curvature comparable to the cell body length. Finally, we see interfacial visitors that come and go from the interfacial plane. We characterize these individual swimmer motions. This work may impact nutrient cycles for bacteria on or near interfaces in nature. This work will also have implications in microrobotics, as active colloids in general and bacteria in particular are used to carry cargo in this burgeoning field. Finally, these results have implications in engineering of active surfaces that exploit interfacially trapped self-propelled colloids.

Driven and active colloids at fluid interfaces

“…These different orientations of the body with respect to the interface are associated with distinct motility patterns (Deng et al. 2020). More complex biohybrid colloids of P. aeruginosa adhered to polystyrene microbeads also exhibit a wide range of persistent, complex motions at fluid interfaces (Vaccari et al.…”

Wetting/spreading on porous media and on deformable, soluble structured substrates as a model system for studying the effect of morphology on biofilms wetting and for assessing anti-biofilm methods

“…Chemotaxis and surface sensing can influence directionality and motility mechanisms. Analysis of trajectories of P. aeruginosa PA01 (monotrichous bacteria, propelled by a single flagellum located at the pole at one end of the cell body) in an oil/water emulsion [62] evidenced four distinct characteristic motions, summarized in Table 2: In the initial phase (0-5 hours), the biofilm grew predominantly in the lateral plane and cells shown a Brownian and random walk. As the biofilm develops (5-10 hours), individual cells shown persistent and straight trajectories, which dominate the bulk of the biofilm at the later stage (10-15 hours).…”

Physical Transport Processes that Affect the Distribution of Oil in the Gulf of Mexico: Observations and Modeling

“…Some, but not all, of the observations suggest that the ability to form such elastic films relies on the ability of the bacteria to metabolize the oil phase (Niepa et al, 2017). Bacteria near interfaces display a range of behaviors that includes Brownian motion, swimming in circular trajectories, and directed swimming (Deng et al, 2020). These motions can also enhance the dispersion and transport of micron-scale droplets (Vaccari et al, 2018).…”