(248i) Reaction-Driven Propulsion of Bacteria

Recent studies have shown that the 'non-motile' bacteria Syntrophus aciditrophicus has the ability to sense its chemical environment?an essential step for chemotaxis typically observed in 'motile' microorganisms (e.g., Escherichia coli). In light of these findings, new questions arise. Could self-propulsion take place naturally in non-motile metabolically active bacteria without the aid of external gradients or forces? What conditions are necessary for this to occur? These questions motivate us to propose a simple model for self-propulsion of a 'non-motile' metabolically active bacterium in the presence of an uniform reactant concentration. It has been observed that a biological cell permeable to fluid molecules but not to solutes?a semipermeable membrane?moves away from concentrated regions. This phenomenon results from an imbalance in the osmotic pressure between the two fluids separated by a cell membrane, leading to a fluid flow from inside the cell to high concentration regions in the outer fluid and from low concentration regions in the outer fluid to inside the cell. Such motion is known as osmophoresis. In the case of metabolically active non-motile bacteria it is unclear how osmophoresis will be affected by a chemical reaction at the surface of the cell that can alter the concentration field and, therefore, the osmotic pressure gradient ?sensed' by the bacterium. In this study, we consider an asymmetric surface chemical reaction at the bacterium surface (e.g., degrading transmembrane enzymes) causing a local osmotic pressure gradient autonomously and thus fluid flow across the membrane. We demonstrate that this fluid flow propels the bacterium toward less concentrated regions and that its velocity depends on the reaction speed, its size, and membrane and solvent properties.