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—also known as osmophoresis. In the case of metabolically active non-motile bacteria it is unclear how osmophoresis will be affected by a chemical reaction that can alter the concentration field and, therefore, the osmotic pressure gradient ‘sensed’ by the bacterium.