Repulsion from slow-diffusing nutrients improves chemotaxis towards moving sources

Abstract

AbstractChemotaxis, or the following of chemical concentration gradients, is essential for microbes to locate nutrients. A microbe can swim in the direction of increasing nutrient concentrations to reach the source. However, microbes often display paradoxical behaviors, such asEscherichia colibeing repulsed by several amino acids. Here, we explore chemotaxis towards a moving target and demonstrate that repulsion from a nutrient can actually improve chemotaxis towards its source. Because a moving source leaves most of the nutrient plume behind it, simply following the concentration gradient produces inefficient intercept trajectories. However, when attraction to a fast-diffusing molecule and repulsion from a slow-diffusing molecule are combined, motion in a new direction emerges and intercept times are significantly reduced. When the source is moving faster than the microbe can swim this differential strategy can even be essential to ever intercepting the source at all. Finally, we leverage existing data to show thatE. coliis attracted to fast-diffusing amino acids and repulsed by slow-diffusing ones, suggesting it may utilize a differential strategy and providing a possible explanation for its repulsion from certain amino acids. Our results thus illuminate new possibilities in how microbes can integrate signals from multiple concentration gradients and propose a new strategy by which microbe may accomplish the difficult task of intercepting a moving target.