Chemotaxis as a navigation strategy to boost range expansion

Bacterial chemotaxis, the directed movement of cells along “chemoattractant” gradients, is among the best-characterized subjects of molecular biology(1–10). Much less is known about its physiological roles(11). Commonly, it is seen as starvation response when nutrients run out, or as escape response from harmful situations(12–16) . Here, we establish an alternative role of chemotaxis by systematically examining the spatiotemporal dynamics of Escherichia coli in soft agar(12,17,18): Chemotaxis in nutrient-replete conditions promotes the expansion of bacterial populations into unoccupied territories well before nutrients run out in the current environment. We show how low levels of chemoattractants act as aroma-like cues in this process, establishing the direction and enhancing the speed of population movement along the self-generated attractant gradients. This navigated range expansion process spreads faster and yields larger population gains than unguided expansion following the canonical Fisher-Kolmogorov dynamics(19,20) and is therefore a general strategy to promote population growth in spatially extended, nutrient-replete environments.