Bacterial chemotaxis to a finite localized source

Chemotaxis, or the ability to sense and respond to chemical gradients, is crucial in microorganisms to forage new food, colonize uncharted territories, and find hosts and symbionts. In nature, chemotaxis often occurs in heterogeneous settings characterized by fluid flows, variable porosity, and patchy distributions of nutrients and microbes. Here, we use a transparent granular medium that mimics confined environments such as soil or the human gut to spatially pattern nutrient distributions and examine how an ephemeral nutrient source influences bacterial chemotaxis. We find that whether the bacteria accumulate or form a chemotactic band depends on the cell density and the size of the attractant. These studies not only shed light on chemotaxis in the real world but also provide a framework for engineering bacterial suspensions for bioremediation applications.