Phenotypic Variability Shapes Bacterial Responses to Opposing Gradients

Although bacterial chemotaxis behavior in a single gradient has been well studied, chemotaxis of bacterial population in complex environments is not well understood. Here, we discovered four distinct behaviors of Escherichia coli populations in microfluidic experiments with different opposing gradients of MeAsp and serine. By using a population chemotaxis model based on the dynamics of intracellular signaling pathways, we found that the nongenetic variability of the relevant chemoreceptors (Tar and Tsr) within the population is responsible for the diverse population behaviors. Through analyses combining the phenotype-to-performance mapping and Tar/Tsr ratio distribution, we predicted the phase diagram of population chemotaxis behaviors under varying chemical gradients and the effect of growth period on population behaviors, which were verified by additional experiments. Our study suggests that phenotypic heterogeneity in chemoreceptors enables diverse chemotactic strategies, which cells may adopt to improve their population fitness in complex environments.