Resolving the Conflicts between Phenotypic Diversity and Collective Migration in Bacterial Populations

Project SummaryCell populations often display substantial phenotypic diversity, even in homogeneousenvironments. At the same time, biological functions are not typically carried out by isolated cells,but rather by populations of varying functional abilities. The conflicts between phenotypic diversityand collective behavior have scarcely been examined. This project will address the gap in ourunderstanding of these conflicts using Escherichia coli, a well-studied model system that exhibitsboth individuality and collective behavior. Groups of E. coli in a uniform field of nutrient formmigrating bands mediated by the well-characterized chemotaxis system, which enables them tochase a gradient of nutrient generated by their consumption. However, single cells in an isogenicpopulation of E. coli climb standing gradients with very different drift speeds, as recentlycharacterized by the Emonet lab. How are these cells able to migrate together? We recentlydiscovered a compensatory mechanism in which the fastest gradient-climbers localize to the frontof the traveling band where the gradient is shallow, and the weakest performers localize to theback where the gradient is steep. But not all phenotypes are able to travel, indicating thatcollective migration can limit the amount of phenotypic diversity in the population. Here, I willexamine the mechanisms by which bacteria resolve the conflicts between phenotypic diversityand collective behavior. Aim 1 will determine how phenotypic diversity in the band shapes thetraveling gradient of attractant, and how receptor adaptation together with the shape of thegradient in turn affect which phenotypes can travel. The results will produce a quantitativeunderstanding of how bacteria use spatial organization to resolve the conflicts betweenphenotypic diversity and collective behavior. Aim 2 will determine how differential growth andleakage of phenotypes off the back of the group affect collective migration. These studies willdeepen our understanding of the extent to which growth can counteract the effects of collectivebehavior on population diversity.