Cooperative colonization of the host and pathogen dissemination involves stochastic and spatially structured expression of virulence traits

Bacteria respond to changing environments by altering gene expression. Some responses display probabilistic cell-to-cell variation within isogenic populations. A few paradigmatic examples in animal pathogens have demonstrated that this phenotypic heterogeneity has biological relevance for virulence.

We investigate single-cell flagellar expression in relation to type III secretion expression in the plant pathogen Pseudomonas syringae and describe that both systems undergo phenotypic heterogeneity throughout plant colonization. We establish that high expression of these system carries growth penalties. Stochastic, spatial and time factors shape dynamics of a phenotypically diverse population which displays division of labor during colonization: T3SS ^ON bacteria effectors act as ‘common goods’ to suppress immunity, allowing the increase of motile bacteria that actively leave the infected tissue before necrosis. This study provides a comprehensive view of how processes underlying bacterial specialization play out in the context of complex and changing environments of biological and applied relevance such as host colonization.