Transfer of noncoding DNA drives regulatory rewiring in bacteria

The rapid pace of evolution in bacteria is widely attributed to the promiscuous horizontal transfer and recombination of protein-coding genes. However, it has not been investigated if the same forces also drive the evolution of noncoding regulatory regions. Here, we establish that regulatory regions can “switch” between nonhomologous alternatives and that switching is ubiquitous, occurring across the bacterial domain. We show that regulatory switching has a strong impact on promoter architecture and expression divergence. Further, we demonstrate that regulatory transfer facilitates rapid phenotypic diversification of a human pathogen. This regulatory mobility enables bacterial genes to access a vast pool of potential regulatory elements, facilitating efficient exploration of the regulatory landscape.