Quorum sensing regulation in Erwinia carotovora affects development of Drosophila melanogaster infected larvae

Multi-host bacteria must rapidly adapt to drastic environmental changes, relying on integration of multiple stimuli for an optimal genetic response. Erwinia spp. are phytopathogens that cause soft-rot disease in plants. Erwinia carotovora Ecc15 is used as a model for bacterial oral-route infection in Drosophila melanogaster as it harbors a gene, the Erwinia virulence factor (Evf), which has been previously shown to be a major determinant for infection of D. melanogaster gut. However, the factors involved in regulation of evf expression are poorly understood. We investigated whether evf could be controlled by quorum sensing since, in the Erwinia genus, quorum sensing regulates pectolytic enzymes, the major virulence factors needed to infect plants. Here, we show that transcription of evf is positively regulated by quorum sensing in Ecc15 via the acyl-homoserine lactone (AHL) signal synthase ExpI, and the AHL receptors ExpR1 and ExpR2. Moreover, we demonstrate that the GacS/A two-component system is partially required for evf expression. We also show that the load of Ecc15 in the gut depends upon the quorum sensing-mediated regulation of evf. Furthermore, we demonstrate that larvae infected with Ecc15 suffer a developmental delay as a direct consequence of the regulation of evf via quorum sensing. Overall, our results show that Ecc15 relies on quorum sensing to control production of both pectolytic enzymes and Evf. This regulation influences the interaction of Ecc15 with its two known hosts, indicating that quorum sensing and GacS/A signaling systems may impact bacterial dissemination via insect vectors that feed on rotting plants. SignificanceIntegration of genetic networks allows bacteria to rapidly adapt to changing environments. This is particularly important in bacteria that interact with multiple hosts. Erwinia carotovora Ecc15 is a plant pathogen that uses Drosophila melanogaster as a vector. To interact with these two hosts, Ecc15 uses two different sets of virulence factors: plant cell wall-degrading enzymes to infect plants and the Erwinia virulence factor (evf) to infect Drosophila. Our work shows that, despite the virulence factors being different, both are regulated by homoserine lactone quorum sensing and the two component GacS/A system. Moreover, we show that these pathways are essential for Ecc15 loads in the gut of Drosophila and that this interaction carries a cost to the vector in the form of a developmental delay. Our findings provide evidence for the importance of quorum sensing regulation in the establishment of multi-host interactions.