The study published in the journal mBio, from American Society for Microbiology, reveals that the bacterium Erwinia carotovora uses a quorum sensing mechanism both to activate the degradation of plant tissues and colonize the gut of the vector insect. This discovery is particularly relevant to understand the strategies employed by bacteria during the transmission between hosts in the context of vector-borne diseases.

Many insects contribute to the spread of pathogenic microorganisms among different hosts. Bacteria from the genus Erwinia, in particular, depend on insects to spread between plants and cause the soft rot disease (characterized by the softening/rotting of the plant tissues), which affects many crops around the world. The bacterium Erwinia carotovora interacts with each of its hosts through the production of different factors. When infecting plants, like the potato plant, produces proteins that degrade the stiff cell wall, softening the tissues and allowing their invasion. On the other hand, when infecting one of its vectors, the fly Drosophila melanogaster, triggers the expression of virulence factors that allow the transient colonization of the gut. Previous studies showed that, during plant infection, this bacterium monitors its cell density and activates the expression of proteins that soften the tissues in response to quorum sensing. Quorum sensing is a specific type of cell communication, used to synchronize gene expression in bacterial populations according to their cell density. 

Given the importance of quorum sensing for the interaction of the bacterium Erwinia carotovora with plants, researchers from Instituto Gulbenkian de Ciência (IGC) aimed at understanding if it was also crucial for the interaction with the insect vector Drosophila melanogaster. “We found that the strategies employed by this bacterium to infect its vector are activated according to the population density in response to the molecules of quorum sensing. Like this, the expression of the necessary factors for the interaction with the vector are independent of its presence, suggesting an anticipatory strategy that should favour a stronger interaction between the bacterium and the vector”, explains Filipe Vieira, main author of the study.

“Despite the need of different factors for this bacterium to interact with each host, we saw that when it reaches its quorum in the plant, both the plant and insect virulence factors are activated even in the absence of the insect. We think that this kind of simultaneous regulation is important for the transmission between different hosts”, explains Karina Xavier, IGC principal investigator and head of the team that conducted this research. Luís Teixeira, co-author of the study, adds that “this might be a mechanism that allows bacteria to anticipate and prepare to infect insects that are attracted by the rotting tissues of the plants.”

This study highlights the idea that, throughout evolution, organisms can reuse the same regulation pathways to activate new functions, used in different contexts, like the example of this bacterium and its ability to infect different hosts. A better understanding of the genetic regulation behind these phenomena can reveal a lot more similarities and propel new global strategies to prevent vector-borne diseases.