Bacterial Genetic Approach to the Study of Reactive Oxygen Species Production in During Infection.

Over the last decade, an increasing number of reports presented larvae as an important model to study host-pathogen interactions. Coherently, increasing information became available about molecular mechanisms used by this host to cope with microbial infections but few of them dealt with oxidative stress. In this work, we addressed the role of reactive oxygen species (ROS) produced by the immune system of to resist against , an intracellular pathogen responsible for a wide range of infections. We confirmed that was pathogen for and showed that it had to reach a minimal bacterial load within the hemolymph to kill the larvae. ROS production by was revealed by the virulence defects of mutants lacking catalases/peroxiredoxins or cytoplasmic superoxide dismutases, both strains being highly sensitive to these oxidants. Finally, we used bacterial transcriptional fusions to demonstrate that hydrogen peroxide (HO) was produced in the hemolymph of during infection and sensed by . In line with this observation, the HO-dependent regulator OxyR was found to be required for bacterial virulence in the larvae. These results led us to conclude that ROS production is an important mechanism used by to counteract bacterial infections and validate this host as a relevant model to study host-pathogen interactions.