# OxyR is required for oxidative stress resistance of the entomopathogenic bacterium Xenorhabdus nematophila and has a minor role during the bacterial interaction with its hosts

## TL;DR

This study shows that OxyR helps the bacterium Xenorhabdus nematophila resist oxidative stress and plays a minor role in its interaction with host nematodes and insect larvae.

## Contribution

The study identifies the OxyR regulon in Xenorhabdus nematophila and its role in oxidative stress resistance and symbiotic interactions.

## Key findings

- OxyR is crucial for in vitro oxidative stress resistance in Xenorhabdus nematophila.
- An oxyR mutant showed no significant defect in reassociating with its nematode partner.
- The oxyR mutant produced more offspring in the nemato-bacterial complex compared to the wild-type strain.

## Abstract

Xenorhabdus nematophila is a Gram-negative bacterium, mutualistically associated with the soil nematode Steinernema carpocapsae, and this nemato-bacterial complex is parasitic for a broad spectrum of insects. The transcriptional regulator OxyR is widely conserved in bacteria and activates the transcription of a set of genes that influence cellular defence against oxidative stress. It is also involved in the virulence of several bacterial pathogens. The aim of this study was to identify the X. nematophila OxyR regulon and investigate its role in the bacterial life cycle. An oxyR mutant was constructed in X. nematophila and phenotypically characterized in vitro and in vivo after reassociation with its nematode partner. OxyR plays a major role during the X. nematophila resistance to oxidative stress in vitro. Transcriptome analysis allowed the identification of 59 genes differentially regulated in the oxyR mutant compared to the parental strain. In vivo, the oxyR mutant was able to reassociate with the nematode as efficiently as the control strain. These nemato-bacterial complexes harbouring the oxyR mutant symbiont were able to rapidly kill the insect larvae in less than 48 h after infestation, suggesting that factors other than OxyR could also allow X. nematophila to cope with oxidative stress encountered during this phase of infection in insect. The significantly increased number of offspring of the nemato-bacterial complex when reassociated with the X. nematophila oxyR mutant compared to the control strain revealed a potential role of OxyR during this symbiotic stage of the bacterial life cycle.