The OxyR regulon in the entomopathogenic bacterium Xenorhabdus
Xenorhabdus nematophila is a Gram-negative bacterium, mutually associated with the soil nematode Steinernema carpocapsae and this nematobacterial complex is parasitic for a broad spectrum of insects. The transcriptional regulator OxyR is widely conserved in bacteria, but the OxyR regulon can vary significantly between species. OxyR activates the transcription of a set of genes that influence cellular defense 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 nematobacterial complexes harboring the oxyR mutant symbiont were able to rapidly kill the insect larvae in less than 48h 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 significant increased number of offspring of the nematobacterial 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. Overall design: Three independent RNA samples, each corresponding to a pool of total RNA extracted independently from 3 biological replicates cultures of: F1 WT grown in LB  or LB supplemented with paraquat (10mM) (=oxydative stress) harvested in exponential phase (OD= 0.3) OxyR mutant grown in LB or LB supplemented with paraquat (10mM) (=oxydative stress) harvested in exponential phase (OD= 0.3) Deep sequencing, performed using Illumina HiSeq 2000