Project description: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.
Project description:A fliZ mutant in the entomopathogenic bacterium X. nematophila is attenuated in virulence in the insect. The goal of this study is to compare transcriptomes of the fliZ mutant and wild type strain to identify the FliZ regulon.
Project description:A fliZ mutant in the entomopathogenic bacterium X. nematophila is attenuated in virulence in the insect. The goal of this study is to compare transcriptomes of the fliZ mutant and wild type strain to identify the FliZ regulon. Two biological replicates of total RNA from exponential cultures of WT strain and fliZ mutant were analysed by deep sequencing, using Illumina HiSeq 2000.
Project description:The CpxRA signal transduction system, which in Escherichia coli regulates surface structure assembly and envelope maintenance, is involved in the pathogenic and mutualistic interactions of the entomopathogenic bacterium Xenorhabdus nematophila. When DeltacpxR1 cells were injected into Manduca sexta insects, the time required to kill 50% of the insects was twofold longer than the time observed for wild-type cells and the DeltacpxR1 cells ultimately killed 16% fewer insects than wild-type cells killed. During mutualistic colonization of Steinernema carpocapsae nematodes, the DeltacpxR1 mutant achieved colonization levels that were only 38% of the wild-type levels. DeltacpxR1 cells exhibited an extended lag phase when they were grown in liquid LB or hemolymph, formed irregular colonies on solid medium, and had a filamentous cell morphology. A mutant with a cpxRp-lacZ fusion had peaks of expression in the log and stationary phases that were conversely influenced by CpxR; the DeltacpxR1 mutant produced 130 and 17% of the wild-type beta-galactosidase activity in the log and stationary phases, respectively. CpxR positively influences motility and secreted lipase activity, as well as transcription of genes necessary for mutualistic colonization of nematodes. CpxR negatively influences the production of secreted hemolysin, protease, and antibiotic activities, as well as the expression of mrxA, encoding the pilin subunit. Thus, X. nematophila CpxRA controls expression of envelope-localized and secreted products, and its activity is necessary for both mutualistic and pathogenic functions.
Project description:Photorhabdus luminescens bacteria alternate lifestyles between its pathogenic insect host and its mutualistic nematode host. We found that Photorhabdus changes radically from the insect pathogenic form (P-form) to slow growing small cells when initiating mutualism (M-form). Here we characterize the gene expression of the M-form relative to the P-form.