Project description:Photorhabdus luminescens lives in a mutualistic association with entomopathogenic nematodes and is pathogenic for insects. Variants of Photorhabdus frequently arise. VAR* is a colonial and phenotypic variant displaying delayed pathogenicity in the insect, Spodoptera littoralis. In this study, we evaluated the role of transcriptomic modulation in determining the phenotypic variation and delayed pathogenicity of VAR* with respect to the corresponding wild-type form, TT01alpha. A P. luminescens microarray was used to determine changes in transcript profiles in the exponential and stationary phase growth phase of VAR* and TT01alpha grown in LB broth.
Project description:Secretion systems are used as weapons by a variety of Gram-negative bacteria. Among them the Type VI Secretion System (T6SS) gained more interest throughout the last years. The system functions as a molecular nano-weapon: it is used in inter-kingdom competition by various bacteria to deliver toxic effectors in target cells. Here we describe the role of the T6SS in Photorhabdus laumondii subsp. laumondii strain DJC, an entomopathogenic biocontrol agent able to live in different environmental niches, such as in symbiosis with nematodes and in the rhizosphere on plant roots. Using bioinformatic and protein motif analyses we identified four T6SS gene clusters (T6SS-1, T6SS-2, T6SS-3 and T6SS-4) and multiple orphan T6SS related genes in the genome of P. laumondii. Furthermore, we highlighted 11 T6SS effector-immunity pairs, including three undescribed membrane disrupting effectors, each with putatively different antibacterial activities. By label-free mass spectrometry of P. laumondii wild type cells and respective T6SS-deficient strains, we could point out a cross-link between T6SS and other Photorhabdus’ virulence related mechanisms such as PVCs, T3SS and pyocins. Furthermore, a change in motility as well as in the secondary metabolism was observed upon T6SS-deficiency. Here, we shed light on the T6SS in P. laumondii DJC and suggesting a cross-link of various virulence mechanisms, which could help to gain knowledge on T6SS and better figure out the Photorhabdus ability to live in polymicrobial environments.
Project description:Rapid modulation of gene expression is a key feature for the success of bacteria, particularly for those that rapidly have to adapt to different niches. The lifecycles of Photorhabdus and Xenorhabdus involve a mutualistic association with nematodes as well as an entomopathogenic phase1,2, both of which rely on the production of numerous specialized metabolites (SMs) 3,4. Several regulators have been previously implicated in the regulation of SM production in these genera3,4. However, the molecular underpinnings regulating SM production and the role of small regulatory RNAs (sRNAs) in this process are unknown. Here we describe the mechanism underlying RNA-mediated control of SM synthesis. We show that the Hfq-dependent sRNA, ArcZ, is an essential requirement for SM production. We discovered that ArcZ directly base-pairs with the mRNA encoding HexA, a key repressor of SM genes. We further demonstrate that the ArcZ regulon is not restricted to SM production, but rather modulates up to ~15% of the transcriptional output in both Photorhabdus and Xenorhabdus. Together, our study shows that sRNAs are crucial for SM production in these species, reveals previously unknown targets for biosynthetic pathway manipulations, and offers a new tool for the (over)production, isolation and identification of unknown natural products.
Project description:Dam, the most described bacterial DNA-methyltransferase, is widespread in gamma-proteobacteria. Dam DNA methylation can play a role in various genes expression and is involved in pathogenicity of several bacterial species. In the entomopathogenic bacterium Photorhabdus luminescens, a dam ortholog was identified. Overexpression of dam in P. luminescens did not impair growth ability in vitro. In contrast, compared to a control strain harboring an empty plasmid, a significant decrease in motility was observed in the dam-overexpressing strain. In addition, the dam-overexpressing P. luminescens strain showed a delayed virulence compared to that of the control strain after injection in larvae of the lepidopteran Spodoptera littoralis. These results reveal that Dam plays a major role during P. luminescens insect infection.
Project description:UPLC-HRMS Screen of 30 entomopathogenic bacterial strains of the genera Xenorhabdus and Photorhabdus. For further details please have a look on attached publication.
Project description:Photorhabdus luminescens lives in a mutualistic association with entomopathogenic nematodes and is pathogenic for insects. Variants of Photorhabdus frequently arise. VAR* is a colonial and phenotypic variant displaying delayed pathogenicity in the insect, Spodoptera littoralis. In this study, we evaluated the role of transcriptomic modulation in determining the phenotypic variation and delayed pathogenicity of VAR* with respect to the corresponding wild-type form, TT01alpha. A P. luminescens microarray was used to determine changes in transcript profiles in the exponential and stationary phase growth phase of VAR* and TT01alpha grown in LB broth. Direct transcriptomic comparisons were carried out between VAR* and TT01alpha grown in LB broth. RNA were extracted from bacterial cells in the exponential growth phase (6-hour-old culture, 5 x 107 cfu/ml) and stationary phase (45-hour-old culture, 5 x 108 cfu/ml). Each microarray comparison (TT01alpha versus VAR* growth in exponential growth or stationary phase) included six slides, with three dye-swapping replicates. Each microarray comparison is done twice with two independant biological extractions (repbiol1 or 2).
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.