Abstract
The Gram-negative bacterium Photorhabdus luminescens which symbiotically associates with the entomopathogenic nematode Heterorhabditis bacteriophora, has a broad insecticidal and nematicidal activity. The virulence of P. luminescens toward the non-mutualistic nematode Caenorhabditis elegans has not been described. We showed that when fed on P. luminescens, the intestinal cells of C. elegans worms become delicate and some crystal-like structure was developed within the intestinal lumen. Next, we examined the requirement of the p38 mitogen-activated protein kinase (MAPK) and insulin/IGF-1 signaling pathway against P. luminescens. Depletion of pmk-1 by RNAi enhances susceptibility to P. luminescens, and numerous downstream targets regulated by the p38 MAPK pathway were induced when fed on P. luminescens. On the other hand, knockdown of daf-16 has no effects on C. elegans lifespan, but knockdown of daf-2 dramatically increased resistance to P. luminescens in a daf-16-dependent manner. We also revealed one of the daf-2 ligands ins-7 was induced and ins-7 deletion mutant survived longer when fed on P. luminescens. These results suggest the p38 MAPK pathway is activated and required for the host defense against P. luminescens. Insulin/IGF-1 signaling pathway is inactivated by P. luminescens through the overexpression of insulin-like gene.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-3-274) contains supplementary material, which is available to authorized users.
Highlights
Photorhabdus luminescens is an enteric Gram-negative bacterium which can be a pathogen producing a broadspectrum toxins with antibacterial, antifungal insecticidal, and nematicidal activities, or a symbiont of the entomopathogenic nematode (EPN) Heterorhabditis bacteriophora orchestrating insect pathogenicity (Waterfield et al 2009)
P. luminescens TT01 causes drastic damage to C. elegans intestine C. elegans can be infected by many other bacterial strains (Couillault and Ewbank 2002; Sicard et al 2007; Engelmann et al 2011; Fischer et al 2012, 2013; Julien-Gau et al 2014)
We showed that P. luminescens TT01 was highly pathogenic to C. elegans
Summary
Photorhabdus luminescens is an enteric Gram-negative bacterium which can be a pathogen producing a broadspectrum toxins with antibacterial, antifungal insecticidal, and nematicidal activities, or a symbiont of the entomopathogenic nematode (EPN) Heterorhabditis bacteriophora orchestrating insect pathogenicity (Waterfield et al 2009). Several toxin proteins produced by P. luminescens and other pathogenic bacteria have been identified, e.g. the toxin complex (Tc), the “Makes caterpillars floppy” (Mcf ), Photox, and Photorhabdus insect related (Pir) toxins (Bowen et al 1998; Daborn et al 2002; Duchaud et al 2003; Visschedyk et al 2010). Even though the pathogenicity of several P. luminescens toxins is under active investigation (Dowling et al 2004, 2007; ffrenchConstant et al 2007; Vlisidou et al 2009; Lang et al 2010, 2011, 2013; Gatsogiannis et al 2013; Yang and Waterfield 2013) and the genome data of P. luminescens are available (Duchaud et al 2003), the underlying mechanism of their virulence remains unclear
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