The p38 mitogen activated protein kinase and the insulin/IGF-1 signalling pathways. In particular the IIS pathway with the gene regulators DAF-2 and DAF-16, is increasingly recognised for its important role in stress response, aging and immune homeostasis across nematodes, insects and mammals. Furthermore, the IIS pathway is known to play a key role in the innate immune response against different pathogen-induced stresses, including colonization and bacterial virulence factors. In C. elegans the binding of insulin to DAF-2 triggers a phosphorylation cascade that results in activation of PDK-1 and eventual retention of the DAF-16 transcriptional activator in the cytoplasm. Deactivation or loss of DAF-2 function allows DAF-16 to move to the nucleus where it enhances the expression of genes including among others sod-3, spp-1 and lys-7, which are involved in detoxification, antimicrobial peptide expression and antimicrobial lysozyme production, respectively. Moreover recent data indicates that the canonical IIS signalling diverges at PDK-1 into a second arm of the pathway mediated by the protein WWP-1 . In the present study, we hypothesised that C. elegans makes use of this immune response pathway not only in the situation of infection by pathogenic organisms, but also to neutralize the effect of toxic bacterial secondary metabolites, such as SCH772984 Violacein that originate from non-pathogens. Furthermore studying the mechanisms in which C. elegans mediates resistance to bacterial metabolites may shed further light into their molecular/cellular targets. To address this hypothesis, we first confirm that violacein is responsible for the toxic activity against C. elegans in clone 20G8 and its parental strain Microbulbifer sp. D250. We further show that the expression of enzymes that synthesize violacein in E. coli facilitates bacterial accumulation in the host intestine and induces apoptosis in the nematode. Finally we demonstrate that the IIS immune pathway modulates C. elegans sensitivity to violacein toxicity, most likely via the control of genes involved in detoxification and antimicrobial production. In this study, we identified violacein as the metabolite responsible for the antinematode activity of Microbulbifer sp. D250. Violacein is arguably best known for its antibacterial properties and its activity as a potentially novel therapeutic against a range of tumors. However, to the best of our knowledge, and with the exception of studies related to cancer therapy, this is the first report of violacein toxicity towards a multicellular eukaryote, thus adding to the list of biological functions for this natural metabolite. Genetic analysis identified an operon of five conserved biosynthesis genes vioA-E that have been identified across all violacein-producing strains studied to date. Interestingly, mutations in vioC or vioD result in a grey colony pigmentation, reminiscent of the accumulation of the violacein precursor pro-violacein. Pro-violacein differs from violacein by the absence of one oxo-group in the C15 position. This minor chemical difference, however, has a substantial impact on the toxicity, as the grey-pigmented vioC mutant did not kill nematodes in our study.