Project description:The nematode Caenorhabditis elegans feeds on microbes in its natural environment. Some of these microbes are pathogenic and thus harmful to C. elegans. To minimize resulting fitness reductions, C. elegans has evolved various defence mechanisms including behavioural responses (e.g. avoidance behaviour) that reduce contact with the infectious microbes. In this study, we characterized the genetic architecture of natural variation in C. elegans avoidance behaviour against the infectious stages of the Gram-positive bacterium Bacillus thuringiensis. We performed an analysis of quantitative trait loci (QTLs) using recombinant inbred lines (RILs) and introgression lines (ILs) generated from a cross of two genetically as well as phenotypically distinct natural isolates N2 and CB4856. The analysis identified several QTLs that underlie variation in the behavioural response to pathogenic and/or non-pathogenic bacteria. One of the candidates is the npr-1 gene. This gene encodes a homolog of the mammalian neuropeptide receptor. Npr-1 was previously indicated to fully contribute to behavioural defence against the Gram-negative bacterium Pseudomonas aeruginosa and food patch-leaving behaviour on Escherichia coli. Interestingly, in our study, npr-1 is not the only gene mediating avoidance behaviour toward Bacillus thuringiensis. Moreover, our functional analyses show that npr-1 alleles appear to influence survival and avoidance behaviour toward Bacillus thuringiensis in exactly the opposite way than toward Pseudomonas aeruginosa. Our findings highlight the role of npr-1 in fine-tuning nematode behaviour in an ecological context depending on the microbe to which C. elegans is exposed. These opposite phenotypes reflect the diversity in innate immunity to pathogens. To understand the mechanism involved in these opposite phenotypes, we carried out a whole-genome transcriptomics study by RNA-Sequencing. This study includes two pathogens: Pseudomonas aeruginosa PA14 and Bacillus thuringiensis B-18247 (BT247), two strains: N2 and npr-1 (ur89), two time points (12 and 24h) and standard lab food E. coli OP50 as control. mRNA profiles of wild type (WT) and npr-1 (ur89) C.elegans exposed to either Bacillus thuringiensis B-18247, Pseudomonas aeruginosa PA14 or standard lab food E. coli OP50 at 12h or 24h were generated by deep sequencing, in double or triplicate, using Illumina HiSeq2000.

Project description:The nematode Caenorhabditis elegans feeds on microbes in its natural environment. Some of these microbes are pathogenic and thus harmful to C. elegans. To minimize resulting fitness reductions, C. elegans has evolved various defence mechanisms including behavioural responses (e.g. avoidance behaviour) that reduce contact with the infectious microbes. In this study, we characterized the genetic architecture of natural variation in C. elegans avoidance behaviour against the infectious stages of the Gram-positive bacterium Bacillus thuringiensis. We performed an analysis of quantitative trait loci (QTLs) using recombinant inbred lines (RILs) and introgression lines (ILs) generated from a cross of two genetically as well as phenotypically distinct natural isolates N2 and CB4856. The analysis identified several QTLs that underlie variation in the behavioural response to pathogenic and/or non-pathogenic bacteria. One of the candidates is the npr-1 gene. This gene encodes a homolog of the mammalian neuropeptide receptor. Npr-1 was previously indicated to fully contribute to behavioural defence against the Gram-negative bacterium Pseudomonas aeruginosa and food patch-leaving behaviour on Escherichia coli. Interestingly, in our study, npr-1 is not the only gene mediating avoidance behaviour toward Bacillus thuringiensis. Moreover, our functional analyses show that npr-1 alleles appear to influence survival and avoidance behaviour toward Bacillus thuringiensis in exactly the opposite way than toward Pseudomonas aeruginosa. Our findings highlight the role of npr-1 in fine-tuning nematode behaviour in an ecological context depending on the microbe to which C. elegans is exposed. These opposite phenotypes reflect the diversity in innate immunity to pathogens. To understand the mechanism involved in these opposite phenotypes, we carried out a whole-genome transcriptomics study by RNA-Sequencing. This study includes two pathogens: Pseudomonas aeruginosa PA14 and Bacillus thuringiensis B-18247 (BT247), two strains: N2 and npr-1 (ur89), two time points (12 and 24h) and standard lab food E. coli OP50 as control.

Project description:C. elegans has served as a laboratory model organism due to its ease of manipulation and the availability of both forward and reverse genetics. In recent years, efforts to study host-pathogen interactions in C. elegans have increased. For example, analysis of infections by bacteria such as Pseudomonas, Salmonella or Serratia has revealed the existence of innate immune pathways in C. elegans that are also conserved in vertebrates. To date, there has been no natural virus infection reported in C. elegans or C. briggsae. Here we describe evidence of natural virus infection in wild isolates of both C. elegans and C. briggsae. Two highly divergent but related RNA viruses in the family Nodaviridae, tentatively named Orsay nodavirus and Santeuil nodavirus, were detected and their genomes partially sequenced. Infected worm lysates passed through 0.2 um filters could be used to infect uninfected worms, which could be further passaged for many generations. Furthermore, the viruses were subject to processing by the RNAi machinery as evidenced by the detection of virally derived small RNAs. Infection of mutant worms defective in small RNA pathways yielded more robust levels of viral RNA as compared to infection of isogenic N2 reference worms. These data demonstrate that nodaviruses are natural parasites of nematodes in the wild. Further study of the interactions between these viruses and nematodes is likely to provide insight into the natural ecology of nematodes and may reveal novel innate immune mechanisms that respond to viral infection. Two small RNA libraries (18-30 nt) from nodavirus-infected and cured C. elegans wild isolate JU1580 were sequenced on the Illumina Genome Analyzer II platform. Samples were treated with tobacco acid pyrophosphatase to allow cloning of small RNA molecules with 5'-triphosphates. Each sample was labelled with a unique four base pair barcode and libraries were multiplexed together with a third library (not included in this submission). The multiplexed libraries were sequenced in triplicate.

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Natural C. elegans microbiota protects against infection via production of a cyclic lipopeptide of the viscosin group

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