Olivier Zugasti et al. (2007) International Worm Meeting "Emerging complexity of anti-fungal defences in C. elegans."

Hinrich Schulenberg, Nathalie Pujol, Jonathan Ewbank, Olivier Zugasti

[International Worm Meeting, 2007]

Infection of worms by the fungus Drechmeria coniospora leads to an innate immune reaction involving the rapid up-regulation of members of the nlp and cnc/caenacin gene families that encode antimicrobial peptides (AMPs). We previously reported that the expression upon infection of one of these peptides, NLP-29, requires TIR-1, a homologue of SARM, a Toll/interleukin 1 receptor (TIR)-domain protein (1) that acts upstream of a NSY1/SEK-1/PMK-1 p38 MAPK signalling pathway in bacterial resistance and neuronal development (2, 3). Many of the infection-inducible nlp and cnc genes are found in two distinct genomic clusters on the left arm of chromosome V. Phylogenetic analysis revealed that these AMPs form an exclusive monophylic group separated from the other nlp genes. Within this monophylum, almost all the cnc genes cluster together. Furthermore, the genes nlp-27 to nlp-31 form a well-supported clade. Searches in available genomic sequence of related nematodes C. briggsae and C. remanei reveal that AMP genes of the nlp-29 cluster specifically expanded in C. elegans and are evolving under positive selection. Strikingly, we show that all members of this cluster are up-regulated by infection in a p38-dependent manner, but differ in their response to wounding and osmotic stress. For example, unlike nlp-29 (see abstract by Pujol et al.), nlp-30 is upregulated by infection and wounding, but not under high salt conditions. In clear contrast to nlp-29 and nlp-30, cnc-2 is neither induced by wounding nor osmotic stress. Moreover, the induction of cnc-2 seen upon fungal infection is independent of a p38 signalling pathway but appears to involve an uncharacterised non-canonical TGF-<font face=symbol>b</font> pathway as it requires SMA-6, but not the known SMAD complex. Although daf-2 mutants are more resistant to Drechmeria infection, unexpectedly, the expression of both nlp-29 and cnc-2 is abrogated in a daf-2 mutant, in a daf-16-dependent fashion. Thus distinct stimuli, including infection, osmotic stress and wounding, induce the up-regulation of different AMPs using genetically separable signalling pathways. These results bring to light an unexpected complexity of AMP gene regulation in C. elegans. 1. Couillault et al (2004) Nat Immunol 5, 488-494. 2. Chuang, & Bargmann (2005) Genes Dev 19, 270-81. 3. Liberati et al (2004) Proc Natl Acad Sci U S A 101, 6593-8.

Viktoria Wegewitz et al. (2006) European Worm Meeting "Are Males Important? An Experimental Approach"

Hinrich Schulenburg, Viktoria Wegewitz, Adrian Streit

[European Worm Meeting, 2006]

Are Males Important? An Experimental Approach. Viktoria Wegewitz1, Hinrich Schulenburg2 and Adrian Streit1. One proposed advantage of outcrossing is creating new favourable gene combinations by recombination, which possibly helps adaptation to changing environmental conditions. This model predicts two alternative strategies for reproduction in Caenorhabditis elegans: Selfing would be an advantage under constant conditions because favourable combinations of genes are preserved and the cost of male production is reduced. In contrast outcrossing would be an advantage under changing environmental conditions. If this hypothesis is true and there are genetic determinants for the abundance of males, constant conditions should select for low incidence of males and changing selective pressure for higher number of males. We plan to test this model in the following way: A genetically variable population with a high number of males will be produced by interbreeding the two wild type strains N2 and CB4856. Half of this population will be cultivated under changing selection pressure of different pathogenic bacteria. The other half of the population will be kept under standard laboratory conditions. We have already shown that in N2 and CB4856 males are maintained at different rates in growing cultures under standard laboratory conditions. While N2 males are lost from the population within a few generations, CB4856 males are maintained at significantly higher proportion over longer periods, especially in large populations. This indicates that male abundance is, at least in part, determined genetically and that the corresponding genetic component differs between N2 and CB4856. If the model outlined above is true, we expect that the populations from the two treatments in our selection experiment differ in male frequency. We are also testing parameters that might be the reason for the different maintenance of males, for example mating efficiency and brood size. First Results will be presented.

Radeke, Leah et al. (2021) International Worm Meeting "Genomic analysis of natural Stenotrophomonas bacteria and their effects on wild and domesticated C. elegans"

Radeke, Leah, Herr, Joshua, Herman, Michael

[International Worm Meeting, 2021]

Natural isolates of Caenorhabditis elegans are found in rotting vegetation in association with a multitude of bacteria (Dirksen et al., 2016). Interestingly, the microbiomes of nematodes isolated from different substrates appear to harbor a common set of bacterial genera (Zhang et al., 2017). Among these are members of the Stenotrophomonas genus. While not specifically identified yet as a component of the C. elegans microbiome, certain strains of Stenotrophomonas maltophilia have been shown to reduce C. elegans survivorship and evade host defense responses (White et al., 2016, Radeke and Herman, 2020). We have found that S. maltophilia strains are differentially virulent to C. elegans and show both common and strain-specific transcriptomic responses (White et al., 2018, Radeke and Herman, 2020). In addition, comparison of S. maltophilia genomes revealed that most S. maltophiliagenes are strain-specific, suggesting that many potential virulence factors are unique. In order to determine whether these observations reflect natural interactions, we explored the interactions between three natural C. elegans strains and 12 Stenotrophomonas sp. previously isolated from the C. elegans microbiomes of each strain or surrounding environment (obtained from the Felix, Samuel and Schulenberg laboratories). Survivorship analysis and brood counts, used as a measure of fitness, revealed that these natural Stenotrophomonas isolates showed variations in virulence and fecundity to the C. elegans natural strains and N2. Moreover, we found variation in survival and fecundity between each natural nematode strain and N2 in response to certain Stenotrophomonas isolates. This suggests differential adaptation of the C. elegans strains to natural Stenotrophomonas isolates. We determined the genome sequences of all 12 Stenotrophomonas strains to discover whether differences in observed pathogenicity between strains can be explained by differences in genetic features. Our phylogenetic analysis includes these, and 142 genomes that represent all identified lineages of Stenotrophomonas. We are testing for the presence of 48 genes previously characterized as virulence genes in other systems and testing whether our C. elegans life history data can aid in finding others. Further analyses of the bacterial genomic differences coupled with genome comparison of the nematode strains could help to understand effects of local adaptation to organismal-microbiome interactions.