Linking biodiversity and pathogen abundance in natural nematode populations

Natural nematode populations harbor a broad range of pathogens that infect them, such as oomycetes, microsporidia and viruses. These pathogens shape nematode communities and may prove beneficial in situations where parasitic nematodes are controlled by their natural enemies and explain phenomena of suppressive soils. In macroscopic species, differences in pathogen susceptibility of hosts contribute to the ‘dilution effect’ where higher host biodiversity contributes to lower pathogen prevalence, but this effect is unidentified for microscopic species. Here, we investigated the effect of nematode biodiversity on the prevalence of nematode-infecting pathogens. Therefore, nematode populations were collected from decaying plant substrates in habitats where the model nematode species Caenorhabditis elegans was previously identified. Using (wild) C. elegans as a target species, we could use fluorescent reporter strains to physically identify bacterial, microsporidian and viral pathogens. To compare pathogen prevalence with nematode biodiversity, nematodes were counted and the number of species present was identified. Current work involves amplicon sequencing of the DNA that was collected from the wild populations to identify additional pathogens and characterize nematode species present. For nematode community characterization, nearly the complete eukaryotic SSU is amplified using PCR and sequenced by Nanopore sequencing. Moreover, many of the obtained (bacterivorous) nematodes and their pathogens have been maintained in the lab since field collection. Future work involves using this nematode-pathogen library for multispecies infection experiments comparing and testing correlations found in the field.