Disease-decreasing diversity: more biodiverse C. elegans communities contain fewer nematode-infecting pathogens

Natural populations of Caenorhabditis elegans contain many co-occurring nematodes and also pathogens that infect them, such as oomycetes, microsporidia and viruses. 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 mechanism is unidentified for microscopic species. Here, we unraveled wild C. elegans communities to investigate the effect of nematode biodiversity on the prevalence of nematode-infecting pathogens. Natural nematode communities including C. elegans were collected from decaying plant substrates. Next, nematodes in these communities were fully characterized, mostly to species-level resolution, after the nearly complete eukaryotic SSU was PCR-amplified and sequenced by Nanopore sequencing. Using (wild) C. elegans as a target species, we could use fluorescent reporter strains to identify bacterial, microsporidian and viral pathogens present, including potentially novel species. Together, our data indicates that communities rich in nematode species contained fewer specialist pathogens than those with low nematode biodiversity. Future work will use collected C. elegans and other nematode species for multispecies infection experiments to establish which factors drive the ‘dilution effect of disease’.