Novel infection by Mucor hiemalis kills Caenorhabditis hosts through intestinal perforation

The nematode Caenorhabditis elegans has emerged as a popular model system to investigate cell biology and host-pathogen interactions. Presently, C. elegans is studied as a natural host of intracellular pathogens such as microsporidia and Orsay virus along with extracellular bacterial and fungal pathogens. The use of C. elegans as a model in host-pathogen research is limited by the number of naturally occurring pathogens to the organism. Through a sampling project to identify new pathogens of C. elegans, we identified the fungus Mucor hiemalis as a pathogen of Caenorhabditis species. We observed the fungus in the intestinal lumen of wild-caught Caenorhabditis briggsae, and co-culturing the wild-caught species with infection reporter C. elegans confirmed infection by M. hiemalis. This study characterizes the fungal infection by M. hiemalis in Caenorhabditis nematodes. Fluorescence microscopy with fungal staining revealed the life cycle of M. hiemalis within multiple Caenorhabditis species at varying growth stages. We observed the killing of nematodes by M. hiemalis via intestinal perforation and assessed its host range through a series of lifespan assays. We investigated the food preference of C. elegans and determined that nematodes show a preference towards food that contains M. hiemalis spores. Lastly, we evaluated common C. elegans transcriptional immune responses and found that M. hiemalis does not induce genes associated with the intracellular pathogen response or other responses seen with previously studied bacterial and fungal pathogens. Characterization of this fungal infection in Caenorhabditis nematodes will provide new insights into the biology of pathogenic fungi and host immune responses.