Worms About Town: a citizen science project discovers microsporidian parasites of nematodes through environmental sampling.

Microsporidia are a diverse group of fungal parasites that infect humans and agriculturally important animals. Caenorhabditis elegans has emerged as a powerful host for investigating microsporidian biology, yet how ecological factors such as geography, seasonality, temporality, and sample substrate impact infection of C. elegans and other nematodes remains unclear. To address this, we developed a citizen scientist network, Worms About Town, to annually survey wild nematodes for microsporidia across Toronto, Canada. Here, we describe results from the first year (2024) of the project. One hundred twenty-seven environmental samples from various plant substrates were collected, 60 of which contained wild nematodes and four of which were infected with microsporidia. Two isolates of Nematocida homosporus, a known generalist microsporidian of nematodes, were identified. The other two microsporidia isolates belong to undescribed species of Pancytospora and Enteropsectra, genera distantly related to human-infecting microsporidia. Three nematode isolates of the Caenorhabditis genus were discovered, including two isolates of C. elegans, a species not previously reported in Ontario. Both N. homosporus isolates were found in C. elegans, and one can infect a laboratory strain of C. elegans. Our study expands knowledge of natural nematode-microsporidia diversity and provides a framework for systematically investigating how ecological factors shape this host-parasite system.