Potential reservoir hosts of the pathogenic chytrid fungus

Background/Question/Methods

Batrachochytrium dendrobatidis (Bd) is a pathogenic chytrid fungus implicated in worldwide amphibian declines. Bd was once thought to be highly host-specific, but can in fact infect non-amphibian hosts like crayfish (Procambarus spp.). When there are multiple hosts for a pathogen, some can serve as reservoir hosts, which can profoundly affect disease dynamics by increasing pathogen persistence, virulence, and movement between host populations. Recently, it was demonstrated that Bd can infect and cause mortality in the soil nematode, Caenorhabditis elegans, but it is unclear whether C. elegans can act as a true reservoir host for the fungus in the absence of amphibian hosts. Here, we test whether C. elegans, which is syntopic with many amphibian species, are possible reservoir hosts for Bd. 

Results/Conclusions

In culture experiments, Bd was cultured in the presence and absence of C. elegans, and all plates were inoculated with E.coli as a food source for C. elegans. Bd survived in the presence of C. elegans and E.coli but did not survive when cultured with just E. coli alone. This suggests that Bd was either infecting C. elegans or surviving on C. elegans metabolites. Additionally, in preliminary experiments, nematodes were not reduced by the presence of live Bd compared to Bd-free plates. However, when nematodes were cultured with Bd metabolites alone (no live zoospores), C. elegans populations were reduced.  The most parsimonious explanation for these findings is that these two species are providing resources for one another. Bd is likely infecting C. elegans and C. elegans is likely consuming Bd zoospores. These results suggest that soil nematodes may be reservoir hosts for Bd.