Symbiont-mediated immunocomptence in the dampwood termite (Zootermopsis angusticollis)

Termites have a long co-evolutionary history with prokaryotic and/or eukaryotic gut microbes. The interaction with the eukaryotic protozoa has been historically considered critical in the nutritional welfare of lower termites. We hypothesized that, in addition to their nutritional role, hindgut symbionts may provide some benefit to their hosts immunologically. Specifically, we propose that the presence of flagellated protozoa in the hindgut of termites have antifungal properties. A series of experiments conducted on the dampwood termite Zootermopsis angusticollis tested whether gut extracts of faunated and defaunated individuals influence viability of Metarhizium anisopliae conidia to the same extent. Nymphs were defaunated by exposing them to pressurized oxygen, which eliminates the protozoa community while still retaining most of the bacterial symbionts. Extracts of guts from defaunated insects were incubated with fungal conidia and colony forming units (CFUs) were quantified and compared to those conidia incubated with extracts of faunated control (pressurized only) counterparts. Our results indicate that conidia viability is significantly reduced when incubated with extracts of faunated guts than when incubated with extracts of defaunated nestmates. In vivo studies testing the effect of gut protozoa on the susceptibility to fungal infection are underway. We predict that defaunated termites should be more susceptible to mycosis than faunated control nestmates. These data would support the hypothesis that gut symbionts of termites play a role in the host’s immunocompetence.