Pathogen-specific immune responses from symbionts in a subterranean termite, Reticulitermes flavipes (Kollar)

Living eusocially in a microbe-rich habitat puts subterranean termite colonies at risk for pathogen outbreaks. Termites have evolved multiple mechanisms to combat potential infections including hygienic behaviors and innate immunity. Recent work in lower termites has highlighted a role for more ‘stereotypical’ responses, as well as for protist symbionts in defense against fungal pathogens. In bioassays, we determined that Reticulitermes flavipes workers with reduced microbiota were 2-3X more susceptible to fungal pathogens (Beauveria bassiana and Metarhizium anisopliae) but were no more prone to bacterial infection (Serratia marcescens) than control groups. For this study, we hypothesized that protist-derived, glycosyl hydrolase family 7 (GHF7) enzymes play a role in R. flavipes immunity via β-1, 3-glucanase activity. To test this hypothesis, we characterized the enzyme activity of two GHF7s with potential for β-1, 3-glucanase activity using a variety of substrates. Next, spores from B. bassiana and M. anisopliae were incubated with recombinant GHF7s and this treatment resulted in reduced fungal germination. These findings emphasize the intimate relationship that exists between R. flavipes workers and their symbiota and suggest that protist GHF7s may be an important mechanism for symbiont-mediated immunity against fungal pathogens.