Antimicrobial activity of actinobacteria isolated from the guts of subterranean termites

Subterranean termites live in an environment in which they are constantly exposed to potentially pathogenic microorganisms. Healthy termite colonies, however, generally show remarkably low growth of fungi and bacteria. In this study, we examined the potential role of actinobacteria isolated from the gut of various Reticulitermes spp. in controlling these microorganisms.  A total of 57 actinobacteria strains were isolated on selective chitin media and tested for inhibitory activity toward both bacteria and fungi by agar plate assay. Inhibition of basidiomycete, wood-rot fungi was also examined as these fungi may be competitors for resources in a termite environment. Test microorganisms included two brown-rot fungi, two white-rot fungi, two opportunistic termite pathogens Serratia marsescens, Metarhizium anisopliae and the saprophytic fungus, Trichoderma sp.  A number of additional microbial pathogens were also evaluated to further characterize antimicrobial activity of the actinobacteria isolates. Overall, the majority of actinobacteria isolated showed activity against one or more test microorganisms. Some actinobacteria exhibited broad inhibitory activity, while others were inhibitory to only one organism or group of organisms. This in vitro antimicrobial activity of termite-associated actinobacteria suggest a potentially ecologically relevant role in the termite colony, suggesting that further work on the role of these organisms in maintaining termite health and nest hygiene is warranted.