Antimicrobial Activity of Actinobacteria Isolated From the Guts of Subterranean Termites.

Subterranean termites need to minimize potentially pathogenic and competitive fungi in their environment in order to maintain colony health. We examined the ability of Actinobacteria isolated from termite guts in suppressing microorganisms commonly encountered in a subterranean environment. Guts from two subterranean termite species, Reticulitermes flavipes (Kollar) and Reticulitermes tibialis Banks, were extracted and plated on selective chitin media. A total of 38 Actinobacteria isolates were selected for in vitro growth inhibition assays. Target microbes included three strains of Serratia marcescens Bizio, two mold fungi (Trichoderma sp. and Metarhizium sp.), a yeast fungus (Candida albicans (C.P. Robin) Berkhout), and four basidiomycete fungi (Gloeophyllum trabeum (Persoon) Murrill, Tyromyces palustris (Berkeley & M.A. Curtis) Murrill, Irpex lacteus (Fries) Fries, and Trametes versicolor (L.) Lloyd). Results showed both broad and narrow ranges of antimicrobial activity against the mold fungi, yeast fungus, and S. marcescens isolates by the Actinobacteria selected. This suggests that termite gut-associated Actinobacteria produce secondary antimicrobial compounds that may be important for pathogen inhibition in termites. Basidiomycete fungi were strongly inhibited by the selected Actinobacteria isolates, with G. trabeum and T. versicolor being most inhibited, followed by I. lacteus and T. palustris The degree of inhibition was correlated with shifts in pH caused by the Actinobacteria. Nearly all Actinobacteria isolates raised pH of the growth medium to basic levels (i.e. pH ∼8.0-9.5). We summarize antimicrobial activity of these termite gut-associated Actinobacteria and examine the implications of these pH shifts.

Genetic Analysis of Termite Colonies in Wisconsin.

The objective of this study was to document current areas of subterranean termite activity in Wisconsin and to evaluate genetic characteristics of these northern, peripheral colonies. Here, amplified fragment-length polymorphism was used to characterize levels of inbreeding, expected heterozygosity, and percent polymorphism within colonies as well as genetic structure among populations sampled. Genetic analysis revealed two species of termites occur in Wisconsin, Reticulitermes flavipes (Kollar) and Reticulitermes tibialis Banks, both found in the southern half of the state. Colonies of both species in Wisconsin are thought to represent the northern boundary of their current distributions. Measurements of within colony genetic variation showed the proportion of polymorphic loci to be between 52.9-63.9% and expected heterozygosity to range from 0.122-0.189. Consistent with geographical isolation, strong intercolony genetic differences were observed, with over 50% of FST values above 0.25 and the remaining showing moderate levels of genetic differentiation. Combined with low levels of inbreeding in most collection locations (FIS 0.042-0.123), we hypothesize termites were introduced numerous times in the state, likely by anthropogenic means. We discuss the potential effects of these genetic characteristics on successful colony establishment of termites along the northern boundary compared with termites in the core region of their distribution.