Antifungal defenses in subterranean termites and Cryptocercus woodroaches
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Type of Workapplication/pdf
ix, 46 pages
DepartmentTowson University. Department of Biological Sciences
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The secreted B-1,3-glucanase activity of Gram-negative bacteria binding proteins (GNBPs) provides woodroaches with important prophylactic protection from fungal pathogens such as Metarhizium anisopliae. Cuticular washes have antifungal activity against M. anisopliae conidia that was suppressed by an inhibitor (GDL) of termite GNBP B-1,3- glucanase activity. Cryptocercus punctulatus nymphs that were treated with GDL and subsequently exposed to M. anisopliae conidia show significantly greater mortality than the untreated nymphs exposed to conidia. The B-1,3- glucanase activity of GNBPs therefore appears to be critical for protecting Cryptocercus woodroaches from fungal pathogens. Analysis of local and foreign Metarhizium strains indicates that Metarhizium has the potential to influence the evolution of the termite immune system. To investigate Metarhizium strain variety and virulence, six strains were isolated and identified from nearby Reticulitermes flavipes collection sites. Colonies varied significantly in their susceptibility to the six isolates of Metarhizium, which were collected across a rough transect of approximately 1 km. These fungal isolates represented three separate species, M. brunneum, M. robertsii and M. guizhouense. There was a significant correlation between the genetic distance between isolates and their difference in virulence in three of four termite colonies. This variety of Metarhizium over small spatial scales suggests that adaptive evolution in the termite immune system may arise as a result of a virulent Metarhizium strain periodically creating epizootics that are countered by the evolution of resistance in the host. Messenger RNA sequences of Gram Negative Bacteria-binding Protein 1 (GNBP1) were identified and analyzed in two species of subterranean termites. Using population genetic methods, comparisons were made between this gene and two additional antifungal genes in the subterranean termites and two species of woodroaches, Cryptocercus punctulatus and Cryptocercus wrighti. An analysis of nucleotide intraspecific polymorphism indicated that these genes frequently face selective sweeps, possibly as a result of a virulent fungal strain spreading through populations and selecting for resistant specific alleles that afford the greatest resistance to infection.