Relationship between virulence and enzymatic profiles in the cuticle of Tenebrio molitor by 2-deoxy-d-glucose-resistant mutants of Beauveria bassiana (Bals.) Vuill

摘要

The secretion of hydrolases by Beauveria bassiana is a main factor in the degradation of cuticle, while in filamentous fungi the resistance to 2-deoxy-d-glucose (2DG) is related to enzymatic deregulation. A series of 2DG-resistant B. bassiana strains were classified according to the phenotypes of germination (G) and radial growth rate (U_r), in addition to their virulence parameters on Tenebrio molitor. This analysis allowed distinction between mutants with greater (881.2) and lesser (884.5) G and U_r values, relative to the wild-type strain (88), which correlated with virulence parameters including maximal mortality (M) and time to reach 50% mortality (LT₅₀). Subsequently, using the cuticle of T. molitor as the substrate for these strains, an enzymatic analysis (total proteases, Pr1, chitinases and β-N-acetylglucosaminidase) showed that the contrasting virulence traits were associated with different deregulation patterns: higher specific activities (up to 100%) for the more virulent mutant 881.2 and lower enzymatic levels for mutant 884.5, specifically chitinases (33% reduction), relative to the wild-type strain (88) for both mutants. The differences in cuticle-degrading enzymes were consistent with the appearance of hyphal bodies within infected insects. This is the first study describing the altered enzymatic profiles in 2DG-resistant mutants of B. bassiana with practical implications in the selection of improved strains for biological control.