Integration of Escherichia coli thioredoxin (trxA) into Beauveria bassiana enhances the fungal tolerance to the stresses of oxidation, heat and UV-B irradiation

Aerial conidia from solid cultures of entomopathogenic fungi, such as Beauveria bassiana, are used as the active ingredients of most mycoinsecticides. Thus, conidial resistance to the outdoor heat and UV stresses is of special merit for the field persistence and efficacy of a fungal formulation against arthropod pests. To enhance fungal resistance to the stresses, Escherichia coli thioredoxin (trxA) enabling to maintain intracellular redox homeostasis was integrated into a wild-type strain of B. bassiana. The heterologous trxA expressed in three transgenic strains increased the conidial antioxidant capability by 18-20% in comparison with the wild-type strain. Consequently, their thermotolerance and UV-B resistance were enhanced by 15-17% and 12-16%, respectively, based on the median lethal responses of the trxA conidia to the thermal stress of 75 min at 48 degrees C (LT50) and the UV-B irradiation of 312 nm weighted wavelength at the gradient doses of 0.1-1.2 J/cm(2) (LD50). However, the wild-type and transgenic strains equally responded to the hyperosmotic stress of 0.5, 1.0 or 1.5 M NaCl in growth medium. The results indicate that the transgenic approach is effective in enhancing the thermotolerance and UV-B resistance of B. bassiana and that the transgenic strains are potential for use in developing more field-persistent formulations. (C) 2011 Elsevier Inc. All rights reserved.