Engineering a thermostable recombinant Bacillus thuringiensis serovar tenebrionis expressing a date palm dehydrin gene for improved red palm weevil biocontrol.

Abstract

The efficacy of Bacillus thuringiensis based biopesticides under field conditions is frequently compromised due to the thermal degradation of δ-endotoxins at elevated temperatures. Dehydrins (DHNs) are highly hydrophilic and intrinsically disordered proteins characterized by flexible structures and the ability to interact with a wide range of cellular molecules, including proteins, enzymes, membranes, and ions. These properties enable DHNs to protect and stabilize cellular macromolecules and help maintain cellular functions under adverse environmental conditions. In this study, B. thuringiensis serovar tenebrionis was engineered to express the date palm DHN gene PdDHN1, and its performance was compared with wild-type and empty vector strains after defined thermal preconditioning at 28 °C and 45 °C for 7 days before application. After heat-stress preconditioning, the PdDHN1-expressing strain retained the highest sporulation capacity (16.5 × 10⁷ spores/ml), exceeding both the wild-type strain (11.8 × 10⁷ spores/ml) and the empty vector strain (9.2 × 10⁷ spores/ml). Bioassays against red palm weevil (RPW), Rhynchophorus ferrugineus showed that the recombinant strain had stronger insecticidal activity than the control strains under both thermal regimes, causing faster survival decline and greater mortality. PdDHN1-transformed formulations reduced RPW larval and adult survival to below 10% after 21 days, whereas the wild-type and empty-vector strains showed a lower reduction in RPW survival. Feeding efficiency assays showed physiological disruption in insects exposed to the PdDHN1-transformed B. thuringiensis strain; in larvae, feed conversion efficiency (FCE), efficiency of conversion of ingested food (ECI), and efficiency of conversion of digested food (ECD) decreased by 73.72%, 70.65%, and 66.86%, respectively, compared with wild-type and empty vector strains. In adults, ECI and ECD were reduced by 70.65% and 63.40%, respectively, under the same conditions. The expression of PdDHN1 enhances B. thuringiensis thermal stability and insecticidal efficacy under heat stress, providing an approach to improve biopesticide performance in high-temperature environments.