Heat stress priming enhanced conidial germination, insect virulence and metabolic adaptation in Beauveria bassiana

Beauveria bassiana strains are commercially available as mycoinsecticides and are widely used for insect control. However, its effectiveness is often hindered by vulnerability to environmental stressors such as UV radiation, drought, and heat. Exposure to moderate heat, which is considered a triggering stimulus, partially inhibits the germination of conidia. This study investigated the impact of heat stress and priming on conidial germination, radial growth, sporulation, virulence to insects, and metabolic profiling in B. bassiana BCC 2660. The conidial germination significantly suppressed and declined from 82 to 34 % at 45 °C after 180 min. Here, we introduced a priming state to enhance the fungus's tolerance to the triggering stimulus. Comparative analysis revealed that conidia subjected to heat-induced priming at 35 °C for 40 min exhibited a significant increase in germination from 32 to 65 %, compared to non-primed conidia. The primed conidia also demonstrated a reduction in the LT₅₀ by 10 h in comparison to their non-primed counterparts. While priming improved germination, it did not significantly affect radial growth or sporulation rates under heat stress. We further explored the memory time of priming, finding that the fungus retained the priming state for up to 4 h. To elucidate the molecular mechanisms underlying the heat stress response, we identified candidate metabolites using LC-MS. Metabolomic analysis identified 34 metabolites, with significant alterations in metabolic pathways related to spermidine biosynthesis, coenzyme A synthesis, fungal wall development and various cellular process among primed conidia. These results underscored the complex metabolic adjustments in B. bassiana conidia, highlighting the potential of priming strategies to enhance fungal tolerance to environmental stresses and improve biocontrol efficacy in agricultural applications.