Enhancing Bacillus thuringiensis Performance: Fertilizer-Driven Improvements in Biofilm Formation, UV Protection, and Pest Control Efficacy

This study investigated the effects of fertilizers on the biofilm formation, ultraviolet (UV) resistance, and insecticidal activity of <i>Bacillus thuringiensis</i> (Bt). <i>Bacillus thuringiensis</i>, a widely used microbial pesticide, has a minimal environmental impact and is highly effective against specific pests but is susceptible to environmental factors in field applications. Bacterial biofilms provide protection for Bt, enhancing its survival and functionality in the environment. However, the mechanisms by which fertilizers regulate the characteristics of microbial pesticides and enhance biofilm formation are not well understood. This study evaluated the effects of six fertilizers on the bacterial biofilm formation, the UV resistance, and the insecticidal activities of Bt wettable powders. The results demonstrated that fertilizers significantly enhanced the performance of three Bt preparations (Lv'an, Kang'xin, and Lu'kang). A compound fertilizer with 8.346 g/L of KCl, 2.751 g/L of ZnSO₄·7H₂O, and 25.681 μL/mL of humic acid was identified by response surface optimization, achieving the maximum BBF formation with OD₅₉₅ value of 2.738. Furthermore, KH₂PO₄, HA, and ZnSO₄·7H₂O notably improved the survivability of Bt preparations under prolonged UV exposure, with the compound fertilizer providing the greatest protection. What's more, fertilizers reduced the LC₅₀ values of all Bt preparations, with the compound fertilizer decreasing the LC₅₀ of the Lv'an Bt wettable powder to 0.139 g/L, a 3.12-fold increase in efficacy. This study demonstrated that fertilizers significantly enhance the UV resistance and insecticidal activity of Bt wettable powders by promoting bacterial biofilm formation. Herein, this study provides new strategies and theoretical support for Bt applications in modern sustainable agriculture.