Characterization of the Bacterial Development and Antifungal Properties of Bacillus thuringiensis var. kurstaki HD-1 Obtained by Bioconversion of Agroindustrial Effluents

Large-scale production of Bacillus thuringiensis, one of the most widely used biopesticides, is often limited by the high cost of conventional culture media. In this study, fermented cassava paste water (EFM), ripe mango pulp juice (CM), and cashew apple juice (JPC) were evaluated as alternative substrates for the liquid fermentation of B. thuringiensis var. kurstaki HD-1. Physicochemical analyses revealed acidic pH values and classified the substrates into two clusters: CM with high C/N ratios, organic matter, total sugars, and proteins, and EFM and JPC with lower C/N ratios and nutrient levels. Fermentation results indicated that JPC supported the highest biomass production (8.29 × 1013 CFU mL−1), exceeding that in the standard Tryptone Soy Broth (TSB) medium. However, CM promoted the highest sporulation rate (1.46 × 1013 CFU mL−1) and the greatest bioactive lipopeptides—iturins (102.2 mg L−1) and surfactins (554.7 mg L−1)—surpassing TSB. The antifungal activity of crude fermented CM, EFM, and TSB was evaluated against Sclerotium rolfsii. All samples significantly inhibited mycelial growth of the pathogen with no significant differences among substrates or concentrations tested. This study highlights the potential of B. thuringiensis-fermented agrowaste as a cost-effective, environmentally friendly biocontrol tool for Sclerotium rolfsii.