Optimization of <i>Metarhizium koreanum</i> MN031-Mt 46: Nutritional Supplementation to Improve Conidia and Cuticle-Degrading Enzyme Production by Solid-State Fermentation

This study aimed to evaluate five different mixed agricultural wastes as potential substrates for solid-state fermentation (SSF) to produce conidia of <i>Metarhizium koreanum</i> MN031-Mt 46. Single-factor experiments and a Box-Behnken design (BBD) were employed to optimize the fermentation conditions for enhanced conidia yield. Results indicated that a mixed substrate comprising broken rice and rice bran significantly enhanced the optimal production of aerial conidia of MN031-Mt 46. Optimal fermentation conditions established through response surface methodology (RSM) revealed that with the addition of shrimp shell waste to the mixed substrate, conidia production increased to 8.45 × 10⁸ conidia per gram of dry substrate at 26.19°C temperature, 39.76% moisture, and 1.45% of shrimp shell waste after 301.87 h of incubation. Enhanced conidia performance indices were observed, including higher conidia weight, increased water content, and reduced residue post-harvest. The optimized fermentation conditions resulted in enhanced cuticle-degrading enzymatic activities, with maximum activities of 58.78 ± 2.29 U g^-1 ds for protease, 126.57 ± 6.47 U g^-1 ds for lipase, and 58.32 ± 0.78 U g^-1 ds for chitinase. These findings highlight the potential and versatility of mixed SSF using cost-effective agricultural waste for biopesticide and hydrolytic enzyme production, while promoting sustainable waste management and environmental pollution control, aligning with circular economy principles.