Optimization of solid-state fermentation conditions for Trichoderma asperellum strain TCS007 and antibacterial activity of crude extracts

The previous research indicates that Trichoderma asperellum TCS007 possesses the abilities of antifungal activity, plant growth promotion, and induction of plant stress resistance, while its metabolites exhibit stronger antifungal activity against Sclerotinia sclerotiorum. To improve the yield of crude solid-state fermentation extracts of TCS007, the medium composition and fermentation conditions were optimized using single-factor experiments in combination with response surface methodology (RSM), with S. sclerotiorum as the target pathogen. The results showed that the three major factors influencing the yield of crude solid-state fermentation extracts were fermentation time, soybean powder addition, and water addition. The optimized fermentation medium and conditions were as follows: 72 g of rice, soybean flour at 3.5% (m/m) of the rice, 47 mL of water, 1 mL of inoculum (1 × 10⁷ spores/mL), a 29 days of fermentation period, a 12 h light/12 h dark photoperiod, a 28 °C incubation temperature, and an initial pH of 7.0. Under these conditions, the yield of crude fermentation extracts reached 1.21 g, which was in good agreement with the predicted yield of 1.22 g using response surface methodology, representing a 1.34-fold increase compared with the initial fermentation conditions. Furthermore, shallow-pan cultivation further increased the yield to 1.45 g. At a concentration of 50 μg/mL, the optimized crude fermentation extracts inhibited the growth of S. sclerotiorum, Marssonina coronaria, Botrytis cinerea, and Rhizoctonia solani by 96.87%, 77.42%, 71.07%, and 62.50%, respectively. The antifungal activity test targeting S. sclerotiorum showed that the EC₅₀ value of the crude extracts obtained under the initial fermentation conditions was 17.91 μg/mL, whereas that decreased to 0.51 μg/mL after optimization, indicating a 35-fold enhancement in antifungal activity. In addition, the optimized extracts significantly inhibited sclerotial formation by 63.93% and suppressed sclerotial germination. These findings provide a theoretical basis for further development of fermentation processes for biocontrol microbial pesticide products by T. spinosum TCS007.