Antimicrobial metabolites of the intestinal fungus Trichoderma sp. QTYC44 from Pantala flavescens larvae

BACKGROUND: Insect gut fungi are increasingly recognized as specialized microbial reservoirs of bioactive compounds, yet the insect-associated microbes of Pantala flavescens larvae remain understudied. RESULTS: In this study, the intestinal fungus Trichoderma sp. QTYC44, previously isolated from P. flavescens larvae, was further characterized and its antimicrobial metabolites were investigated. QTYC44 exhibited significant inhibitory effects on Fusarium oxysporum f. sp. cucumerinum with inhibition rates exceeding 80% and effectively suppressed cucumber wilt disease in a pot experiment, achieving 72.58% control efficacy. Chemical analysis of QTYC44 cultures led to the identification of 11 metabolites, including trichopyrone (1), bisvertinolone (2), vertinolide (3), (22E)-5a,8a-epidioxyergosta-6,22-dien-3b-ol (4), dihydrobisvertinolone (5), trichodimerol (6), bisorbibutenolide (7), ergosterol (8), uracil (9), adenosine (10), and palmitic acid (11). Antibacterial tests showed that compound 2 exhibited strong activity against Micrococcus tetragenus, Xanthomonas oryzae pv. oryzicola, and X. oryzae pv. oryzae, with inhibition zone diameters of 26.8, 17.7, and 22.0 mm, respectively, which were comparable or better than those of positive gentamicin sulfate. Further, compound 2 significantly reduced symptoms of bacterial leaf blight, achieving a control efficacy of 74.9% at 500 ng/ml, demonstrating strong in vivo antibacterial activity comparable to positive kasugamycin. SEM analysis revealed that treatment with compound 2 induced perforations in cell envelopes of X. oryzae pv. oryzae. In addition, compound 2 significantly enhanced lettuce growth, increasing aerial fresh weight by 70.8%. CONCLUSION: The results indicate that QTYC44 exhibits significant antimicrobial activity and holds great promise as a natural source of bioactive compounds for agricultural applications.