Diversity, antibacterial and phytotoxic activities of culturable gut fungi from the insect <i>Anax parthenope</i>

AIMS: Insect gut fungi, as specialized symbiotic microorganisms, represent a valuable source for the discovery of novel bioactive metabolites. This study aims to explore the diversity and bioactivity of culturable gut fungal communities in Anax parthenope. METHODS AND RESULTS: A total of 53 fungal strains from the gut of A. parthenope were distributed across three classes in 22 genera. Antibacterial tests showed that 10 strains exhibited antibacterial activity against at least one pathogenic bacterium. Phytotoxic tests indicated that 16 strains showed significant phytotoxic activity against Echinochloa crusgalli with inhibition rates exceeding 80%, and 11 strains showed potent phytotoxic activity against Abutilon theophrasti with inhibition rate exceeding 70%. Furthermore, four metabolites were isolated from the Alternaria sp. QZB-4. Compound 2 exhibited moderate antibacterial activity against Pseudomonas syringae pv. actinidiae (Psa) and Xanthomonas oryzae pv. oryzae (Xoo), with inhibition zone diameter (IZD) of 17.0 and 11.7 mm respectively, which were comparable to those of the positive gentamicin sulfate. Compound 3 also showed moderate antibacterial activity against Xoo and Xanthomonas oryzae pv. oryzicola (Xoc) with the IZD of 12.2 and 12.3 mm, respectively, which were less effective than those of positive control. In addition, at a concentration of 100 μg·mL-1, compounds 1 and 3 exhibited strong phytotoxic activity against E. crusgalli and A. theophrasti, with inhibition rates of 90% and 93%, respectively, which were slightly lower than those of the positive 2,4-Dichlorophenoxyacetic acid with the inhibition rate of 100%.