Diversity, antimicrobial and herbicidal activities of actinomycetes and fungi from Hermetia illucens.

Actinomycetes and fungi have been found to be important sources of bioactive natural products. Evaluation the diversity of culturable insect-asscociated microorganisms, and screening strains with bioactive activity holds a promising for the development of lead compounds. Here, the diversity, antimicrobial and herbicidal activities of culturable actinomycetes and fungi from Hermetia illucens was investigated for the first time. A total of 34 strains of actinomycetes and 27 strains of fungi were isolated from the gut and body surface of H. illucens. Among them, Streptomyces (97.1%) and Geotrichum (14.8%) were the most abundant genera in actinomycetes and fungi, respectively. The herbicidal bioassay showed that the fermentation broth of 3 actinomycetes and 13 fungi presented good inhibition activity (> 50%) against Echinochloa crusgalli and Abutilon theophrasti. The antibacterial bioassay showed that the crude extracts from 10 strains of actinomycetes (29.4%) displayed antibacterial activity against at least one pathogenic bacterium with the inhibition zone diameter (IZD) of 7.0-22.0 mm at the concentration of 30 µg/6 mm filter paper disc. Especially, the strain of S. tritolerans MFT2 exhibited strong antibacterial activity against S. aureus with the IZD of 22.0 mm, which were comparable to that of the positive gentamicin sulfate (IZD = 24.7 mm). Total of four known compounds were isolated from MFT2 by column chromatography, and were further identified as gilvocarcin M (1), gilvocarcin V (2), γ-valerolactone (3), and chrysomycin C (4) based on NMR and MS. Among them, compounds 1-2 exhibited moderate antibacterial activities against P. syringae pv. actinidiae with the IZD of 10.3 and 13.2 mm respectively at the concentration of 30 µg per disc, which were weaker than that of gentamycin sulfate (IZD = 25.7 mm). Furthermore, both compounds 1 and 2 exhibited moderate phytotoxicity against E. crusgalli with inhibition rate of 56.7% and 44.1% at a concentration of 100 µg/mL, respectively. In conclusion, the rich sources of actinomyces and fungi associated with H. illucens offers promising avenues for discovering novel antimicrobial agents and bioherbicides.