Abstract:

The purpose of this study is to isolate and identify culturable fungi from forest litter, to find the strains with antimicrobial activity and to study their main antimicrobial metabolites, so as to provide alternative strains for further development and utilization of fungal resources in forest litter. This study used the particle separation method to isolate the culturable fungi in forest litter, internal transcribed spacer (ITS) sequence analyses to identify isolated fungi, well diffusion method to detect antimicrobial activity, column chromatography method to separate antimicrobial monomeric compounds, and spectrum analyses to determine their chemical structure of the monomeric compounds. A total of 63 fungal strains were isolated, belonging to 36 genera and 48 taxa, among which, 14 strains had less than 98.5% of ITS similarity. Ethyl acetate crude extracts of 11 strains had antimicrobial activity, and Berkleasmium sp. SGSF622 had strong antimicrobial activity. The fungus was fermented in PDA medium, and 3 g of ethyl acetate extract was obtained. By bio-guided separation of antimicrobial activity, antimicrobial compound 622A with the highest content was obtained. By NMR and HR-MS analyses, this compound was further identified as Sch53825 and the molecular formula was C₂₀H₁₃ClO₅. Its minimal inhibition concentration of antibacterial activity against Ralstonia solanacearum was 125-250 μg/mL. It is the first time to separate Sch53825 from fungi of genus Berkleasmium. The study can lay a foundation for further development and utilization of fungal resources from forest litter.

Key words: litter fungi, Berkleasmium, antimicrobial activity, secondary metabolism, compound separation