Study on Secondary Metabolites and Antibacterial Activity of Three Forest Litter Fungi in Daxing’anling Mountains
Fungal species are abundant and can produce a variety of secondary metabolites, including antibacterial compounds that can be applied in the fields of medicine and pesticides. The decomposition of forest litter depends on the diversity of fungi, and forest litter is also considered a good habitat for fungi. The fungal resources in the forest litter of Daxing’anling are abundant. Zhang et al. found that the extracts of six fungi in the forest litter of Daxing’anling have antibacterial activity, and four monomeric compounds were obtained from two fungi. Qiu isolated two monomeric compounds with antibacterial activity from forest litter fungi in the Greater Khingan Range. This study used three strains of forest litter fungi with antibacterial activity in the Greater Khingan Mountains as materials to isolate and identify the main antibacterial compounds they produced. A total of eight compounds were obtained (see Figure 1), including two new structure natural products and five compounds with antibacterial activity. This study lays the foundation for further utilization of antibacterial compounds produced by forest litter fungi.

In this study, eight compounds were isolated from three forest litter fungi SGSF622, SGSF289, and SGSF062 in the Greater Khingan Range, including two new compounds, 1-methoxy-Ch53825 (1) and 3,4-dihydroxy-10-methyl-2-methylenetetradecyl-9-enoic acid (2). Their planar structures were analyzed, but their stereoisomers need further investigation, and their optical rotation and other spectral data also need to be supplemented. The stereostructure of the compounds in this article was obtained by comparing the nuclear magnetic data in the literature, and their accurate absolute configuration still needs further research. The three fungal genera belonging to this study have all been reported to have natural product structures and biological activities. Berkleismum fungi have been reported to have antifungal, antibacterial, and anti-tumor activities. In 2009, Cai et al. isolated a mixture of diepoxin eta and diepoxin zeta, as well as diepoxin kappa, from the fermentation broth of the endophytic bacterium Berkleismum sp. Dzf12. They have a similar structure to compound 1 in this study and belong to the class of spironaphthalene compounds. The article also reported their effects on Escherichia coli, Agrobacterium tumefaciens, and X. vesicatoria. The cucumber leaf spot pathogen (P. lachrymans) and Bacillus subtilis have good inhibitory activity. Oidiodendron fungi have been isolated from 10 methoxydihydrofuscin, fuscinarin, and fuscin. These compounds were found to effectively bind to macrophage inflammatory protein (MIP) -1R and human CCR5, which is an important anti-HIV-1 target that can interfere with HIV entry into cells. These compounds were not found in this study. Qiu isolated the natural product of Parapyenchaeta fungus SGSF449 and separated the metabolite 4,6,8-trihydroxy-7-methoxy-3-methyldihydroisocoumarin from its fermentation product. This compound was first isolated from Scytalidium and named lignicol, which is consistent with the chemical structure of compound 6 in this article. This study reports for the first time the spectral data of compound 1 and compound 2, as well as the antibacterial activity of compounds 2 and 3. Except for compound 6, all other compounds were isolated for the first time from the fungal genera belonging to the three fungi. This study enriches the research on natural products of forest litter fungi in the Greater Khingan Range, laying the foundation for further development and utilization of forest fungal resources in the Greater Khingan Range.