Bioactive Metabolites from Talaromyces purpureogenus , an Endophytic Fungus from Panax notoginseng
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BIOACTIVE METABOLITES FROM Talaromyces purpureogenus, AN ENDOPHYTIC FUNGUS FROM Panax notoginseng
Li-Xi Feng,1 Bing-Yang Zhang,1 Hua-Jie Zhu,1 Li Pan,2* and Fei Cao1*
Secondary metabolites from endophytic fungi are rich and have many biological activities, including promoting plant growth, antibacterial, anticancer, and anti-inflammatory properties [1]. Studies on endophytic fungi to discover natural products with significant activities show great economic value and application prospects [2, 3]. For example, a series of azaphilone derivatives [4], isocoumarin derivatives [4], diphenylketones [5], xanthones [5], benzofurans [6], sesquiterpene-conjugated amino acids [7], and diphenyl ether derivatives [8] has been obtained from the endophytic fungus Talaromyces sp. These compounds exhibit different physiological activities. In order to further discover compounds with novel structure and activities, the endophytic fungus Talaromyces purpureogenus XL-25 isolated from Panax notoginseng was selected as our research object for fermentation. All of the isolated compounds were identified by detailed spectroscopic analysis [9] and by comparison with the data of those previously reported in the literature. The structures of compounds 1–6 were established as talaroconvolutin A (1) [4], talaroconvolutin B (2) [4], 3-hydroxy-5-methylphenyl-2,4-dihydroxy-6-methylbenzoate (3) [10], 8-hydroxy-6-methoxy-3methylisocoumarin (4) [11], 6,8-dihydroxy-3-methylisocoumarin (5) [12], and purpurester A (6) [13], respectively. The antibacterial activities of all the isolated compounds (1–6) were evaluated against six pathogenic bacteria strains. Among them, compound 1 showed pronounced antibacterial activity against Bacillus subtilis with an MIC value of 1.56 μM, which was close to the positive control ciprofloxacin (MIC = 2.5 μM). Compound 2 had a certain inhibitory activity against Micrococcus lysodeikticus (MIC = 0.73 μM) and Vibrio parahaemolyticus (MIC = 0.18 μM). Fungus Material. The fungal strain Talaromyces purpureogenus (XL-25) was isolated from the fresh tissue of Panax notoginseng, which was collected from medicinal plants from Shijiazhuang, Hebei Province, China, in May, 2016 and identified by ITS sequence. The strain was deposited at the Key Laboratory of Medicinal Chemistry and Molecular Diagnostics of the Education Ministry of China, Baoding, P. R. China, with the GenBank accession number KY230505.1. Culture Conditions. The fungus of Talaromyces purpureogenus was dissected under aseptic conditions and placed on PDA agar plates (comprising 2% glucose, 2% agar, 20% potato in distilled water). The plates were wrapped in parafilm and incubated at 28°C for 3–4 days. Then the fungus of Talaromyces purpureogenus XL-25 was set in small scale in rice medium (100 mL water, 100 g rice, 2.0 g glucose, 20 g peptone) in 1 L Erlenmeyer flasks. Sixty flasks of the fungal strain were incubated at 28°C for 60 days. Extraction and Isolation. The fermented solid medium was extracted two or three times with EtOAc until the organic phase was almost
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