Source: http://ir.qdio.ac.cn/handle/337002/154470
Timestamp: 2019-04-20 01:14:49+00:00

Document:
Marine derived filamentous fungi (especially genera Aspergillus and Penicillium) are luxuriant sources of natural products with diverse scaffolds and bioactivities. Among them, fungi associated with marine algae and mangrove are a promising source for secondary metabolites research. However, the discovery of new compounds is getting more difficult, while the re-isolating of known compounds is becoming more frequently. On the other hand, many microbial biosynthetic genes related to secondary metabolites are silent or in lower transcription under a standard/common laboratory fermentation conditions. Recently, multiple approaches, such as co-cultivation, epigenetic manipulation, and genome mining, have been developed to activate its cryptic metabolic pathways and a number of new compounds were therefore identified.
During our ongoing study of bioactive secondary metabolites from marine algae and mangrove derived filamentous fungi, P. herquei MA-370, A. alabamensis EN-547, A. sydowii EN-534, P. citrinum EN-535 and A. nidulans MA-143 were selected as our target fungal strains, and we carried out a series of strategies such as modified fermentation medium (MA-370 and EN-547), cocultivation (EN-534 and EN-535) and revulsant addition (MA-143) to activate their cryptic biosynthetic pathways. As a result, a total number of 109 metabolites with diverse scaffolds were isolated and identified from the extracts of the above fungal strains’ fermentation, and 29 of them (including a new skeleton phenalenone derivative) were new compounds. All of the new compounds and some of the known were evaluated for their bioactivities and some of them showed potent value for drug development.
Thirty-nine secondary metabolites were isolated from P. herquei MA-370, seven of them were racemic phenalenones (HI 1-HI 7 and HI 10-HI 11, including 18 new stereostructures); HI 1 was a new skeleton compound, and HI 8 and HI 9 were two new α-pyrone analogues. The racemic phenalenones were analysized and some of them were successfully separated by chiral HPLC columns for the first time, and we have discussed the probable mechanism for their racemation. The absolute configurations of some of the racemic phenalenones were determined by ECD calculation. Twenty-one secondary metabolites were isolated from A. alabamensis EN-547. Among them, AL 1 and AL 2 are rare diketomorpholine derivatives whereas AL 3 is a highly conjugated ergostane-type steroid. Thirty-three secondary metabolites, including a new citrinin dimer (SC 1) and a new citrinin monomer (SC 2), were isolated from the coculture of A. sydowii EN-534 and P. citrinum EN-535. Sixteen compounds, including a new anthraquinone derivative (ND 1), a new xanthone analog (ND 2), and a new amino acid derivative (ND 3), were isolated from culture broth and mycelia extracts of A. nidulans MA-143 under 0.1 % ethanol stress.
All of the identified new compounds were tested for their antimicrobial activities against two human pathogens, five aquatic bacteria, and nine agricultural fungal pathogens. HI 2 showed potent inhibition against M. luteu, P. aeruginosa, V. alginolyticus, and V. parahemolyticus, which were comparable to the positive control chloramphenicol. HI 3 and HI 4 showed some inhibition against C. cornigerum, C. gloeosporioides, and V. mali, with MICs ranging from 16 to 64 μg/mL. AL 1 and AL 2 showed some inhibition against C. cornigerum, C. gloeosporioides, E. coli, F. graminearum, F. oxysporum, M. luteus, and V. mali with MICs ranging from 16 to 64 μg/mL. SC 1 and SC 2 showed some inhibition against E. ictaluri, F. graminearum, F. oxysporum, P. aeruginosa, V. alginolyticus and V. mali, with MICs ranging from 16 to 64 μg/mL. ND 1 and ND 4 showed some inhibition against E. coli, E. ictaluri, M. luteus, V. alginolyticus, and V. parahemolyticus, with MICs ranging from 1 to 32 μg/mL. ND 2 showed some inhibition against F. graminearum, F. oxysporum, and V. mali, with MICs ranging from 8 to 64 μg/mL. SC 1-SC 5 were further assayed for anti-influenza neuraminidase (NA) (homologous protein of H5N1) activity in vitro. SC 3 showed the best inhibition activity with IC50 12.9 nM.
In conclusion, our study provided positive evidence of strategies such as coculture and medium modification may activate the cryptic biosynthetic pathways of marine fungi, and broadened the structures of marine natural products.
GB/T 7714 杨遂群. 五株海藻及红树林来源真菌次级代谢产物的分子多样性挖掘与生物活性研究[D]. 中国科学院海洋研究所. 中国科学院大学,2018.

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