Enhancing The Chemical Diversity And Bioactivities Of Secondary Metabolites From Marine-derived Fungi By Epigenetic Modification

Natural products are important source of developing new drugs,especially those from marine-derived fungi which possess novel structures and significant biological activities have attracted more and more attentions.The whole genome sequencing studies of fungi have indicated that most genes of fungi were silent and not expressed in the conventional experimental training conditions.It has been a hot pot nowadays to search for new and bioactive compounds using the strategy of epigenetic modification.In the dissertation,secondary metabolites and their bioactivities for four marined-derived fungi were researched using the strategy of epigenetic modification.One hundred and six compounds were isolated and elucidated from four marine-derived fungi,Penicillium adametzioides AS-53 from an unidentified marine sponge,Aspergillus ochraceus MA-15 from the rhizosphere soil of marine mangrove plant Bruguiera gymnorrhiza,Penicillium citrinum MA-197 from the leaves of mangrove plant Lumnitzera racemosa,and Talaromyces stipitatus MA-205 from the mangrove plant Rhizophora stylosa Griff.Seventeen of the compounds were new structures and two of the others were new natural compounds.Antimicrobial,cytotoxic,as well as brine shrimp?Artemia salina?lethality were measured for the compounds.The preliminary research of the fermentation of P.adametzioides AS-53 using the strategy of epigenetic modification was reported in this dissertation.The results showed that different fermentation factors of this fungus could produce diverse secondary metabolites.Two fermentation conditions were performed and different compounds from each fermentation extracts were isolated.Thirty-one compounds were isolated and elucidated from the cultivation on a liquid potato-dextrose broth?PDB?culture medium of the fungus,five of which were new structures,including four bisthiodiketopiperazines?PAP1^PAP4?and one spiroquinazoline?PAP6?.Nine distinct compounds were isolated from a rice solid culture medium of this fungus,including two new acorane sesquiterpenes?PAR1^PAR2?.All these compounds were examined for antimicrobial and cytotoxic activity as well as brine shrimp?Artemia salina?lethality.New compound PAP1 showed brine shrimp lethality,with LD₅₀ value of 4.76 ?M,and the positive control colchicin was 8.09 ?M.Furthermore,PAP1 showed potential activity against Staphyloccocus aureus,Aeromonas hydrophilia,Vibrio harveyi,V.parahaemolyticus,and Gaeumannomyces graminis with MIC values of 8.0,8.0,32.0,8.0,and 16.0 ?g/mL,respectively.Newcompound PAR2 showed selective activity against the NCI-H446 cell line with IC₅₀ value of 5.0 ?M,while the positive control doxorubicin was 4.0±0.4 ?M.Twenty-eight compounds were isolated and elucidated from the extracts of A.ochraceus MA-15,six of which were new compounds,including five polyketides?AO1^AO3,AO8,AO15?and one phenolic derivative?AO19?.Twenty-three compounds were isolated and elucidated from the extracts of P.citrinum MA-197.Eighteen compounds were isolated and elucidated from the extracts of T.stipitatus MA-205,including four new diphenyl ester compounds?TS1^TS3,TS6?and two new natural products?TS7,TS17?.These compounds were tested for their antimicrobial,cytotoxic,and brine shrimp?Artemia salina?lethality.Compounds AO1 and AO13 exhibited inhibitory activities against A.hydrophilia,V.anguillarum,V.harveyi,with MIC values of8.0,16.0,8.0 and 1.0,32.0,0.5 ?g/mL,respectively,and the positive control chloramphenicol was 4.0,1.0,8.0 ?g/mL.Compound PC5 showed inhibition activity against S.aureus with MIC value of 4.0 ?g/mL,which was two times as much as positive control?chloramphenicol?,while compound PC18 showed strong antibacterial activity against Micrococcus luteus,with MIC value of 0.25 ?g/mL,and the positive control chloramphenicol was 2.0 ?g/mL.Compounds PC13 and PC15 showed considerable inhibitory activities against Colletotrichum gloeosprioides and G.graminis with MIC values of 4.0 and 2.0 ?g/mL,respectively.The research for fermentation explored the potential of the fungus to produce secondary metabolites,and became successful application for epigenetic modification in fungal secondary metabolites.