Structures And Bioactivities Of Secondary Metabolites From Four Deep-Sea Cold-Seep Fungi

The deep sea is an important part of the marine system,which contains unique and extreme living environments such as deep-sea seamounts,oceanic ridges,hydrothermal fluids and cold seep.Compared with other source microorganisms,deep-sea microorganisms have unique genetic background and metabolic pathways due to their living environments.In recent years,a large number of microorganisms have been isolated from deep-sea sediments,which are the main source of them.Furthermore,many novel secondary metabolites have been obtained from the microorganisms.Cold seeps,typical deep-sea chemosynthesis-driven ecosystems,are characterised by their richness in methane and hydrogen sulfide,which also result in high abundance and unique metabolic pathways of cold seep-derived microorganisms.Overview of the research on cold seep at home and abroad,the research on cold seeps is still in its infancy.Besides,secondary metabolites of cold-seep derived microorganisms have only been reported in recent years.Therefore,the study on the secondary metabolites of cold-seep derived fungi can enrich the structures of marine natural products.It also helps us to understand the adaptation mechanism of microorganisms in extreme environments and provides a theoretical basis for us to explore deep-sea resources.Forty four fungal strains were isolated from 4 sedment samples,which were collected from deep-sea cold seep of southeast Hainan and southwest Taiwan.Subsequently,4 fungal strains were detected as potential strains based on biomass,TLC analysis results and bioactivity test results.Thereafter the fungal species were identified and the possible metabolites were predicted,while the chemical structure and biological activity of their secondary metabolites were studied.The subjects included Penicillium oxalicum 13-37,Cladosporium halotolerans 9-39,Aspergillus sydowii 10-31 and P.chrysogenum 13-35.The compounds were obtained by silica gel,Sephadex LH-20,RP-18,and semi-preparative HPLC,etc.The structures of the compounds were identified by NMR,MS,IR and ECD,as well as by comparision with literatures.49 compounds were isolated from Penicillium oxalicum 13-37,including 3 new phenylhydrazones（PO1-PO3）,2 new quinazolines（PO4 and PO5）and a xanthone derivative（PO6）.Thirty seven compounds were characterized from Aspergillus sydowii 10-31,including 2 novel compounds（AS1 and AS2）and 35 known compounds.Eighteen compounds were isolated from Cladosporium halotolerans 9-39,with structural types covering steroids,benzene derivatives,lactones and peptides,while 17 compounds were isolated from the culture extract of P.chrysogenum 13-35,with structural types covering terpenes,alkaloids,steroids,indoles,etc.Some of the compounds were evaluated for bioactivities.As a result,some compounds showed great antimicrobial activities,bright antimiciroalgal activities and low toxicity to brine shrimp.For instance,PO1 could remarkably inhibit the the hytoplankton species,and the IC₅₀ values could be 0.68μg/m L.What′s more,it showed moderate inhibition against Vibrio harveyi and V.parahaemolyticus,and the inhibition zone diameters exceeded 10 mm at 20μg/disk.Addictionally,it possessed low toxicities to Artemia salina.In summary,the chemical structures and bioactivities of the secondary metabolites of the deep-sea cold-seep derived fungi were investigated.Besides,121secondary metabolites were isolated,including phenylhydrazones,quinazolines,steroids,terpenes,polyketides,peptaibols,indoles,benzene derivatives and alkaloids,etc.Among them,8 compounds were found to be new strutures.The diversity of compound species enriches the types of secondary metabolites of microorganisms of deep-sea cold seep fungal origin,and also provides theoretical references for further understanding of microbial adaptation mechanisms and metabolic pathways in extreme environments.The screening of secondary metabolites with good antimicroalgal activity provides a theoretical basis for the protection and development of the marine environment.Furthermore,the compounds with great antimicrobial activity are beneficial for the preparation of bacterial inhibitors and the structural modification and synthesis of new drugs.