Study On The Bioactive Secondary Metabolites Of Symbiotic Microorganism From Stony Coral Diploria Strigosa Of The South China Sea

Marine microorganism possesses special metabolic approach to produce thecompounds with new structures and significant activities. Recently, more and moreresearches on the secondary metabolites of symbiotic microorganism isolated from coralwere reported, such as gorgonians and soft corals. However, reports on the secondarymetabolites of stony corals have not been reported up to date. There were kinds of stonycorals living in Coral Reef National Nature Reserve of Xuwen, Zhanjiang, Guangdong. Astony coral named Diploria strigosa was collected here and studied systematically in thispaper including isolation and active screening of symbiotic microorganism from the stonycoral, isolation of the bioactive metabolites from the active microorganism, structureanalysis of the compounds, determination of pharmacological activities (DPPH scavenging,erythrocyte hemolysis inhibitory, acetylcholinesterase inhibitory activites), extraction andDPPH scavenging activity determination of Extracellular polysaccharides (EPSs) from astrain of actinomyces.Adopting gradient dilution method,17strains of symbiotic microorganisms wereisolated from the stony coral with8srains of bacterias,4strains of actinomyces and5strains of fungis. The Actinomyces ZJG1and the fungi ZJP1were selected by DPPHscavenging method and fermented to150L and20L, respectively. With various ofseparation technology such as silica gel column chromatography, Sephadex LH-20andpreparative thin layer chromatography, and with structure determination methods of IR, UV,1D NMR,2D NMR and MS,12compounds were isolated and identified with5compoundsfrom fermentation liquid of ZJG1and7from ZJP1. Pharmacological activities of the compounds were tested by DPPH scavenging method,erythrocyte hemolysis and acetylcholinesterase inhibition methods. The results showed thatZJG13exhibited potent antioxidant activity, with the value of DPPH scavenging IC502.06μg/mL, erythrocyte hemolysis inhibition IC506.37μg/mL. Both ZJG12and ZJG13exhibitedacetylcholinesterase inhibitory activity with inhibition ratios of74.37%and96.58%at theconcentration of0.166mg/mL. ZJG16exhibited moderate inhibitory activity to erythrocytehemolysis with the value of IC5011.53μg/mL.Three kinds of EPSs were obtained from the mycelium and fermentation broth of thesymbiotic actinomycete ZJG1respectively with hot wate extraction,95%ethanolsubsidition, Sevag assay clearing protein, H2O2discoloration and different concentration ofethanol subsidition. The EPSs contents of the mycelium were71.26%、91.03%、81.66%,and the EPSs contents of the fermentation liquor were86.18%、57.67%、76.29%by Phonol-sulphuric method. The EPSs showed weak antioxidant activity by DPPH free radicalscavening assay.In conclusion, according to the study of secondary metabolites of two symbioticmicroorganism isolated from stony coral Diploria strigosa,12compounds were isolatedand identified. By the pharmacological activities testing, several compounds showed theantioxidant and acetylcholinesterase inhibitory activity. The results showed that themetabolites from the symbiotic microorganism of the stony coral Diploria strigosa canprovide lead compounds for marine anti-Alzheimer drugs. What’s more, the study of thesymbiotic microorganism isolated from the stony coral was important for finding thecontinuable substitute of stony coral and protecting coral reef ecosystem.