Study On The Isolation, Identification, Bioactivity And Secondary Metabolites Of Mangrove Actinomycetes

Nature products are important source of Medicine.Actinomycetes have a distinguished advantage in the field of antibiotics:about 75%of antibiotics are produced by actinomycetes,from the secondary metabolites of endophytic actinomycetes,a lot of compounds with new structures and great bioactive diversities could be found.Mangrove plants as important new resources for potential pharmaceutical because of their ecosystems that straddled the land and the sea,from freshwater to seawater,often with distinct microorganism species,have gradually attracted more and more attention of natural product chemists.From the leaves and roots of two mangrove plants(Kandelia candel and Aegiceras corniculatum)which collected from Fugong,Jimei,Haicang in Fujian Province,55 mangrove actinomycetes(endophytic or epiphytic)were isolated.In the investigation of antimicrobial activities,26 strains(about 47.3%of the total isolates)which showed antimicrobial activities against one or more sensitive microbes(Bacillus subtilis,Bacillus pumilus,Escherichia coli, Staphlococcus aureus,Candida albicans,Aspergillus niger)were screened out by using the agar diffusion assay.Using the method of MTT(Methyl Thiazolyltetrazolium),the isolates were screening for antitumor strains in vitro. The results showed that 5 strains(9.1%of the total isolates)could inhibit the growth of Hela and HepG2 tumor cell lines.The identification of the isolates by 16S rDNA assay indicated that only one strain belonged to Nocardiopsis while all the others belonged to streptomyces. The diversity of AHBA synthase gene was investigated using a pair of primers, AHBA R1-AHBA F.The KS domain of each isolate was amplified.6 strains could be amplified and amplification products displayed 700bp DNA bands, indicated DNA of these strains might have AHBA synthase gene.The strain Nocardiopsis sp.(No.3)and another bioactive strain streptomyces sp.(No.18)were selected to study their secondary metabolites. 13 compounds were isolated from strain No.3,including 3 new compounds(3C, 3Y-10)which were pyranones and 10 known compounds(3A,3Y-5,3Y-7, 3Y-14,3L-A,3L-M,3L-G,3Y-18,3Y-19,3Y-20).Within the 10 known compounds,3A,3Y-5,3Y-7,3Y-14 were derivatives of tryptophan,3L-A was glycerol 2-aminobenzoate,3L-M was hydroxybenzamide,3L-G was glycerol acetate,3Y-18 was acetyltyramine,3Y-19 and 3Y-20 were Cyclic dipeptides. From strain No.18,4 known compounds(18-C,18-F,18-E,18-G)were isolated,which were Methyl p-hydroxyphenylacetate,Dimethylα-ketoglutarate,2,6-dideoxypyranoside,2,6-dideoxypyranose,respectively.In the later investigation of the antimicrobial and antitumor bioactivities,the new compound 3C showed no antimicrobial bioactivity at 50μg/disk but weak antitumor bioactivity on Hela cell,the inhibition ratios were 2.73%and 7.39% when the concentrations of 3C were 10ug/mL and 20ug/mL.Our study indicated that mangrove plants included numbers of potent actinomycetes with antitumor and antimicrobial bioactivity,and that they were reliable resources for novel metabolites with antitumor and antimicrobial bioactivity at the same time.