Studies On The Secondary Metabolites From Three Soil Actinomycetes Strains

Soil actinomycetes can produce a wide variety of bioactive natural products and are an important source of antibiotics.Among those antibiotic,the ansamycin antibiotics are a group of unique macrocyclic lactams with 3-amino-5-hydroxybenzoic acid(AHBA)as the starting unit.Because of its biological activity,it has become our research goal to discover novel ansamycins with potency potential from soil actinomycetes.Based on the necessity of the AHBA synthase in the biosynthetic pathway of ansamycins,and the high conservation of AHBA synthase genes in different actinomycetes,Dr.Song Rentai obtained 80 AHBA synthase genes positive strains in soils across the country via AHBA synthase gene targeted-PCR screening.In this study,three strains of AHBA-positive genes,Streptomyces sp.S051,Streptomyces sp.S006 and Streptomyces sp.S035 were used as research materials to study their secondary metabolites.A total of 29 compounds were isolated by column chromatography on Sephadex LH-20,RP-18,Si gel and HPLC.The structures of compounds were identified by UV,MS,NMR,and X-ray single crystal diffraction techniques,of which 12 were new compounds,including 1 naphthoquinone,4 dinorsesterterpenoids and 7 pentaketide ansamycins.Eight compouds were isolated from the YMG medium of Streptomyces sp.S051,including one new naphthoquinones compound A13(4).No ansamycins were isolated.We infered that ansamycin gene cluster was either low or no expression in this strain.Seven compouds were isolated from the waksman synthetic medium of Streptomyces sp.S006,including four new dinorsesterterpenoids(B12,B13,B4 and B6,12-15).The antimicrobial activity of compounds 12-15 were evaluated,but no evident activity was observed.No ansamycins were isolated.We deduced that ansamycin gene cluster was either low expression or no expression.The mutant S035-SL was constructed by co-expressing the positive regulator factors LAL and SARP in the ansamycin gene cluster.Through the isolation of the secondary metabolites of oatmeal medium of the mutants S035-SL,a total of compounds were obtained,including 7 new pentaketide ansamycins(SL31,SL27,SL14,SL6,SL8,SL12 and SL13,16-22).HeLa,SW480,PC3 and HCT116 cell lines were selected for cytotoxicity assays of compounds 16-22.Compounds SL6,SL27 and SL14 all showed cytotoxicity,and SL8 and SL12 showed selective inhibition activities on different cell lines.