Genomic Analysis Led To The Discovery Of Indolecarbazole Alkaloids Produced By Marine Streptomyces IMB3-202

The emergence and spread of drug-resistant bacteria has become a great challenge for the clinical treatment of infectious diseases.It is urgent to develop new drugs against drug-resistant bacteria.Antibiotics with novel structures from the traditional terrrestrial actinomycetes has declined.The discovery of a series of novel compounds from marine microorganism has attracted widespread insterest for marine actinomycetes.In addition,the progress of genome sequencing technology makes it possible to predict the structure of microbial products at the genetic level.Therefore,based on genome sequence technology,the analysis and discovery of new natural products from marine actinomycetes has become a research hotspot in recent years.This dissertation focused on the isolation,purification,structural identification and activity evaluation of antibiotic compounds from the marine-derived actinomycete Streptomyces sp.IMB3-202.Genomic analysis by AntiSMASH revealed that one gene cluster in Streptomyces sp.IMB3-202 genome displayed high similarity to the biosynthetic gene of indolecarbazole alkaloids,suggesting that the strain has the potential of produce indolecarbazoles.Guided by bioinformatics analysis,four compounds(1～4)were isolated and identified from the fermentation broth of Streptomyces sp.IMB3-202 by optimizing the fermentation conditions and various chromatographic methods.The structures of compounds were identified by spectroscopic methods including UV,IR,MS,ID and 2D NMR.The structures were identified as staurosporine(1),3’-O-demethylstaurosporine(2),holyrine A(3)and K252c(4).The in vitro antibacterial bioassay showed that staurosporine(1)showed antibacterial activity against Pseudomonas aeruginosa 11 with an MIC value of 64μg mL-1 and weak antibacterial activity against Staphylococcus aureus and Candida albicans with an MIC value of 128μg·mL-1.Compounds 1-3 displayed potent cytotoxicity against human cancer Hela(hepatocellular carcinoma),HCT116(human colorectal carcinoma),and MCF-7(breast adenocarcinoma)cell lines with IC50 values ranging from 0.75 to 1192.8 nM.To stimulate the expression of silent genes in Streptomyces sp.IMB3-202,co-cultivation of strain IMB3-202 with 50 marine actinomycetes strains,2 fungi,and 6 pathogen strains.Co-cultivation of Streptomyces sp.IMB3-202 with four marine-derived actinomycete strains produced new metabolites which were not present in the pure cultures.