Study On Secondary Metabolites From Some Gene Inactivation Mutant Of Streptonigrin Biosynthesis In Streptomyces Flocculus Cgmcc 4.1223

Streptonigrin(STN),produced by Streptomyces flocculus,is an aminoquinone alkaloid with broad-spectrum activities such as antibacterial,antifungal,antiviral and antitumor properties.Recently,its biosynthetic gene cluster has been successfully cloned and identified.To obtain streptonigrin analogues with high efficiency and low toxicity by manipulating the biosynthetic pathway of STN,we generated some gene inactivation mutants.We identified 12 compounds,including 4 new compounds from 4 of the mutants.Firstly,we optimized fermentation conditions,and Amberlite XAD-16 resins were used in fermentation to improve the production of the metabolites in the mutants.The compounds were then purified by using normal phase silica gelcolumn chromatography,reverse phase silica gel column chromatography column,or gel chromatography packed with sephadex LH-20.The chemical structures of compounds were elucidated by spectroscopic technologies including nuclear magnetic resonance(NMR)and high-resolution mass spectroscopy(HR-MS).Among the 12 compounds,K4-1 and R-1 were confirmed to be xantholipin and its analogue;K4-2,K4-4,K4-5 were confirmed to be?-carboline alkaloids;R-3,D-2,D-3,D-4,D-5,Q3 were confirmed to be STN analogues.R-1,K4-4,D-4,and D-5 are new compounds.The new compound of xantholipin analogue was named as xantholipin B.The biological assays showed that it displayed excellent antimicrobial activity against both Gram-positive bacteria and fungi.Importantly,both xantholipin and xantholipin B inhibited methicillin resistant Staphylococcus aureus Mu 50 strain with MIC value of 0.025 ?g/mL.xantholipin B also showed 6-11 fold activity to five selected human-related tumor cell lines than xantholipin.In this study,we found 3 ?-carboline alkaloids,which enrich the diversity of Carboline family.6 STN analogues set stage for discovery of more efficient and lower toxic analogues of STN,encouraging us to find more new and bioactive secondary metabolites.