Targeted Discovery Of Novel Natural Products From Lysobacter And Novel PoTeMs In Saccharopolyspora Hirsuta DSM 44795

The discovery of antibiotics with a novel structure and mode of action is a pressing need due to the constant emergence of clinical drug-resistant pathogens and new pathogens.Bioinformatic analysis indicated that the largely unexplored Lysobacter strains contain abundant cryptic secondary metabolic pathways.However,only several natural products have been isolated from Lysobacter.Polycyclic tetramate macrolactams(PoTeMs)have a good application prospect in agricultural pathogens control and medicine development because of their distinctive chemical structures,impressive physiological activities and unique biosynthetic mechanisms.Therefore,exploration of the novel secondary metabolites from Lysobacter and targeted discovery of new PoTeMs will lead to the identification of new bioactive natural products.In this thesis,we carried out the following three projects:1.Targeted discovery and biosynthesis of lysohexaenetides in Lysobacter sp.DSM 3655.We analyzed the genome sequence of strain 3655 and found a novel PKS/NRPS gene cluster,BGC9,which was then reconstructed and introduced into Streptomyces sp.S001.As a result,two novel PK/NRP compounds,lysohexaenetides A(1)and B(2),were obtained from the metabolites of the recombinant strain S001-BGC9.In addition,the biosynthetic pathway of lysohexaenetides was proposed,but the formation of the initial carboxyl group of the polyketide chain remains to be elucidated.It is worth noting that the single module PKS is responsible for the synthesis of polyunsaturated polyketide chain of lysohexaenetides,that is rare for bacterial type I PKS.2.Targeted discovery of novel cyclic lipopeptides octabacins in Lysobacter enzymogenes SR10.Previously,we identified a novel NRPS gene cluster in strain SR10,and constructed a mutant strain,SR10ΔHSAF,to felicitate the isolation of other metabolites.In this study,four new cyclic lipopeptides,octabacins A-D(3-6),were obtained from the metabolites of SR10ΔHSAF.Octabacins A-D(3-6)exhibited activity against Bacillus subtilis and Staphylococcus aureus.The biosynthetic pathway of octabacins was also proposed.3.Targeted discovery of sahamide A in Saccharopolyspora hirsuta DSM 44795.Previously,we identified a novel PoTeM biosynthetic gene cluster sah in the database,and constructed the recombinant strain SR111-PoTeMsah,which contained the refactored sah gene cluster.In this study,a novel PoTeM,sahamide A(7),was obtained from the metabolites of the above strain.Sahamide A(7)is the first 5-membered monocyclic PoTeM with oxidative modification.Sahamide A showed weak activity against Pythium aphanidermatum.In addition,according to the chemical structure of sahamide A(7),we speculated that the cytochrome P450 in the sah gene cluster could catalyze the C-3 hydroxylation of ornithine,while the previously reported PoTeMs-related P450 could only catalyze the oxidative modification of the polyketide moiety.In conclusion,we obtained 7 new natural products through genome mining.The antibacterial activity of the isolated compounds was evaluated,and the biosynthetic pathways of them were proposed.Our results indicated that the "pathway reconstruction-heterologous expression" strategy can not only effectively mine new natural products of Lysobacter,but also be suitable for targeted discovery of new PoTeMs,which set a foundation for genome mining of Lysobacter and new PoTeMs.