RÉSUMÉ
Three hundred and twenty endophytic actinobacterial strains were isolated from psammophytes collected from Taklamakan Desert and identified.Among them,three strains already had been identified as new species of two genera and sixteen isolates showed relatively low 16S rRNA similarities＜98.6％to validly described species.Seventy-five of the isolates were selected as representative strains to screen antibacterial activity and mechanism.Forty-seven strains showed antagonistic activity against at least one of the indicator bacteria.Two Streptomyces strains produced bioactive compounds inducing DNA damage,and two Streptomyces strains produced bioactive compounds with inhibitory activity on protein biosynthesis.Notably,the strain Streptomyces sp.8P21H-1 that demonstrated both strong antibacterial activity and inhibitory activity on protein biosynthesis was prioritized for exploring new antibiotics.Under the strategy of integrating genetics-based discovery program and MS/MS-based molecular networking,two new streptogramin-type antibiotics,i.e.,acetyl-griseoviridin and desulphurizing gri-seoviridin,along with known griseoviridin,were isolated from the culture broth of strain 8P21H-1.Their chemical structures were determined by HR-MS,and 1D and 2D NMR.Desulphurizing griseoviridin and griseoviridin exhibited antibacterial activities by inhibiting translation.