| Bioactive ingredients were screened from endophytic microorganisms of Circaeasteragristis, a Ranunculaceae plant in this investigation. We report here the isolation,purification, and identification of microorganism strains, as well as the evaluation ofantimicrobial activity and identification of active ingredients of the metabolites ofpreferred strains. The main results are as follows:Taking different separating culture medium and isolating methods,48strains ofendophytic fungus and35strains of actinomycetes were separated from the leaf, stem, rootof Circaeaster agristis, respectively.The metabolite of the above mentioned microorganisms was subjected to evaluate theirantibacterial activity by diffusion method and their antifungal activity by the method ofmycelial growth. Sixteen antibacterial and nine antifungal strains were obtained finally, andthe most potential strains, actinomyces G10, H18and fungus PG6,were preferred forfurther investigation.Strain G10was recognized a streptothricin producer by a reliable fast identificationmethod. In view of that streptothricin has been registered as an agro-fungicide in China,whereas no analysis method was reported up to now. A method based on LC-MS/MStechnique was established in this investigation, and it could be used to the quality control ofraw materials and formulations. The results of precision and accuracy tests indicated thatthe established method was validated.Actinomycetes H18was identified as Streptomyces alboflavus313by conventionalclassification principle. Two novel cyclic hexapeptides, designated NW-G08and NW-G09,were isolated from the fermentation broth, and their structures were elucidated on thebasis of extensive spectroscopic analysis, MS experiments, and chemical analysis. Theyexhibited highly antibacterial activity against gram-positive bacteria, whereas they did notinhibit gram-negatives. It is worth noted that the novel cyclic hexapeptides exhibited muchhigher activity against methicillin-resistant Staphylococcus aureus (MRSA) than ampicillin,which implies they might be potential candidates for the development of novel drugs againstresistant pathogenic bacteria.The endophyte PG6was identified as Byssochlamys nivea. Guided by the results of the bioassay, one active compound have been separated from the fermentation broth of the strainPG6and named as Q6. The minimum inhibitory concentration (MICs) of Q6againstStaphylococcus aureus, Escherichia coli, Bacillus subtilis, Bacillus cereus and Pseudomonasaeruginosa were25,12.5,25,6.25,50ug/ml, and it also exhibited inhibitory effect on sporegermination of botrytis cinerea. Because of the yield can be up to1g/L and the separationmethod is simple, the compound has the potential for industrialization production. |
