| Actinomycetes have a distinguished advantage in the field of antibiotics: about 75% of antibiotics are produced by actinomycetes of which 75% are produced by streptomyces sp. Most antibiotics from soil streptomyces are still used widely. To solve the problem of microbes'resistance, it is urgent to discover new antibiotics from microbes. Besides soil streptomyces, other sources of microbes should be taken into account. Because of their particular living environment, endophytes have produced special metabolites with unusual chemical structure and have been the important source of microbe secondary metabolite.In this study, Trewia nudiflora, an arboreal found in the tropical rain forest of Yunnan Province, was chosen as experimental material. Seven actinomycetes were isolated from the seeds of T. nudiflora. A2 was identified as streptomyces sp. according to morphological character and 16s rDNA analyses. The strain was cultured on plates up to 2 liters, the extracts were analyzed by LC-MS and the chloride-containing peaks were observed with the characteristic of [M]+: [M+1]+:[M+2]+=3: 1: 1. It had the same retention time with maytansin. For further research, the strain was cultured on plates up to 18 liters, five compounds were isolated, and their structures were elucidated as (+)nonactic acid,homononactic acid and macrotetrolide, 1-acetate- 4-hydroxy- benzeneethanol, 5-Methyl-6-acetylresorcinol ,but no chloride-containing peaks were detected.Streptomyces sp. XM201 were cultured on YEME media. The extract was isolated and 5 compounds were purified, and their structures were identified as nigericin, 30-acetyl nigericin, 1-O-methyl-30-acetyl nigericin, 1,29-O-dimethyl-30-acetyl nigericin, 29-O-methyl abierixin. Lebstatin and 17-O-demethyl-lebstatin were isolated from pJTU813/△asm25 Streptomyces sp.XM201. 4'-O-demethyl nanchangmycin was isolated from Streptomyces nanchangensis n. sp. Yan et Ouyang⊿M.The bioactivities of nigericin and it's derivatives were also studied. In the serial dilution assay, nigericin and 30-acetyl nigericin showed strong activities against Staphylococcus aureus ATCC25923 and Bacillus cereus 1126, and their MIC were 0.125μg /ml and 0.125μg /ml, respectively. No inhibitory activities were observed against Candida albicans AS2.538 and Escherichia.coli CMCC44103 at the concentration of 25μg /ml. nigericin and 30-acetyl nigericin showed distinguished effects on the regeneration clones of B.cereus 1126 and E.coli CMCC44103 at concentration of 1μg /ml, whereas 1-O-methyl-30-acetyl nigericin, 1,29-O-dimethyl-30-acetyl nigericin and 29-O-methyl abierixin did not. The cytotoxic activity of nigericin was tested with HEPG2 cell line with the IC50 value as 0.36μg /ml. The results of activities suggested that C30-hydroxyl has no obvious correlation with activity, but C1-carboxylate is necessary for nigericin.From the endophyte Streptomyces sp. A2, four products were isolated from the second of two fermentations. However, maytansinoids were not detected in the second fermentation; it is not certain whether streptomyces sp. A2 produces maytansinoids. Further study may answer this question.Nigericin and its derivatives have been isolated from YEME media fermentation of Streptomyces sp.XM201, and the bioassays for their structure-activities relationships will give more information to understand the complex structure and physico-chemical requirements for antibiotic activities.
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