| Plant endophyte, a natural microorganism, inhabiting in the tissues and apparatus of plant and having no obvious harm to plant itself, can be separated from the inner part of disinfected plant. Plant endophyte is a big group with various kinds. As a kind of endophyte, antimicrobial endophyte is a potential source of novel chemistry and biology to be applied in not only new drug research and development of the medical, but also the biological control of plant diseases in agriculture. Now we are just at the beginning of the research on endophytes, and many of their characters have not been understood deeply. As a novel materials inhabited by endophytes, the traditional medicinal plants are becoming the objectives of the endophytic researchers. In this scientific dissertation, the medicinal plants Paris polyphylla var. chinensis Franch were chosen as the materials for separation of endophytes. The antimicrobial endophytes were screened and the strain with remarkable antimicrobial effect was identified by the traditional characterization and the molecular characterization. It was studied preliminarily about the crude separated conditions of antibiotic substance and its related properties.79 strains of endophytes have been separated from the underground tuber tissues of Paris polyphylla var. chinensis Franch, a traditional medicinal plant which is collected at Pengzhou county, Sichuan province in southwest China, included 7 fungi, 3 actinomycetes and 69 bacteria. By preliminary antimicrobial screening against pathogenic bacteria, 21 endophytes which had antimicrobial activity against one or two kinds of pathogenic bacteria were obtained. Through further screening against plant pathogenic fungi, there were 13 endophytic bacteria with antimicrobial activity against one or several kinds of plant pathogenic fungi, in which 5 endophytic bacteria had better antimicrobial activity against all plant pathogenic fungi in test. The strain Iun35 with best antimicrobial activity was selected to the next series of studies.Based on the characteristics of morphology, physiology and biochemistry as well as the 16S rDNA analysis, the strain Iun35 was classified into Bacillus subtilis. The strain was tested for antagonism toward 5 plant pathogenic fungi by measuring its growth rate. The results showed that its inhibitory rates against Pyricularia oryzae Cav, Pestalotia funereal, Rhizoctonia solani Kuha , Curvularia lunata (Walk) Boed. and Gibberelle zeae ( Schw. ) Petch were 80.5%,71.9%,70.5%,83.3%,57.1% respectively.The antibiotic substance produced by the strain Iun35 can be fractionally precipitated by ammonium sulfate with series of concentration, then the solution of precipitation was precipitated again by acetone under low temperature. The crude extracts containing antibiotic substance was obtained from the supernatant treated with acetone by vacuum rotary evaporation. Through the stability test of pH and temperature and the proteinase sensitivity test, it was obvious that the antibiotic substance is a quite stable material. After dialysed by dialysis-bag (22mm, 14 000D), the antibiotic substance was still presented in the dialysis-bag which showed that the molecular weight of the antibiotic substance was no lower than 10kD. The crude extracts have a widely antibiotic spectrum, and possessed inhibitory effect against 13 plant pathogenic fungi, included Rhizoctonia cerealis, Sclerotinia sclerotiorum and Physalospora piricala etc. The results demonstrate that the strain Iun35 has a wonderfully potential application in biological pesticide and antibiotic production.
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