| Endophytic fungi, which are the important part of host’s microecosystem, colonize in thecells or the intercellular space of the health plant tissues such as roots, stems and leaves. Theydo not cause the obvious diseases to the host in general. Recent studies have shown thatendophytic fungi isolated from the medicinal plants could produce the same or similarbioactive substance as their host, which provide valuable resources for the development ofnew drugs, and have extensive application prospects. In this paper,75strains endophyticfungi were isolated from the Chinese traditional medicinal plant Du Zhong (Eucommiaulmoides) and the antimicrobial activity of their metabolites was studied.75strains endophytic fungi were isolated from healthy roots, stems and leaves ofEucommia ulmoides which collected from Jiangsu yancheng. Among them,22strains wereisolated from leaves,19strains from stems, and34strains from roots. The separation rate was16.34%,21.33%and36.27%, respectively. The distribution of endophytic fungi in Eucommiaulmoides tissues was varied. The most endophytic fungi were isolated from root tissues. Itmight be due to the growing environment of root tissues.The antimicrobial activity of the metabolites secreted by75strains Eucommia ulmoidesendophytic fungi was studied. The percentages of all strains which had strong antimicrobialactivity against E. coli, B. subtilis, S. aureus, Sh. dysenteriae and S. typhimurium was30.67%,21.34%,17.33%,12%and16%, respectively. The metabolites of endophytic fungus Y18possessed strong antimicrobial activity against5pathogenic bacterias. The Y18strain wasidentified as Fusarium equiseti based on the morphological observation and ITS sequenceanalysis. The biological characteristics of Y18strain were as follow: the optimumtemperature was30oC, the optimum pH was7, the glucose and beef extract were the mosteasily used carbon and nitrogen source. However, lighting showed little impact on the growthof Y18strain.Detected by flow cytometer and conductivity meter, the cell membranes of E. coli andS. aureus were damaged extensively after the treatment of the metabolites of Y18. Therelative electric conductivity of E. coli bacteria liquid was16.22%and the percentage ofPI-stained E. coli reached25.31%after4hours; the relative electric conductivity of S. aureusbacteria liquid was14.5%and the percentage of PI-stained S. aureus reached19.64%after4hours. These results showed that, the metabolites of Y18could destroy the structure of cellmembrane and affect its permselectivity and biological activity.The effects of the metabolites from strain Y18on the cytological bioactivity ofpathogenic bacteria were further studied by Fourier Transform Infrared Spectroscopy (FT-IR).Significant changes were happened on the cell membrane, protein and DNA with the treatment of the metabolites of Y18. In the whole cell protein structure of E. coli, the contentof β-fold structure increased from34.60%to41.47%, while the proportion of random coilstructure dropped obviously from21.80%to18.67%and the proportion of α-helix and β-turnalso reduced. Accompanying these changes, the structure of nucleic acid were altered; InS. aureus, the β-fold structure and random coil increased from30.37%,23.59%to34.97%and27.48%, respectively. While the proportion of α-helix, β-turn reduced from27.46%,18.58%to21.33%and16.22%, respectively. The results of circular dichroism furtherindicated that the DNA structure might became loose because the stacking interactions ofbases were weakened with the treatment of the metabolites of Y18.Analyzing the basic composition of the metabolites, the results show that，somesubstances such as peptide, alkaloids, saponins, flavonoids, and organic acid, existed in thewater phase, but substances such as terpenoid substances and phenols were not detected. Themain substances were alkaloids and flavonoids in the ethyl acetate phase, and further researchwould focus to confirm what kind of material it is. |
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