An Antifugal Antibiotic Produced By A Strain Of Nocardioform Actinomycetes LA5

The study on morphology and evaluation of Actinomyces LA5- Strain of Actinomyces was carried out; it showed strong antagonism against pathogenic fungus, Phytophthara capscum for example. Further study tells that it is the antibiotic LA5 which isolated from Actinomyces's fermentation broth has the antagonism ability. The separation and purification method, structure analysis, action mechanism and control effect in vivo of antibiotic LAS were conducted. The results showed as follows:1. Isolate LAS was morphologically, biochemically and physiologically tested and was identified to be Nocardioform Actinomycetes.2. The compound of antibiotic LAS, pure crystal was isolated from the fermentation broth by Ion exchange chromatography combined with crystallization. The pure crystal of antibiotic LAS is light-yellow prism,which activly against pathogenic fungus. By means of UV spectroscopic analysis it is identified as antibiotic LAS which belongs to nucleoside family. The water-soluble and alkali scent antibiotic LAS maintains its activity at the condition of neutral, alkaline, light, 54 for 15 days respectively. Antibiotic LAS loses activity when deposited for half a year; its inhibition activity fell down to half when deposited for a year at normal condition. The estimate titer for fermentation is tested by method of colorimetry.3. Studies on mechanisms of antibiotic LAS action showed that growth of hyphae was inhibited at low concentration of antibiotic, and can be totally inhibited at high concentration. After treated with antibiotic LAS, the characteristic of Phytophthora capscum hyphae changed significantly, hyphae puffed up and became short, the cell wall was getting unintegral, with nearly disappeared cell chorion inside which only a little remainder and lipid stockpile particle left. UV spectroscopic analysis indicated that action site of LAS is not in cell membrane. Antibiotic LAS may interfere in the DNA synthesization of the pathogen. It also interfered in the sporangium formation, spore release and bourgeoning,4. Control effect of LAS performed in vivo indicated LAS was a high effect antibiotic. 10 times concentrated fermentation gave significantly protective activity against the development of Phytophthora disease on pepper plants. The disease control effect was better than that of commercial fungicides that is 600 times diluted metalaxyl, and slightly less than that of 400 times dilution metalaxyl.This is the fkst study on antibiotic isolation from Norcadioform actinomycetes which demonstrate antagonism activity against P. capsici in vitro and in vivo .It is worth to conduct the further study on the antifungal activities in animal and in human beings as well.