[Medium optimization for antagonistic Streptomyces S24 and its inhibition on Aspergillus flavus].

Streptomyces S24 has broad spectrum against Aspergillus spp. in food and feed, such as Aspergillus flavus, Aspergillus niger and Asperegillus alutacells. The objective of this study was to improve the production of antifungal substances produced by S24 and to test their inhibitory effects on Aspergillus flavus. By using one-factor-at-a-time experiment and orthogonal design method, we optimized the fermentation medium. The composition of an optimized medium for the production of antifungal substances contained (g/L): starch soluble, 10; Glucose, 40; yeast extract, 8; soybean powder, 24; KH2PO4 4; and CaCO3 0.8. As a result, the productivity of antifungal substances could reach to 10 235.45 microg/mL, and this value was 2.81 times higher than that of initial medium before optimization. Additionally, inhibitory effects of the products on Aspergillus flavus were analyzed. Antagonistic tests indicated that the antifungal substances greatly inhibited mycelium growth and spores germination of Aspergillus flavus. We observed through microscope that the mycelia grew abnormally, such as contorting, bulging, vacuole increasing and the cytoplasmic contents inside effusing and the spores appeared unusual, such as gathering, deforming, cytoplasmic contents inside effusing and fracturing.

[Isolation, purification and characterization of antifungal substances from Streptomyces hygroscopicus BS-112].

OBJECTIVE: In order to provide the basis for application of Streptomyces hygroscopicus BS-112 and its antifungal active substances, we isolated and purified the active substances produced by strain BS-112, and then we examined their chemical structures and determined their inhibitory effects on Aspergillus flavus. METHODS: We extracted and purified the antifungal active substances from strain BS-112 using column chromatography with X-5 macroporous resin and 200 - 300 mesh silica gel respectively, and then purified them by preparative HPLC with Venusil XBP C18 column. The chemical structures of active components were identified by means of spectroscopic analysis, including mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR). Their minimum inhibitory concentration and minimum fungicidal concentration against Aspergillus flavus were determined by the standard broth microdilution method. RESULTS: We obtained four active components from the fermentation broth of strain BS-112 and their chemical structures were the same as Tetrins A and B, Tetramycins A and B. Assay using 96-well plate illustrated that the MIC of Tetrin A, Tetrin B, Tetramycin A and Tetramycin B against Aspergillus flavus were 3.13 microg/mL,12.56 microg/mL,1.56 microg/mL and 6.25 microg/mL respectively, and their MFC were 6.25 microg/mL, 25.0 microg/mL, 3.13 microg/mL and 12.56 microg/mL respectively. CONCLUSION: The antifungal active substances of strain BS-112 were composed of four compounds, Tetrins A and B, Tetramycins A and B. The four active compounds showed strong inhibitory against Aspergillus flavus.

[Extraction and characterization of antifungal substances produced by antagonistic Streptomyces S24].

Streptomyces S24 has broad spectrum resistance to the Aspergillus in food and feed, such as Aspergillus flavus, Aspergillus niger, Asperegillus alutacells and so on. We studied the adsorption and desorption properties of antifungal substance from Streptomyces S24 on macroporous resins, screened the best elution solution and also investigated some physical and chemical characters of antifungal substance by determining the antifugal activity using oxford plate assay system. According to the analysis results, AB-8 resin offered the best adsorption and desorption capacity for antifungal substance and its saturated absorption capacity was 7.0822 x 10(4) microg/g, the optimal elution solution was 85% acetone and the dynamic desorption rate could reach 93.82%. The antifungal substance was stable to heat and alkali, not sensitive to organic solvents, and sensitive to ultraviolet rays and acid. Based on its ultraviolet spectrometry, the antifungal substance was identified as heptaene macrolide antibiotic.