Preliminary Studies On Separation Of Antifungal Agricultural Antibiotics And Optimization Of Fermentation Conditions

A strain of Streptomyces lydicus AS 4.2501 had been obtained from the soil and reserved in our lab. It was able to produce some antibiotics, which could inhibit cotton Rhizoctonia solani, wheet scab, Alternaria solani and other 15 pathogens. Therefore, these antibiotics have enormous potentiality to be developed as industrial products thanks to their strong bioactivity. In this paper, firstly the medium composition was optimized in flask scale, and then applied it in 2L fermentor to study the fermention kinetics of Streptomyces lydicus AS 4.2501. Finally, the antibiotics were purified by adsorption, solvent extraction and silica gel column chromatography.Firstly, with Rhizoctonia solani as the indicator microorganism, we optimized the medium composition in flask scale through uniform design and orthogonal experiments. The result showed that the percentage of fungistasis rose from 65.9% to 78.6% with the optimized medium, which was 19.2% higher than the original one.Secondly, the fermention process in 2L fermentor scale was studied through monitoring reducing sugar, cell dry weight, pH and dissolved oxygen. The result showed the lag phase of the strain growed with the optimized medium was remarkably shortened compared with that with the original one. After 30 hours of fermentation, the cell dry weight reached the peak value of 13.3mg/mL, which was 44.6% higher than the control. The maximum percentage of fungistasis was 83.1%, which was slightly higher than that of the original medium. However, the culture time was reduced from 54h to 36h.Finally, the pretreated fermention broth was adsorbed by activated carbon and Diaion HP-20 macroporous adsorption resin respectively. The concentrated eluant was extracted by equal-volume n-butyl alcohol, and the organic layer was concentrated and chromatographed on a silica gel column with chloroform-methanol-29% ammonia water (5:3:1). Purified active fractions were obtained from the corresponding eluate. The MS analysis result showed three peaks with m/z of 432.2, 579.2 and 574.0 were detected in the samples separated by activated carbon, while two peaks with m/z of 654.3 and 625.4 were detected in the samples separated by Diaion HP-20 macroporous adsorption resin. Both groups had strong antifungal activity, thus it was concluded that there were multiple antifungal antibiotics in the broth.