Screening And Analysis Of Streptomyces Roseoflavus Men-myco-93-63 Blocked Mutants

Streptomyces roseoflavus Men-myco-93-63 was a strain isolated from potato scabdecline soil by Professor Liu Daqun, which could inhibit many pathogen fungus andbacteria in lab. And the fermentation liquid had a strong antibiosis activity against cottonverticillium wilt and cucurbits powdery mildew in greenhouse and field. The effectiveelements and function mechanism were under study.The blocked mutants were useful materials to deduce the way of antibiotics production.In this paper, an agar gel model for mutation pre-screening by selective indicatormicroorganism Verticilliumdahliae was built up. The spores of Streptomyces roseoflavusMen-myco-93-63 were mutated by ultraviolet radiation (UV), LiCl, microwave irradiationand diethyl sulfate (DES). Six blocked mutant strains named as MV11, MV18, MV21,MV22, MV35 and MV40 thathad no antifungal ability were screening from its parentstrain Streptomyces roseoflavus Men-myco-93-63 by microwave irradiation and twoisolated after being treated by DES named as DE01 and DE02. The 8 mutants were stableafter ten subcultures.No significant effects on morphological differentiation were observed. The apparentdifferences between mutants and Men-myco-93-63 were as follows. The color of substratemycelia turned light Seven mutants changed gray-green and also resulted in moreproduction of spores, while the other strain turned to black and spores ouput less. Theantibiotic spectrum of mutants was studied. They had no antibiosis against 8 targetpathogens. 16S rDNA sequence analysis was made. There existed obvious distinctions andthe mutational hot spots were similar in different mutants. The crude antibiotics extractedfrom mutants mycelia were analyzed by HPLC. The peaks in Men-myco-93-63 vanishedand new peaks appeared in the mutants.Every two of the eight blocked strains were tested by cosynthesis. DE02 and MV40could cosynthesize antibiotics. The fact that MV40 was secretor while DE02 wasconverner illuminated the blocked site in MV40 was after DE02 in the secondarymetabolism. It may be caused by the variation of enzyme genes involved in the antibioticsynthesis. Otherwise, the rest mutants could not be as secretor or converner.