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用亚硝基胍处理对链霉素有强抗力的变链菌株6715 H S R而得到其变异菌株C_4。C_4的发酵糖模式,血清反应均与其上代6715H S R相同,但其合成不溶水葡聚糖的葡糖基转移酶(G T F)活动力较6715 H S R显著减低;粘附能力和菌斑形成能力也减弱,从而无致龋性。6715在M S培养基上呈枕状、粗而坚硬的菌落形态,C_4却呈高凸、光滑而软的菌落形态。因为C_4表现了遗传表型(Phenotype生物遗传素质中的外表可见部份)的基因多显性的变化(Pleitropic Change在遗传学
Streptomycin-resistant Streptomyces strain 6715 H S R was treated with nitrosoguanidine to obtain a mutant strain C_4. However, the activity of glucosyltransferase (GTF) of glucosyltransferase (Glucosyltransferase) was significantly lower than that of 6715 HSR, and the adhesive ability and plaque forming ability of C_4 were also decreased , So no cariogenic. 6715 had a pillow-shaped, coarse and hard colony morphology on MS medium, while C 4 showed a highly convex, smooth and soft colony morphology. Because C_4 represents a genetically dominant change in the phenotype (the visible part of the phenotype in the biological properties of the Phenotype) (Pleitropic Change in Genetics