Jacob A E, Horton W A, Drucker D B
Department of Biochemistry and Molecular Biology, University of Manchester, Great Britain.
Microbios. 1989;60(244-245):167-75.
Only one of six Streptococcus milleri strains, known to produce dental caries in gnotobiotic rats, was found to be spontaneously transformable. At optimal competence (after 60 min incubation in transformation medium) DNA uptake by this strain, CR 287, was rapid; maximum DNA was taken up by cells within 15 min of its addition to give a transformation frequency of 1 x 10(-2) transformants per colony-forming unit (cfu). With post-optimally competent cells, the rate of DNA uptake was markedly decreased, although a transformation frequency similar to that of optimally competent cells was obtained. For example, after 240 min incubation in transformation medium the cells required approximately 90 min to reach maximum DNA uptake and gave a transformation frequency of 6 x 10(-3) transformants per cfu. Cultures retained the ability to give their maximum transformation frequency for at least 4 h, but only if a DNA-cell contact time of 2 h was used. Strain CR 287 and S. milleri strain NCTC 10707, a transformable non-cariogenic strain, produced competence factor (CF). The CF of CR 287, but not that of NCTC 10707, induced high competence in the non-spontaneously transformable cariogenic S. milleri strain NCTC 11169. Like S. sanguis, S. milleri must therefore produce CFs of different constitutional types. The three transformable strains could be transformed by plasmid shuttle cloning vector pVA838 DNA.
已知在悉生大鼠中可致龋齿的6株米勒链球菌中，只有1株被发现可自发转化。在最佳感受态时（在转化培养基中孵育60分钟后），该菌株CR 287摄取DNA的速度很快；在添加DNA后的15分钟内，细胞摄取的DNA量达到最大，转化频率为每集落形成单位（cfu）1×10⁻²个转化子。对于处于最佳感受态之后的细胞，DNA摄取速率明显降低，尽管获得的转化频率与处于最佳感受态的细胞相似。例如，在转化培养基中孵育240分钟后，细胞需要大约90分钟才能达到最大DNA摄取量，每cfu的转化频率为6×10⁻³个转化子。培养物至少在4小时内保持产生其最大转化频率的能力，但前提是使用2小时的DNA-细胞接触时间。菌株CR 287和米勒链球菌菌株NCTC 10707（一种可转化的非致龋菌株）产生感受态因子（CF）。CR 287的CF，而不是NCTC 10707的CF，能在非自发转化的致龋米勒链球菌菌株NCTC 11169中诱导出高感受态。因此，与血链球菌一样，米勒链球菌必定产生不同组成类型的CF。这三株可转化菌株可用质粒穿梭克隆载体pVA838 DNA进行转化。
