Electrotransformation of streptococcus with lacotococci plasmid and investigation of the factor of dental caries by oral microorganisms

1.从乳酸乳球菌JK301pGB301中提取pGB301，采用碱式十二烷基硫酸钠和超速离心法提取。琼脂糖凝胶电泳法证实为单一条带。米氏链球菌10707、血链球菌ATCC 35105和高登链球菌35105的电转化及转化效率研究通过转化，微生物在红霉素平板上生长。其效率为1.5×10~(-4)~5.5×10~(-4)，电穿孔效率提高了5倍。在发酵液的光密度为0.1的条件下收获微生物效果最好。米氏链霉菌10707低pH敏感突变株的构建亲本菌株在pH为4.2的发酵液中生长。另一方面，突变株不能在pH为4.6的发酵液中生长。转化效率为1.4x103cfu/μG.4。最有效的电转化条件当峰值电压为2.5kv，电容为25F，脉冲控制为200Ω，收获光密度为0.5.5时，电转化效果最好。口腔微生物对β-半乳糖的致龋性及相关酶的活性变形链球菌不利用β-半乳糖和乳糖基果糖。

1. Extraction pGB301 from Lactococcus lactis JK301pGB301 was extracted by means of alkali-SDS and ultracentrifusion. A single band was confirmed on agarosen gel electrophoresis.2. Electrotransformation of Streptococcus milleli 10707, S.sanguis ATCC 35105 and S.gordonii Challis and its efficiencyThe strains of the microorganisms were cultured in Todd-Hewitt broth sulpplemented with 5% horse serum. The microorganisms grew on plate with Erythromycin by the transformation. Its efficiency was ranged form 1.5×10^4 to 5.5×10^4. The effciency increased five times by electroporation. It was most effective whhen the microorganisms were harvested at 0.1 of optical density of the broth.3. Construction of low-pH sensitve mutansts of S.milleli 10707.Low-pH sensitve mutansts of S.milleli 10707 were constructed with ethyl methasulfonete. The parent strain grew in the broth of pH 4.2. On the other hand the mutant did not grow in the broth of pH 4.6. Its transformation efficiency was 1.4 ×10^3 CFU/μg.4. The most effective condition for electrotransformationThe most effective condition for electrotransformation was obtained when peak voltage was 2.5 kV, capacitance was 25 F, pulse controll was 200Ω and harvest OD was 0.5.5. Cariogenic factos of β-galacto-sugars by oral microorganisms and the activity of the enzymes involvedMutans streptococci did not utilize β-galactosyllactose and lactosylfructoside.