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

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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.