Integration efficiency in DNA-induced transformation of Pneumococcus. I. A method of transformation in solid medium and its use for isolation of transformation-deficient and recombination-modified mutants.

A method of transformation on solid medium especially adapted for pneumococcus has been developed. Under specific conditions, all colonies that are allowed to grow in the presence of transforming DNA for six hours give rise to transformed bacteria. Combined with replica plating this technique has been used to isolate mutants modified with regard to recombination. Most of the mutants found are transformation-defective and show a large diversity in their response to ultraviolet light. Some of these mutants have lost their ability to take up transforming DNA. One shows a reduced yield of transformants for a given quantity of DNA taken up. Mutants that manifest altered behavior with regard to marker efficiencies have also been isolated. One of these exhibits a decrease in the transformation efficiency of only the high efficiency markers and two mutants show a decrease in the transformation efficiency of the low efficiency markers.

Integration efficiency in DNA-induced transformation of Pneumococcus. II. Genetic studies of mutant integrating all the markers with a high efficiency.

Transformation of the pneumococcus mutant 401 by DNA's bearing the standard reference marker and several other markers belonging to two unlinked loci has shown that differences in the integration efficiencies of these markers were considerably reduced in this strain compared to the wild-type strain Cl(3). The sensitivities of mutant 401 to ultraviolet light and to X-ray irradiation are the same as those of Cl(3). However, in 401 all the markers tested are more resistant to inactivation as shown by transformation of 401 and Cl(3) by ultraviolet-irradiated DNA. The increase in resistance is greater for low efficiency (LE) markers than for high efficiency (HE) markers.-The decreased discrimination between LE and HE markers in strain 401 is not due to a mechanism related to modification of markers in the transforming DNA by the recipient cells, nor are the proteins inducing competence of the cells responsible for the differences in the integration efficiencies of various markers.-Genetic studies of the fate of recombinants as well as the measure of the amount of DNA taken up have shown that all the markers are integrated in strain 401 by the same recombination process, that specific to high efficiency markers.