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.