Transformation by plasmid and chromosomal DNAs in Haemophilus parainfluenzae.

An efficient procedure for transformation of $\text{H. parainfluenzae}$ by plasmid DNA is described. The procedure involved a new technique for preparation of competent cells that increased the transforming efficiency of a chromosomal str^r marker about 20 fold and that of the plasmid amp^r about 100 fold. The addition of either Mg²⁺ or Ca²⁺ promoted the stimulation of plasmid amp^r by another factor of 50, however, the chromosomal str^r marker was not further affected. The total stimulation of plasmid transformation was a factor of 5000 and the final ratio of amp^r to str^r activity was 1 to 100. These results suggested that plasmid and chromosomal DNAs have different specific requirements for transformation.