Nucleic acid homology as a measure of genetic compatibility among streptococci and a strain of Diplococcus pneumoniae

A correlation has been observed between the degree of DNA–DNA (deoxyribonucleic acid) hybridization and the frequency of interspecific genetic transformation between Streptococcus species of serological groups D and H and Diplococcus pneumoniae. The thermal denaturation (T m ) values and guanine plus cytosine (G + C) mole percent for all cultures were similar. Two mutants of the group D streptococcus, resistant to the potent antileukemic drug amethopterin, were found to be more alike than any other two organisms studied. The intraspecific genetic transfer of the thymine-requirement marker in either direction was not successfully demonstrated. The lack of transformation of amethopterin resistance to the wild type organism was partially due to the lack of homology between the mutants and the wild type.