SUMMARY: Genetic transformation was investigated among spp. whose normal habitat is the nasopharynx of humans. Seven species, as characterized in (1957), were represented. Deoxyribonucleate (DNA) preparations from streptomycin-resistant mutants of , and conferred resistance upon streptomycin-susceptible parent strains of the corresponding species (intraspecific transformation) and of each other species (interspecific transformation). Ratios of interspecific to intraspecific transformation were 0.01 or higher for all possible combinations of DNA and recipient cells of the six species. On the other hand, cells, which exhibited high frequencies of intraspecific transformation, were not transformed at detectable frequencies by DNA from any of the six species listed above. In turn, DNA from had little or no transforming activity for these other neisseriae.

Possible evidence of structural differences between these DNA's was sought by analysing the base contents of transforming preparations. The bases adenine, thymine, guanine and cytosine were present in about equal proportions in the DNA's of the six and . In DNA preparations from two strains of , however, adenine and thymine predominated. The ratio (adenine + thymine/guanine + cytosine) was higher than 1.4 compared to 1.0 for the others.


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