Heterospecific transformation in the genus Haemophilus

The relationship between nine Haemophilus species and Haemophilus influenzae was studied by DNA-DNA hybridization, by transformation of H. influenzae to streptomycin resistance with heterospecific DNA, by competition of heterospecific DNA for transformation by homospecific DNA and by the lethal effect of heterospecific DNA on competent H. influenzae. H. parainfluenzae, H. parasuis, and H. aegyptius DNA transformed at more than 10% efficiency when compared to homologous transformation, but only H. aegyptius demonstrated, by hybridization, a relative binding ratio of more than 80%. H. aphrophilus and H. paraphrophilus DNA demonstrated a relative binding ratio of less than 30% and transformed H. influenzae at only 10(-5) the efficiency of homologous DNA, but they competed for H. influenzae transformation as well as or better than homospecific DNA. The data indicated that in some of the species sharing the common ecological habitat of the mammalian respiratory tract, sequences necessary for competition and efficient uptake into H. influenzae are present in large numbers in their DNAs, which nevertheless have little overall homology with H. influenzae DNA.