Seven mutants of Haemophilus influenzae were isolated by the criterion of sensitivity to ultraviolet (UV) inactivation of colony formation. These mutants and the wild type were characterized with regard to X-ray inactivation of colony formation, UV induction of division inhibition, the ability of the eight strains to act as recipients to UV-irradiated H. influenzae phage and transforming deoxyribonucleic acid (DNA), and the influence of acriflavine on the survival of UV-irradiated transforming DNA with these strains as recipients. The photoreactivable sector of transforming DNA with yeast photoreactivating enzyme was measured for the most UV-sensitive mutant and was found to be greater than that of wild type. Judged by the above criteria, the order of the strains' sensitivities shows some, but by no means complete, correlation from one type of sensitivity characterization to another, indicating that a minimum of two variables is needed to explain the differences in the strains. Acriflavine increases the UV sensitivity of transforming DNA except in the most sensitive mutant. This effect is usually, but not always, more pronounced in the case of the more UV-resistant marker. The acriflavine effect is postulated to be the result of at least two factors: (i) interference with repair of transforming DNA in the host cell, and (ii) interference with the probability of recombination between transforming DNA and host DNA.
The interaction between transformation and prophages of HPlcl, S2, and a defective phage of Haemophilus influenzae has been investigated by measurement of (i) the effect of prophage on transformation frequency and (ii) the effect of transformation on phage induction. The presence of any of the prophages does not appreciably alter transformation frequencies in various Rec+ and Recstrains. However, exposure of competent lysogens to transforming deoxyribonucleic acid (DNA) may induce phage but only in Rec+ strains, which are able to integrate transforming DNA into their genome. Transformation of Rec+ lysogens with DNA irradiated with ultraviolet (UV) light causes the production of even more phage than results from unirradiated DNA, but this indirect UV induction is not as effective as direct induction by UV irradiation of lysogens. Both types of UV induction are influenced by the repair capacity of the host. Wild-type cells contain a prophage and can be induced by transformation to produce a defective phage, which kills a small fraction of the cells. Defective phage in wild-type cells are also induced by H. parainfluenzae DNA, and a much larger fraction of the cells is killed. Strain BC200, which is highly transformable but is not inducible for defective phage, is not killed by H. parainfluenzae DNA, suggesting that wild-type cells are killed by this DNA because of phage induction. A minicellproducing mutant, LB1 1, has been isolated. Some phage induction occurs in this strain when the cells are made competent, unlike the wild type. A large majority of LB11 cells surviving the competence regime are killed by exposure to transforming DNA. When a transformable cell has been lysogenized, transformation frequencies may be altered. For example, lysoRgenic streptococci cannot be made highly competent, as measured by irreversible deoxyribonucleic acid (DNA) uptake (16), with the result that transformation frequencies are low relative to those of nonlysogenic cultures. Lysogenic Bacillus subtilis, on the other hand, retains its ability to be made competent (28) but shows decreased transformation (17, 29), although transfection is hardly affected and may even be increased (28).
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