Bacteriophage Deoxyribonucleate Infection of Competent Bacillus subtilis1

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Reilly, Bernard E. (Western Reserve University, Cleveland, Ohio), and John Spizizen. Bacteriophage deoxyribonucleate infection of competent Bacillus subtilis. J. Bacteriol. 89:782–790. 1964.—Phenol extracts of the Bacillus subtilis bacteriophages φ1, φ25, and φ29 contained infectious deoxyribonucleic acid. The infectivity was destroyed by catalytic amounts of deoxyribonuclease but not by specific phage antiserum, ribonuclease, or trypsin. An infectivity of >106 infectious centers formed per μg of deoxyribonucleic acid (DNA) added was obtained. The stability of the infectious centers permitted an examination of a single cycle of phage replication in cells unable to adsorb the mature virus. A typical cycle was observed, although the latent period was increased and the burst size slightly reduced after DNA infection. The development of competence for bacterial transformation was strongly correlated with susceptibility to viral DNA infection. Both appeared and disappeared at the same phase of growth in the cell population. More than 4% of the viable cells in the competent population were infected by viral DNA. The kinetics of the transition of φ29 DNA infection to deoxyribonuclease insensitivity, and the relationship of infectivity to DNA dilution, were similar to the results obtained for bacterial transformation of a single marker. The doseresponse curve of φ1 and φ25 DNA was characteristic of that obtained in multiple transformation of unlinked genetic markers. Because of the low efficiency of infection, about 10−4 per phage equivalent of DNA added, it was not possible to prove that DNA alone was sufficient to initiate infection.

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