Infection of Competent Mycobacterium smegmatis with Deoxyribonucleic Acid Extracted from Bacteriophage B1

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Abstract
A relatively competent state of M. smegmatis for infection with DNA extracted from phage Bl was found in the late log phase of bacterial growth. This state of the culture was used in quantitatives studies on the infectivity of the DNA. The buoyant density of Bl DNA was 1.728 g/cc in CsCl, and 1[mu]g of the DNA produced 84 infective centers, the phage equivalent of which was 1.5 X 10-8. The infectivity was destroyed by catalytic amounts of DNase but not by specific Bl antiserum. Tween 80, which prevents phage adsorption did not prevent DNA infection. The response of plaque-forming ability to DNA concentration suggested that 2 or more molecules are required to initiate an infective center. The low efficiency of DNA infection in mycobacteria was considered to be caused by a limiting population of competent cells in the culture employed; in this experiment less than 10-5 of the cells were infected with DNA. A typical cycle of infection was observed, although the latent period was prolonged and the burst size reduced after DNA infection. The transition of Bl DNA infection to DNase insensitivity had a lag period of about 10 min., and increased linearly with a velocity of about 0.24 infective centers per min. per [mu]g of DNA. Half of the infective titer was inactivated by heating at 92 C for 15 min. The melting temperature was about 96 C. Species barriers were not crossed by Bl DNA; however, the DNA was infectious for a B1-resistant mutant of the host.