It is shown that the individual strands of bacteriophage T43 DNA are intact and that heat-denatured T03 DNA forms a bimodal distribution ina neutral CsCl density gradient. Recent reports have indicated that the denatured deoxyribonucleic acid (DNA) of several bacteriophages for Bacillus stearothermophilus forms two bands in a CsCl density gradient (2, 13, 15). The DNA in the two bands formed by TP-84 DNA was shown to be complementary, but the polynucleotide chains were not intact (13). The material in the two bands formed by
A bacteriophage (TO3) which infects the thermophilic bacterium Bacillus stearothermophilus ATCC 8005 was isolated and characterized. Infection of the bacterium by the bacteriophage was carried out at 60 C, the optimal growth temperature of the host. At 60 C, the phage had a latent period of 18 min and a burst size of about 200. The phage was comparatively thermostable in broth. The halflife of T43 was 400 min at 60 C, 120 min at 65 C, 40 min at 70 C, and 12 min at 75 C. The activation energy for the heat inactivation of T43 was 56,000 cal. The buoyant density of T403 in a cesium chloride density gradient was 1.526 g/ml. Electron micrographs of T43 indicate that the phage has a head that is 57 m,4 long. The dimensions and shape of the head are compatible with those of a regular icosahedron. Each edge of the head is 29 m,u long. The tail of T43 is 125 m,u long and 10 m,u wide. There are about 30 cross-striations that are spaced at 3.9-m, intervals along the tail. Under the conditions investigated, T43 adsorbed slowly to the host. Only 2.8 % of the phage adsorbed in 10 min at 60 C, the normal incubation temperature that was used. T43 was not infective to four other thermophilic strains or to two mesophilic strains of bacteria. There have been a number of reports dealing with bacteriophages for thermophilic bacteria
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