The adsorption of Bacillus subtiiis phage PBS1 was studied, and it was demonstrated that the primary adsorption site for this phage is the flagellum of B. subtilis. The capacity of flagella to function for motility may be lost without the loss of their capacity to adsorb the phage and permit infection. Deoxyribonucleic acid injection by the phage is inhibited by cyanide, suggesting the requirement for cellular energy in the infection process. Joys (9) and Frankel and Joys (7) recently suggested that the receptor site for phage PBS1 (16) is the flagellum of Bacillus subtilis. They correlated susceptibility to phage adsorption and infection with motility of the organism, and demonstrated that four flagella-less (fa-) mutants and one flagellated but nonmotile mutant (mot-) of B. subtilis do not adsorb PBS1. They concluded that functional flagella were required for phage adsorption. The extensive investigations of Meynell (11) and of Schade, Adler, and Ris (14) have shown that the chi phage of Salmonella also exhibits flagellotropic properties. Interest in this laboratory for the past several years has focused on the bacterial flagellum. For this reason, and because of the possible biological significance that phage adsorption on the bacterial flagellum might have, a more extensive investigation on the general properties of phage PBS1 was undertaken. MATERIALS AND METHODS Organisms and growth medium. B. subtilis strains SB19, SBI71, 168, and SC3, 4, 6, and 23 were used in these studies. SB19 is a streptomycin-resistant prototrophic derivative of 168. SB171 is afla-derivative of 168 (trp) obtained from E. Lederberg. Strains SC3, 4, 6, and 23 are paralyzed mutants of 168 whose flagella lack the long period helix (Martinez et al., submittedfor publication). The other flamutants used were from our collection. The medium used for

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A lysozyme-detergent procedure was developed for isolation of tau-particles from cells infected by gene-21 mutants of T4 bacteriophage. These particles have a sedimentation coefficient of 440 h 10 S. They contain less than 1% detectable nuclease-resistant DNA, are smaller (650 X 850 A) than normal bacteriophage heads (800 X 1100 A), and exhibit two major bands on 7.5% Na dodecyl sulfate-acrylamide gels. The more prominent band (55,000 daltons) corresponds to the uncleaved, major capsid polypeptide (P23); the other band (32,000 daltons) corresponds to the gene-22 product (P22). Temperatureshift experiments with cells infected with tsN8 (gene 21) mutants were used to study the fate of tau-particles accumulated under nonpermissive conditions. 50 Min after ts N8-infected cells were shifted from the nonpermissive (41.50) to the permissive (250) temperature, a phage burst occurred that was 75% of that observed with wild-type phage. However, in "pulse-chase" temperature-shift experiments, the radioactive tau-particle peak only slightly decreased (by 10-14%) by 50 min after the shift, whereas an increased amount of radioactivity (about four times as much as the tau-particle decrease) appeared in phage particles. The results suggest that at least two pools of head polypeptides coexist in cells infected with gene-21 mutants. One pool is composed of head subunits assembled into tau-particles, which are mostly aberrant structures; the second pool is composed of head subunits that are incorporated into mature phage when the gene-21 product becomes functional.