THE PROPHAGE OF SPβc2dcitK1, A DEFECTIVE SPECIALIZED TRANSDUCING PHAGE OF BACILLUS SUBTILIS

The defective specialized transducing phage SPβc2dcitK1 carries two known bacterial genes, kauA and citK, as well as SPβ phage markers including the heat-sensitive repressor allele, c2. Some phage genes (including essential ones) are missing. When SPβc2dcitK1 transduces SPβ-sensitive cells of Bacillus subtilis, the defective prophage is inserted into sites in the homologous bacterial DNA of the attSPβ-kauA-citK region of the recipient chromosome. During the growth of these transductants, occasional excisions occur that result in the loss of the phage genes and OI the heterogenotic state. These excisions increase greatly in frequency during growth at repressor-inactivating temperatures. The kinds of insertions and excisions seen suggest that a Campbell-type (CAMPBELL 1962) circular phage genome may occur transiently. If the transductants are superinfected by SPβc2 or by the clear-plaque mutant SPβc1, the resulting double lysogen can be heat induced to release high-frequency of-transduction (HFT) lysates for kauA and citK.