MUTANTS OF ESCHERICHIA COLI UNABLE TO BE LYSOGENIZED BY TEMPERATE BACTERIOPHAGE P2

From Escherichia coli C lysogenization defective (lyd) mutants have been isolated. They are unable to become lysogenic for phage P2, although able to be lysogenized by other temperate phages. The lyd mutants show several new properties, as compared to the original strain: (1) higher sensitivity to X-rays or UV light (but they reactivate normally UV-irradiated T1); (2) lower recombination frequencies in bacterial crosses; (3) lower transduction frequencies in P1-mediated transduction. The lyd mutation maps in proximity of the xan marker on the E. coli C chromosome. Crosses between P2-lysogenic donors and lyd recipients have shown that the lyd mutation is not a deletion of a prophage attachment site. No lyd (P2) recombinants could be recovered from such crosses. Spontaneous mutants overcoming lysogenization defectiveness (old) have been isolated from P2. They are able to lysogenize lyd cells. These mutants are homoimmune with P2. In mixed infection experiments with P2 and P2old, P2old does not help P2 in lysogenizing lyd mutants. The data suggest that the old+ gene of P2 inhibits lysogenization of lyd cells by making all infected lyd cells inviable and that the phenomenon does not depend on an abnormal immunity or on a failure in the process of attachment of the phage to the host chromosome. © 1969.