Loss of the capacity of UV-irradiated Escherichia coli B-r to grow T4D.

The capacity of UV-irradiated Escherichia coli B/r cells grown on glycerol to support the growth of phage T4 was determined at intervals during postirradiation incubation of the cells. During the first 30 min capacity was virtually unimpaired, but then a rapid decrease occurred, followed by a slow increase. The dose response curve for the minimum fraction of infective centers observed at the end of the decline phase followed that for the survival of B/r for doses up to 300 ergs/mm2. At higher doses the relative sensitivity of the minimum infective centers decreased. After a dose of 520 ergs/mm2 to B/r cells, phage T4 both adsorbed to them and injected its DNA normally, regardless of the time of postirradiation incubation. After infection, individual cells either supported no phage synthesis, or a nearly normal burst was produced. Phage growth appeared to occur only in those cells that could eventually form colonies. In those cells fated not to survive, there was essentially no synthesis of phage DNA, nor was phage-induced endonuclease activity observed. Since the UV dose used causes respiration to be turned off about an hour after irradiation, we suggest that for glycerol-grown cells the loss of capacity is associated with loss of respiratory activity. Under conditions where respiration is only slightly and transiently affected by UV, as in the case of glucose-grown cells, there results a smaller but significant loss of capacity. Capacity seems to be particularly sensitive to respiratory failure after UV, but in glucose-grown cells, where respiration is not turned off, capacity may be lost for other reasons.