Dvelopment of coliphage N4: ultrastructural studies.

The basic properties of bacteriophage N4 development have been investigated in Escherichia coli Hfr 3300 under one-step growth and high cell density conditions. N4r(+) -infected bacteria are lysis inhibited in mass culture, burst asynchronously starting 180 min postinfection, and release over 3,000 phage per cell. During lysis inhibition the bacteria continuously elongate, increase in girth, and undergo characteristic morphological changes represented by the appearance of dark spots located at the cell poles. In thin sections, during the late stages of replication and assembly, the phage particles are localized exclusively in restricted areas of the cytoplasm near the polar regions. Large paracrystalline arrays of virions are found in over 7% of the cells before lysis. The most common mechanism of lysis consists in the formation of bulges located at random in the cell circumference; these burst and, without extensive disruption of the cell wall, the phage progeny escapes into the medium.