Spheroplast Formation in Cells of Escherichia coli Infected with a ∅X 174 Type Bacteriophage

Little is known about the intracellular changes in Escherichia coli infected with bacteriophage ∅X 174 (a tail-less phage with large capsomeres containing single-stranded DNA). Markert & Zillig (1965) found no detectable alteration in the structure of the cell wall in thin sections of lysing cells, the phage progeny being released by local ruptures in the cell envelope (cell wall/plasma membrane complex). The present communication describes a preliminary electron microscopic study of the lysis of E. coli c 2 by phage α 3 (Bradley, 1963), which is similar to ∅X 174 but has a wider host range. The results obtained show a completely different mechanism of lysis. Phage α 3 was grown to a high titre by the confluent lysis of host cells in nine double-agar-layer plates (diameter 15 cm.), which were then extracted with nutrient broth. The resulting suspension was used to infect a broth culture of E. coli c 2 (concentration 1 × 108 bacteria/ml.) at a multiplicity of 20 p.f.u. per bacterium.