Giant cells of Escherichia coli: a morphological study.

Bacterial growth without division was observed in a giant cell-producing strain of Escherichia coli K-12. Giant cell production is controlled by the lon(-) (failure of cell division after irradiation) and mon(-) (formation of irregularly shaped cells) genes. Irradiation of a lon(-)mon(-) strain (P678-A(4)) with low doses of ultraviolet or ionizing radiation results in the production of large, amorphous giant cells with 500 to 1,000 times the volume of the nonirradiated parents. The concentration of NaCl in the growth medium was found to influence irradiated-cell morphology. Low concentrations (0.2% NaCl) resulted in elongated cells, whereas spherical giant cells were produced in the presence of high salt (1% NaCl) concentrations.Thin-section electron microscopy revealed an extensive network of intracellular membranes forming vacuoles, vesicles, and cisternae. These structures bear a striking resemblance to the rough and smooth membranes (endoplasmic reticulum, Golgi complex, vacuoles, etc.) found in eucaryotic cells.