Formation and Ultrastructure of Extra Membranes in Escherichia coli

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A temperature-sensitive strain of Escherichia coli (strain 0111a1) was shown to accumulate membranous structures at 40 C. These “extra membranes” appeared as vesicles or whorls (or both), depending on the time of growth at 40 C. After 2 hr of growth at 40 C, only vesicles were observed in E. coli 0111a1 cells; both vesicles and whorls were apparent after 6 hr. The number of cells which contained both types of extra membrane reached a maximum value (75%) after 10 hr of growth at 40 C. Extra membrane production was also studied by using temperature shifts. In shift-up experiments, cells grown at 30 C into early stationary phase accumulated extra membrane after a shift to 40 C. The percentage of E. coli 0111a1 cells containing extra membrane decreased significantly after a shift from 40 to 30 C. Phase- and electron-microscopic observations indicated that E. coli 0111a1 cells grown at 40 C were larger than E. coli 0111: B4 cells grown at either temperature. The ratio of optical density per cell and cell measurements obtained from quantitative electron microscopy confirmed that E. coli 0111a1 cells grown at 40 C were about twice as large. Microdensitometer traces indicated that the dimension of a single membrane of either whorls or vesicles was 5.4 nm in peak-to-peak distance (8.8 nm total thickness).

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