Damage to the plasma membrane in Escherichia coli K-12 induced by far-ultraviolet radiation and its repair.

Escherichia coli cells treated with low fluences of far-uv radiation (up to 90 J/m2) showed repairable damage to the plasma membrane. The loss of the ability of the cells to exclude citrate was evident from the respiratory stimulation of irradiated cells when citrate was provided exogenously. This loss of a barrier was a result of a structural disorganization of the plasma membrane as seen by freeze-etching electron microscopy. Analysis of the plasma membrane proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed a characteristic loss of certain membrane proteins. When irradiated cells were incubated in glucose minimal medium at 37 degrees C for various times, a gradual recovery of membrane structure and function was observed. The recovery process was inhibited in the absence of an energy source as well as protein synthesis. The majority of the recovery occurred in the initial 1 h of the postirradiation holding. These results demonstrated that far-uv radiation at a fluence less than the D10 value had a direct or indirect effect on plasma membrane proteins, causing their release from the membrane bilayer. The lost proteins were subsequently regained by de novo protein synthesis.