Recovery of Escherichia coli K-12 from near-ultraviolet radiation-induced membrane damage

A wild-type Escherichia coli K-12 strain was irradiated with broad-band near-ultraviolet radiation and after holding at 370C for various times in a complex recovery medium, was assessed for viability on either complex or minimal medium containing a high inorganic salt content. A near UV radiation fluence was used which reduced the surviving fraction to approximately 10% when assessing for viability on the complex medium plates. Near UV radiation induced sensitivity to inorganic salt was observed which was largely recoverable by holding treated cells in a complex recovery medium. The majority of the recovery process occurred in the initial 2 h post-irradiation holding period. No inhibition of the recovery process was produced by adding chloramphenicol or penicillin G to the recovery medium, indicating that neither protein synthesis nor cell wall synthesis were required for recovery. However, by adding bacitracin, which inhibits membrane synthesis, to the recovery medium, the amount of recovery of irradiated cells from salt sensitivity was decreased. These results demonstrate that recovery from near UV radiation-induced salt sensitivity occurs, it is independent of cell growth and membrane synthesis may be required for recovery. (author)