RECOVERY FROM ULTRAVIOLET IRRADIATION IN ESCHERICHIA COLI

Abstract

E. coli, strain B, after u.-v. irradiation, may survive to develop colonies or not, depending on certain minor changes in their subsequent treatment. Changes in survival level by as much as a factor of 100 have been observed. Transitions from "single-hit" to "multiple-hit" survival curves are also found. This effect should be recognized and controlled if errors in radiation experiments and their interpretation are to be avoided. A study of the conditions for recovery from this "radiation sickness" gives further evidence for validity of a cell poison hypothesis. According to this hypothesis, the primary effect in the killing of strain B by u.-v. is the production of a poison within the cell. Under certain conditions this poison can be inactivated or removed and the cell remains viable. Under other conditions the poison selectively inhibits the mechanism of cell division and unbalance is created between division and growth, a filament or "snake" is produced, and the cell finally dies. The killing of strain B by X-rays and B/r by ultraviolet is due to a different mechanism as no snakes are produced and no recovery is observed.