Effect of Dark-repair Inhibitors on the Survival of Escherichia Coli B under Different Post-irradiation Conditions

Summary

The effect was followed of dark-repair inhibitors (5-bromouracil, caffeine and acriflavine) on the survival of E. coli B bacteria under different cultivation conditions after u.v.- and x-irradiation. Different cultivation conditions (temperature, medium) influence the extent of radiation damage. However, an increased survival of E. coli B bacteria at a raised cultivation temperature (44°c) and on minimal (M9) medium does not occur after incorporation of 5-BU into bacterial DNA. The radiosensitizing effect of 5-BU is characterized by sensitization factors at 50 per cent to 1 per cent survival levels, the values of which range in u.v.-irradiated bacteria between 3·0 and 2·2 (at 44°c) and 2·7 and 1·8 (on M9 medium) and between 1·8 and 1·6 (at 44°c) and 2·4 and 1·6 (on M9) in bacteria irradiated with x-rays. During post-irradiation cultivation on complete medium at 19° and 37°c the radiosensitizing effect either does not occur or occurs only to a slight extent. The corresponding sensitization factors for u.v.-irradiated bacteria range between 1·0 and 0·8 (19°c) and 1·0 and 1·2 (37°c); and between 1·2 and 1·3 (19°c) and 1·7 and 1·5 (37°c) for those irradiated with x-rays.

Post-irradiation cultivation in the presence of 0·3 per cent caffeine partially removes the increased survival on complete medium at 44°c, but has almost no effect on survival on this medium at 19° and 37°c. The presence of acriflavine in the medium decreases the survival of u.v.- and x-irradiated bacteria cultivated under all the post-irradiation conditions investigated.

The results show that the incorporation of 5-BU into DNA and the presence of caffeine in the culture medium inhibit the repair of the damaged mechanism of cell division which takes place during cultivation of irradiated bacteria on complete medium at 44°c and on minimal medium.