The two inducible responses, SOS and heat-shock, in Escherichia coli act synergistically during Weigle reactivation of the bacteriophage phiX174.

PURPOSE

The objective of this study was to investigate how Escherichia coli cells responded at the level of DNA repair, when the cells were subjected to UV (ultraviolet) radiation and heat-stress to induce a DNA repair system (SOS) and heat-shock response, respectively.

MATERIALS AND METHODS

The experiments were performed to study the Weigle reactivation of the bacteriophage phiX174 in its host E. coli C/1 cells. Two distinct techniques, top layer agar plating and Western blotting, were employed to measure the plaque count of viable phages and to demonstrate the heat-shock response respectively.

RESULTS

Repair of UV-inactivated bacteriophages in UV-irradiated E. coli cells is known as Weigle reactivation. In the case of the single-stranded DNA containing bacteriophage phiX174, Weigle reactivation occurs only through the inducible SOS repair response. Here we report that when UV-irradiated E. coli cells were transferred to higher temperature, the consequent heat-shock enhanced the reactivation of UV-inactivated phiX174 over normal Weigle reactivation; the enhancement being maximum when the cells were shifted from 30 - 47 degrees C and incubated there for 30 min. The extent of increase of reactivation was less, when the cells were first subjected to heat-shock and then irradiated by UV. Besides heat, ethanol (5 - 10% volume/volume [v/v]), an established heat-shock inducer, also caused enhancement of phage reactivation and the maximum enhancement occurred at 8% v/v ethanol.

CONCLUSION

We suggest that the SOS and heat-shock responses in E. coli act synergistically in the reactivation of UV-damaged bacteriophage phiX174.