The two inducible responses, SOS and heat-shock, in Escherichia coli act synergistically during Weigle reactivation of the bacteriophage ϕX174

Abstract

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 ϕX174 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 ϕX174, 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 ϕX174 over normal Weigle reactivation; the enhancement being maximum when the cells were shifted from 30 – 47°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 ϕX174.