Heat-inducible reactivation of UV-damaged bacteriophage lambda

Area of Science:

• Bacteriophage biology
• DNA repair mechanisms
• Microbial genetics

Background:

• UV-irradiated bacteriophage lambda survival is enhanced by the bacterial SOS response.
• The SOS response is a complex DNA repair system in bacteria.

Purpose of the Study:

• To investigate a novel heat-inducible phage reactivation mechanism.
• To determine if this heat-inducible repair is mutagenic.
• To elucidate the molecular pathways involved in heat-induced phage reactivation.

Main Methods:

• Irradiating bacteriophage lambda and infecting recipient bacteria.
• Subjecting infected bacteria to a temperature shift from 30°C to 47°C.
• Analyzing phage survival and bacterial mutations in various mutant strains (recA, lexA, umuC, rpoH, uvrA).
• Assessing the effect of chloramphenicol pretreatment on phage reactivation.

Main Results:

• A heat shock (30°C to 47°C) induced non-mutagenic reactivation of UV-irradiated phage lambda.
• This heat-inducible repair increased with the number of UV lesions in phage DNA.
• The process was independent of SOS response (recA, lexA, umuC) and heat shock (rpoH) response mutations.
• Reactivation was abolished in uvrA mutants, indicating a role for excision repair.
• Chloramphenicol pretreatment significantly enhanced phage reactivation.

Conclusions:

• Heat shock stimulates phage lambda excision repair of UV lesions.
• This heat-inducible repair pathway is distinct from the SOS response.
• Blocking protein synthesis potentiates heat-induced phage reactivation, suggesting a role for pre-existing repair factors.