Mycobacteria exploit three genetically distinct DNA double-strand break repair pathways

Area of Science:

• Molecular Biology
• Microbiology
• Genetics

Background:

• Bacterial pathogens employ DNA repair mechanisms to counteract host-induced genomic damage.
• DNA double-strand breaks (DSBs) pose a significant threat to bacterial survival.
• While Escherichia coli primarily uses homologous recombination (HR) for DSB repair, mycobacteria also utilize non-homologous end-joining (NHEJ).

Purpose of the Study:

• To investigate the DNA double-strand break (DSB) repair pathways in Mycobacterium smegmatis.
• To elucidate the roles of key proteins like RecBCD and AdnAB in these pathways.
• To understand the factors influencing pathway choice and resistance to DNA damaging agents.

Main Methods:

• Genetic analysis of Mycobacterium smegmatis mutants.
• Assessment of DNA repair pathway utilization (HR, NHEJ, SSA).
• Evaluation of resistance to ionizing radiation (IR) and oxidative DNA damage.

Main Results:

• Mycobacterium smegmatis possesses three DSB repair pathways: HR, NHEJ, and a novel single-strand annealing (SSA) mechanism.
• Inactivation of NHEJ or SSA is compensated by increased HR activity.
• RecBCD is essential for the RecA-independent SSA pathway, not HR, and does not confer IR resistance.
• AdnAB is crucial for the RecA-dependent HR pathway and confers significant resistance to IR and oxidative damage.

Conclusions:

• Mycobacterium smegmatis exhibits distinct DSB repair strategies compared to E. coli.
• The RecBCD and AdnAB helicase-nuclease machines are specifically dedicated to different DSB repair pathways.
• These findings highlight unique features of mycobacterial DNA repair, impacting pathogen survival and therapeutic strategies.