Oxidation of phosphorothioate DNA modifications leads to lethal genomic instability

Area of Science:

• Microbiology
• Genetics
• Biochemistry

Background:

• Genomic modification with phosphorothioate (PT) sulfur is common in prokaryotes, including pathogens.
• PT sulfur's properties suggest roles in bacterial fitness during stress.

Purpose of the Study:

• To investigate the dynamic nature of PT DNA modifications.
• To determine the impact of oxidative stress on PT stability and bacterial genomic integrity.

Main Methods:

• Isotopic labeling and mass spectrometry to track sulfur replacement in PTs.
• Exposure of bacteria (Escherichia coli, Salmonella enterica) to hydrogen peroxide (H2O2) and hypochlorous acid (HOCl).
• Assessment of bacterial cytotoxicity and DNA strand breaks.

Main Results:

• PT sulfur replacement occurred at ~2% h-1 in unstressed bacteria.
• HOCl treatment increased PT turnover to 3.8-10% h-1, indicating sulfur damage and repair.
• PT-containing bacteria showed increased sensitivity to HOCl-induced cytotoxicity and DNA damage compared to H2O2.

Conclusions:

• PT DNA modifications are labile and contribute to genomic instability under oxidative stress.
• HOCl is a significant genotoxic agent for PT-containing bacteria, impacting their fitness.
• Findings suggest implications for bacterial competition and pathogenesis in environments with HOCl producers.