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Oxygen toxicity in Treponema pallidum: deoxyribonucleic acid single-stranded breakage induced by low doses of
Abstract:
The effect of hydrogen peroxide on Treponema pallidum was investigated. The in vitro loss of virulence (as measured by rabbit inoculation) of T. pallidum was accelerated by as low as 100 microM hydrogen peroxide in the complex maintenance medium used. Higher doses led to rapidly accelerated death with 500 microM hydrogen peroxide causing sterilization of the medium within 3 to 4 h. Since hydrogen peroxide is known to cause single-stranded breaks in DNA, the effect of hydrogen peroxide on the treponemal genome was examined. Extensive breakage was caused by 100 microM hydrogen peroxide as determined on alkaline sucrose gradients. A limit was reached at 250 microM and above. Single-stranded breaks could be demonstrated as early as 5-10 min after exposure to hydrogen peroxide when the treponemes were exposed to 250 microM hydrogen peroxide; accelerated death was evident by 2 h past exposure demonstrating that DNA breakage was preceding death. Treponemal death caused by penicillin did not result in DNA breakage. The repair-proficient bacterium Escherichia coli K-12 was compared with T. pallidum. It required 10-100 times more hydrogen peroxide to cause various levels of breakage. Escherichia coli K-12 rapidly repaired DNA breakage once hydrogen peroxide was removed by addition of catalase. Treponema pallidum, in comparison, showed little or no repair in vitro. Addition of catalase or dithiothreitol to the medium protected against all but a low level of breakage; this may reflect on the ability of catalase and reducing agents to protect T. pallidum against oxygen toxicity in vitro.
Insights
Hydrogen peroxide damages Treponema pallidum DNA, accelerating its death in vitro. This bacterium shows limited DNA repair capabilities compared to Escherichia coli.
Area of Science:
- Microbiology
- Molecular Biology
- Pathogen Research
Background:
- Treponema pallidum is the causative agent of syphilis.
- Hydrogen peroxide is a reactive oxygen species known to damage DNA.
- Understanding T. pallidum's susceptibility to oxidative stress is crucial for developing new treatment strategies.
Purpose of the Study:
- To investigate the in vitro effects of hydrogen peroxide on Treponema pallidum virulence and DNA.
- To compare the DNA damage and repair mechanisms of T. pallidum with a model bacterium, Escherichia coli K-12.
Main Methods:
- In vitro exposure of T. pallidum to varying concentrations of hydrogen peroxide.
- Assessment of T. pallidum virulence loss via rabbit inoculation.
- Analysis of treponemal genome integrity using alkaline sucrose gradients.
- Comparison with hydrogen peroxide exposure and DNA repair in Escherichia coli K-12.
Main Results:
- Hydrogen peroxide at concentrations as low as 100 microM accelerated T. pallidum virulence loss in vitro.
- Extensive single-stranded DNA breaks were observed in T. pallidum exposed to 100-250 microM hydrogen peroxide.
- DNA breakage preceded treponemal death, which was evident within 2 hours of exposure.
- T. pallidum exhibited significantly less DNA repair compared to Escherichia coli K-12.
Conclusions:
- Hydrogen peroxide induces significant DNA damage in Treponema pallidum, leading to rapid loss of virulence.
- Treponema pallidum possesses limited in vitro DNA repair mechanisms against oxidative damage.
- These findings highlight the susceptibility of T. pallidum to oxidative stress and suggest potential therapeutic targets.