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The effect of D2O on the growth and transforming activities of Streptococcus pneumoniae
Abstract:
After an initial period of growth in medium made up in D2O, most strains of pneumococcus tested dramatically lost viability, the extent of the loss depending on the strain and on the amount of contaminating H2O in the D2O. This was followed by a recovery period. Once a strain was 'adapted', the ability to grow in D2O-medium without cell death was inherited, even after passage through H2O-medium, indicating the selection of mutants. Cultures that had not reached 'full adaptation' also exhibited cell death if transferred into either D2O-medium or H2O-medium, supporting the conclusion that the presence of hydrogen and deuterium together caused the toxicity. 'Adapted' cells exhibited an increased mutation frequency to a variety of antibiotic resistances, the propensity for this appearing in the death phase of 'adaptation'. The specific transforming activity of DNA preparations from cultures undergoing 'adaptation' decreased before DNA synthesis ceased indicating damage to the DNA. The integration efficiency of a low-efficiency marker also dropped during 'adaptation' before returning to the initial value when measured in a Hex- recipient, but remained constant in a Hex+ recipient, suggesting that the Hex system may be involved in repair of the DNA damage. 'Adapted' organisms showed evidence of possessing higher Hex activity and were also able to repair lesions caused by UV-irradiation better than the wild-type.
Insights
Heavy water (D2O) initially harmed pneumococcus viability, but adapted strains survived and showed increased mutation rates. This adaptation involved DNA repair mechanisms, suggesting deuterium toxicity triggers specific genetic changes.
Area of Science:
- Microbiology
- Genetics
- Biochemistry
Background:
- Deuterium oxide (D2O), or heavy water, has known biological effects.
- The impact of D2O on Streptococcus pneumoniae (pneumococcus) viability and adaptation is not fully understood.
Purpose of the Study:
- To investigate the effects of D2O on pneumococcus growth, viability, and genetic adaptation.
- To elucidate the mechanisms underlying D2O toxicity and bacterial adaptation.
Main Methods:
- Culturing pneumococcus strains in D2O-enriched media.
- Assessing bacterial viability and growth dynamics.
- Measuring mutation frequencies and antibiotic resistance.
- Analyzing DNA integrity and transforming activity.
- Investigating the role of the Hex system in DNA repair.
Main Results:
- Most pneumococcus strains initially lost viability in D2O, with recovery and adaptation observed.
- 'Adapted' strains exhibited inherited resistance to D2O toxicity and increased mutation frequencies.
- DNA damage was detected during adaptation, with evidence suggesting the Hex system's involvement in repair.
- 'Adapted' cells showed enhanced repair of UV-induced DNA lesions.
Conclusions:
- D2O toxicity in pneumococcus is linked to the combined presence of hydrogen and deuterium.
- Bacterial adaptation to D2O involves the selection of mutants with enhanced DNA repair capabilities, potentially mediated by the Hex system.
- The study highlights the intricate relationship between environmental stress, DNA damage, and bacterial evolution.