DNA as a solar dosimeter in the ocean

Area of Science:

• Marine Biology
• Photochemistry
• Environmental Science

Background:

• Stratospheric ozone depletion leads to increased solar UV-B radiation reaching ocean surface waters.
• UV-B radiation poses significant risks to marine organisms, primarily through DNA damage.
• Quantifying the effective depth and magnitude of UV-B induced DNA damage in marine environments is crucial.

Purpose of the Study:

• To quantify UV-B induced DNA damage (cyclobutane pyrimidine dimers) at various depths in tropical marine waters.
• To assess the efficacy of DNA molecules as biological dosimeters for UV-B radiation in the marine environment.
• To determine the attenuation rate of UV-B induced DNA damage with increasing water depth.

Main Methods:

• Exposure of labeled DNA and bacteriophage phi X174 DNA in quartz tubes at different depths in marine waters.
• Quantification of UV-B induced pyrimidine dimers in DNA using radiochromatography.
• Assay of bacteriophage DNA inactivation via plaque formation in Escherichia coli spheroplasts.

Main Results:

• Pyrimidine dimer induction in DNA was linear with exposure time but varied significantly with depth, showing exponential attenuation.
• DNA at 3 meters depth exhibited only 17% of the pyrimidine dimers found at the surface.
• Bacteriophage DNA showed a 96% reduction in infectivity at the surface after one day, with no effect observed at 3 meters depth.
• A 'surface-enhanced dose' was observed, with DNA damage at the actual surface exceeding extrapolated values from deeper measurements.

Conclusions:

• DNA dosimeters are sensitive, convenient, and cost-effective for monitoring biologically effective UV-B flux in marine ecosystems.
• Biochemical (dimers) and biological (phage inactivation) endpoints of DNA dosimeters accurately reflect UV-B exposure.
• DNA damage attenuates exponentially with water depth, with significant protection afforded even at shallow depths like 3 meters.