Marine Bacteria under Low-Intensity Radioactive Exposure: Model Experiments

Radioactive contaminants create problems all over world, involving marine ecosystems, with their ecological importance increasing in the future. The review focuses on bioeffects of a series of alpha and beta emitting radioisotopes (americium-241, uranium-(235 + 238), thorium-232, and tritium) and gamma radiation. Low-intensity exposures are under special consideration. Great attention has been paid to luminous marine bacteria as representatives of marine microorganisms and a conventional bioassay system. This bioassay uses bacterial bioluminescence intensity as the main testing physiological parameter; currently, it is widely applied due to its simplicity and sensitivity. Dependences of the bacterial luminescence response on the exposure time and irradiation intensity were reviewed, and applicability of hormetic or threshold models was discussed. A number of aspects of molecular intracellular processes under exposure to low-intensity radiation were analyzed: (a) changes in the rates of enzymatic processes in bacteria with the bioluminescent system of coupled enzymatic reactions of NADH:FMN-oxidoreductase and bacterial luciferase taken as an example; (b) consumption of an intracellular reducer, NADH; (c) active role of reactive oxygen species; (d) repairing of the DNA damage. The results presented confirm the function of humic substances as natural radioprotectors.

Automated summary

Radioactive contaminants pose problems globally, particularly in marine ecosystems, and their ecological significance is expected to increase in the future. This review focuses on the bioeffects of various alpha and beta emitting radioisotopes (americium-241, uranium-235/238, thorium-232, and tritium) and gamma radiation, with a special emphasis on low-intensity exposures. Luminous marine bacteria are highlighted as representative organisms, and their bioluminescence intensity is widely used as a simple and sensitive bioassay parameter. The review discusses the relationship between bacterial luminescence response and exposure time and irradiation intensity, and also explores molecular intracellular processes under low-intensity radiation, including changes in enzymatic processes, consumption of NADH, the role of reactive oxygen species, and DNA damage repair. The results demonstrate the natural radioprotective function of humic substances.