Effects of Americium-241 (241Am), alpha-emitting radionuclide of high specific radioactivity, and tritium (3H), beta-emitting radionuclide, on luminous bacteria Photobacterium phosphoreum were compared. Bioluminescence intensity served as a marker of bacterial physiological activity. Three successive stages in the bioluminescence response to 241Am and 3H were found under conditions of lowdose irradiation: (1) absence of effects, (2) activation, and (3) inhibition. They were interpreted in terms of bacterial response to stressfactor as stress recognition, adaptive response/syndrome, and suppression of physiological function (i.e. radiation toxicity). Times of bioluminescence activation (TBA) and inhibition (TBI) were suggested as parameters to characterize hormesis and toxic stages in a course of chronic low-dose irradiation of the microorganisms. Values of TBA and TBI of 241Am were shorter than those of 3H, revealing higher impact of alpha-irradiation (as compared to beta-irradiation) under comparable radiation doses. Increases of peroxide concentration and NADH oxidation rates in 241Am aquatic solutions were demonstrated; these were not found in tritiated water. The results reveal a biological role of reactive oxygen species generated in water solutions as secondary products of the radioactive decay. The study provides a scientific basis for elaboration of bioluminescence-based assay to monitor radiotoxicity of alpha- and beta-emitting radionuclides in aquatic solutions.

Luminous marine bacteria are widely used as a bioassay with luminescence intensity being a physiological parameter tested. The purpose of the study was to determine whether bacterial genetic alteration is responsible for bioluminescence kinetics change under low-dose radiation exposure. Alpha-emitting radionuclide 241Am and betaemitting radionuclide 3H were used as sources of low-dose ionizing radiation. Changes of bioluminescence kinetics of Photobacterium Phosphoreum in solutions of 241Am(NO3)3, 7 kBq/L, and tritiated water, 100 MBq/L, were studied; bioluminescence kinetics stages (absence of effect, activation, and inhibition) were determined. Bacterial suspension was sampled at different stages of the bioluminescent kinetics; the doses accumulated by the samples did not exceed 1 Gy, being close to a tentative limit of a low-dose interval. Sequence analysis of 16S ribosomal RNA gene did not reveal a mutagenic effect of low-dose alpha and beta radiation. Previous results on bacterial DNA exposed to lowdose gamma radiation (0.25 Gy) were analyzed and compared to those for alpha and beta irradiation. A conclusion was made that DNA mutations are not associated with bacterial bioluminescence activation and inhibition under the applied conditions of low-dose alpha, beta, and gamma radioactive exposure. To view all the submission files, including those not included in the PDF, click on the manuscript title on your EVISE Homepage, then click 'Download zip file'. Abbreviations:ROS -Reactive Oxygen Species HTO -tritiated water ABSTRACTLuminous marine bacteria are widely used as a bioassay with luminescence intensity being a physiological parameter tested. The purpose of the study was to determine whether bacterial genetic alteration is responsible for bioluminescence kinetics change under low-dose radiation exposure. Alpha-emitting radionuclide 241 Am and betaemitting radionuclide 3 H were used as sources of low-dose ionizing radiation. Changes of bioluminescence kinetics of Photobacterium Phosphoreum in solutions of 241 Am(NO 3 ) 3 , 7 kBq/L, and tritiated water, 100 MBq/L, were studied; bioluminescence kinetics stages (absence of effect, activation, and inhibition) were determined. Bacterial suspension was sampled at different stages of the bioluminescent kinetics; the doses accumulated by the samples did not exceed 1Gy, being close to a tentative limit of a low-dose interval. Sequence analysis of 16S ribosomal RNA gene did not reveal a mutagenic effect of low-dose alpha and beta radiation. Previous results on bacterial DNA exposed to low-dose gamma radiation (0.25 Gy) were analyzed and compared to those for alpha and beta irradiation. A conclusion was made that DNA mutations are not associated with bacterial bioluminescence activation and inhibition under the applied conditions of low-dose alpha, beta, and gamma radioactive exposure.

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