Deuterated spores of Bacillus cereus were prepared using a multi-stage adaptation protocol and then preserved at -20, 4, 25 and 40°C, respectively, to investigate the genetic mutation effects of deuterium oxide (D2O) isotope. The effects of the D2O isotope on cell growth and sporulation, and spore heat resistance, survival and spontaneous mutation rate of spores were examined. The results suggested that B. cereus cells can be grown in a cultured medium containing 98% D2O, with no observed growth inhibitory effect. The improved heat resistance of the deuterated spores and the decreased sporulation rate were accompanied by an increase in the D2O concentration in the cultured medium. Although, the survival rate of spores reduced along with the extension of the preservation time, in contrast to spores cultured by H2O medium, the deuterated spores had higher survival rate at -20 and 40°C at storage, respectively. In general, the spontaneous mutation rate increased along with preservation temperature and time. The spontaneous mutation rate of the deuterated spores significantly decreased when compared with that of hydrogen culture (P<0.05). This result provided a preliminary experimental evidence to validate the Löwdin DNA mutation model based on the inter-base double proton transfer in a hydrogen pond of base pairs.
Key words: Deuterium oxide, Isotope effect, spontaneous mutation, proton-tunneling model.
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