Abstract

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.