Effect of radiation and freezing on [3H]DNA of Yersinia enterocolitica.

Freezing of the enteropathogenic bacterium Yersinia enterocolitica to -18 and -75 degrees C caused 7 and 42% cell death, respectively, and 0.329 and 0.588 single-strand breaks per 10(8) daltons of DNA, respectively, while radiation to one D10 dose (10% cell survival) combined with freezing to 2 to 0, -18, and -75 degrees C induced 0.05, 0.75, and 5.04 single-strand breaks, respectively. The increase in the effectiveness of radiation with respect to the yield of single-strand breaks at -18 and -75 degrees C is contrary to expectation and seems to be due to arrest of repair of single-strand breaks by these low temperatures.