Effect of radiation and freezing on ( super(3)H)DNA of Yersinia enterocolitica

Freezing of the enteropathogenic bacterium Y. enterocolitica to -18 and -75 degree C caused 7 and 42% cell death, respectively, and 0.329 and 0.588 single-strand breaks per 10 super(8) daltons of DNA, repectively, while radiation to one D sub(10) dose (10% cell survival) combined with freezing to 2 to 0, -18, and -75 degree 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 degree C is contrary to expectation and seems to be due to arrest of repair of single-strand breaks by these low temperatures.