Changes in survival of Escherichia coli K-12 cells as a function of the medium in which they are X-irradiated: a rec and exr gene-dependent phenomenon.

Abstract

SummaryEscherichia coli K-12 wild-type cells suspended in growth medium during X-irradiation have a higher survival than cells irradiated in buffer, whether irradiated in air or nitrogen. To determine if this response was due to differences in radiochemistry during irradiation or to differences in the amount of repair, we studied the influence of the irradiation medium on the survival of several repair-deficient mutants (recA, recB, exrA, uvrB, polA1 and polA1 exrA) and on the repair of radiation-induced DNA single-strand breaks in a wild-type strain.Our studies showed that the effect of the irradiation medium on survival was dependent on the presence of functional recA, recB, and exrA genes. Sedimentation studies, however, did not show a difference in the final amount of repair of DNA single-strand breaks after X-irradiation in buffer or growth medium. Thus, the increased X-ray sensitivity resulting from irradiation in buffer appears to be due to the inhibition of some rec and exr gene-dependent repair p...