Response to bleomycin of Escherichia coli mutants deficient in DNA repair.

The effect of bleomycin on the colony forming ability of Escherichia coli K12 strains in exponential growth at 37 degrees C was not affected by introducing recA13, lexA1, polA1 and uvrA6 mutations. For cells starved for amino acids, wild type strains became ten-fold more resistant to bleomycin, but again introducing lexA1, polA1 and uvrA6 strains did not change the effect on colony forming ability; however, starved recA13 cells were now four-fold more sensitive. Strains with recA13, lexA1 and polA1 mutations were always more sensitive than wild type to gamma rays under the same conditions as used for the bleomycin treatment. It is suggested that bleomycin-induced lesions may be concentrated in that part of the bacterial genomes at the cell wall, near the replication forks.