The Genetic Control of Radiosensitivity in Pseudomonas aeruginosa

Abstract

Genetically controlled differences of radiation sensitivity were first demonstrated in Escherichia coli strain B (1, 2) by the isolation of a mutant having increased resistance to both ultraviolet and ionizing radiation, and it was suggested that E. coli B and the radioresistant mutant B/r differed at only one locus. Radiosensitive mutants of E. coli B have also been isolated (3, 4). The existence of genetic recombination systems in bacteria has made possible the analysis of the genetic basis of radioresistance and radiosensitivity. It has been shown (5) that the radiosensitive E. coli K12 strain AB 1886 differs from the parent strain by a single mutational step. The gene involved has been located between one of the loci for arginine biosynthesis and the locus for arabinose fermentation. A locus controlling radioresistance (RA) in E. coli K12 has been reported to be closely linked to the loci for lactose fermentation and resistance to bacteriophage T6 (6). Another locus in E. coli K12, lon, has been shown to control filament formation and sensitivity to radiation. This gene is probably located between the genes controlling lactose and galactose fermentation and near the locus controlling resistance to bacteriophage T6 (7, 8). Again, a radiosensitive strain of E. coli B, BnII, has been shown to be the result of a mutation which occurred at a locus closely linked to the locus for xylose fermentation and between it and the locus for streptomycin resistance (9). This gene, which has been called syn, shows general effects on growth and on protein and nucleic acid synthesis. In contrast to these reports, it has been shown (10) that radiosensitivity in E. coli K12 is under multigenic control and that some of the genes are probably located between the proline and histidine loci. It has been suggested that one of these may be the gene fil (11), which controls radiation resistance and filamlent formation in E. coli B. This gene has been located between the markers for galactose fermentation and the cluster of genes for tryptophan synthesis. Together, these experiments clearly show that radiation sensitivity is under