Basic aspects of radiation action on microorganisms. Progress report, April 1, 1974--March 31, 1975

of other phenomena. We find no evidence of induced radioresistance in two lambda lysogens of E. coli. There IS induced radioresistance if the lysogens are of induction-minus phage. UV given at -79/sup 0/C, which is believed to produce DNA-protein crosslinks, is an excellent inducer and also a good mutagen. Near UV produces lesions which are recognized by the induced repair system. At the same time, near UV also damages the induced repair system. There is increased mutagenesis at 313 nm wavelength following induction by ionizing radiation. It is likely that the phenomenon of induced radioresistance can be produced in one of several nuclei and that this one can give rise to a resistant colony. We find no evidence of induced radioresistance, nor of inhibition of postirradiation DNA degradation, in two strains of Pseudomonas.