Abstract
Effects of pre-irradiation treatments on the ultraviolet-induced mutation frequency and survival were investigated in an avirulent strain (Jucho strain) of Mycobacterium avium.
Pre-irradiation incubation in phosphorus-deficient medium gave rise to an increase in sensitivity to ultraviolet irradation when this pre-treatment itself caused no viability damage. Post-irradiation incubation in a medium supplemented with phosphates did not recover the loss in viability caused by ultraviolet irradiation in the cells pre-incubated in phosphorus-deficient medium.The increase of ultraviolet sensitivity was compatible with the previous finding in that ultraviolet irradiation produced a significant liberation of radioactive phosphorus compounds during irradiation.
Pre-irradiation incubation of cells in phosphorus-deficient medium promoted a marked decline in ultraviolet-induced mutation frequency to streptomycin resistance, while it caused no decline in induced mutation frequency to isoniazid resistance. There was a marked discrepancy between the effects on these two mutations.
It is supposed that phenotypic expression of mutation to streptomycin resistance requires sufficient amount of some phosphorus compounds.
Pre-irradiation incubation in nitrogen-free medium also caused increase in ultraviolet sensitivty.
