Prevention of Repair in Irradiated Rhizopus stolonifer Sporangiospores by Inhibitors of Protein Synthesis

Chloramphenicol and certain other inhibitors of protein synthesis, if they are present during or immediately after irradiation, have sometimes reduced the lethal response of cells to irradiation (1-6). Other postirradiation treatments have similarly been reported to lessen the irradiation effect. These methods include holding in a non-nutrient suspension before plating (7-9); incubation at suboptimal (10, 11) or supraoptimal (12-14) temperatures; and inhibition of germination in dense suspensions in a nutrient medium (15). Kimball et al. (6) showed in Paramecium that caffein and iodoacetate, as well as protein inhibitors, also lessened radiation damage. They attributed the decrease in mutations to an increase of time for recovery without the stress of cell division. Somewhat similar conclusions were drawn by Alper and Gillies (4, 7) with Escherichia coli. Although chloramphenicol has been shown to enhance survival of cells after irradiation injury under certain conditions, it evidently can inhibit certain repair processes. Wolff (16) demonstrated that chromosome rejoining, after irradiation, is prevented by chloramphenicol. Further, chloramphenicol has sometimes increased the sensitivity of microorganisms to irradiation (17). Alper and Gillies (18) found that the survival of E. coli strain B was increased by chloramphenicol treatment only if it was used with a complete medium. If synthetic medium was used, cell viability decreased with time of incubation in contact with chloramphenicol. Sporangiospores of the fungus Rhizopus stolonifer (Ehrenb. ex Fr.) Lind. were inhibited from germinating when held in extremely dense suspensions, although other conditions were conducive to growth (15). Many spores that would have exhibited a lethal response if plated immediately after irradiation produced colonies on plating after germination had been delayed for 48 hours. Under these conditions, recovery was maximum at temperatures near optimum for growth. About twothirds of the recovery occurred during the first 24 hours, with but little additional recovery after 48 hours.