Effects of heavy ions on bacteria

Genetically well-known bacteria have been used to study efficiencies of heavy ions for mutation induction. For space experiments a technique of correlation of tracks of particles (in emulsion stacked on and between Petri dishes) with individual mutations, has been designed and checked in balloon flights. No clear cut results could be obtained without previous identification of genetic markers sensitive to irradiation by heavy ions. Accelerator experiments were performed at the Berkeley HILAC for systematic study. The results obtained on a strain of E. coli K12F- requiring threonine, leucine and arginine showed that the cell inactivation kinetics for gamma rays, helium, carbon and oxygen ions were almost identical (LD90 approaches 22krads) while argon was less effective (LD90 approaches 40 krads). Heavy ions up to oxygen were either equally or less efficient than gamma rays for induction of reverse mutations. Discrepancies between these findings and previous data on bacteria, yeast and Neurospora systems are discussed on the basis of radiosensitivity, ploidy, deletions, forward and reverse mutations.