Abstract
High LET radiation such as accelerated heavy ions are considered to produce densely clustered DNA lesions unlike sparsely ionizing low LET radiation. We are interested in possible differences of mutational spectra reflecting the DNA lesion. Bacillus subtilis spores of strain HA101 with wild-type repair capacity were irradiated with C,Ar and Fe ions near the Bragg peak and gamma ray from Co60. From irradiated spores,172 (C=43, Ar=47, Fe=32, gamma=50)mutants exhibiting rifampicin resistance were isolated, and together with 47 spontaneous mutants, sequence changes in the rpoB gene were determined. More than three quarters of mutations were single-base substitution (SBS) distributed among 13 alleles. All the spontaneous mutations, except one three-base insertion, were SBS. Besides SBS, tandem-double substitutions, non-tandem double substitutions, in-frame insertions, and in-frame deletions were found. The proportions of these complex mutations and base substitutions targeted at GC pairs were higher among the mutations from the spores irradiated with Ar or Fe ions than those with C, gamma or spontaneous ones. The results indicate significant differences of DNA lesions produced by high LET ions in comparisons with low LET radiation.
