Lethal and mutagenic effects of ion beams and γ-rays in Aspergillus oryzae

Aspergillus oryzae is a fungus that is used widely in traditional Japanese fermentation industries. In this study, the lethal and mutagenic effects of different linear energy transfer (LET) radiation in freeze-dried conidia of A. oryzae were investigated. The lethal effect, which was evaluated by a 90% lethal dose, was dependent on the LET value of the ionizing radiation. The most lethal ionizing radiation among that tested was C-12(5+) ion beams with an LET of 121 keV/mu m. The C-12(5+) ion beams had a 3.6-times higher lethal effect than low-LET (0.2 keV/mu m) gamma-rays. The mutagenic effect was evaluated by the frequency of selenate resistant mutants. C-12(6+) ion beams with an LET of 86 keV/mu m were the most effective in inducing selenate resistance. The mutant frequency following exposure to C-12(6+) ion beams increased with an increase in dose and reached 3.47 x 10(-3) at 700 Gy. In the dose range from 0 to 700Gy, C-12(5+) ion beams were the second most effective in inducing selenate resistance, the mutant frequency of which reached a maximum peak (1.67 x 10(-3)) at 400 Gy. To elucidate the characteristics of mutation induced by ionizing radiation, mutations in the sulphate permease gene (sB) and ATP sulfurylase gene (sC) loci, the loss of function of which results in a selenate resistant phenotype, were compared between C-12(5+) ion beams and gamma-rays. We detected all types of transversions and transitions. For frameshifts, the frequency of a +1 frameshift was the highest in all cases. Although the incidence of deletions >2 bp was generally low, deletions >20 bp were characteristic for C-12(5+) ion beams. gamma-rays had a tendency to generate mutants carrying a multitude of mutations in the same locus. Both forms of radiation also induced genome-wide large-scale mutations including chromosome rearrangements and large deletions. These results provide new basic insights into the mutation breeding of A. oryzae using ionizing radiation. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.