title: Lethal and mutagenic effects of ion beams and γ-rays in Aspergillus oryzae.
abstract: 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 (12)C(5+) ion beams with an LET of 121keV/μm. The (12)C(5+) ion beams had a 3.6-times higher lethal effect than low-LET (0.2keV/μm) γ-rays. The mutagenic effect was evaluated by the frequency of selenate resistant mutants. (12)C(6+) ion beams with an LET of 86keV/μm were the most effective in inducing selenate resistance. The mutant frequency following exposure to (12)C(6+) ion beams increased with an increase in dose and reached 3.47×10(-3) at 700Gy. In the dose range from 0 to 700Gy, (12)C(5+) ion beams were the second most effective in inducing selenate resistance, the mutant frequency of which reached a maximum peak (1.67×10(-3)) at 400Gy. 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 (12)C(5+) ion beams and γ-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 >2bp was generally low, deletions >20bp were characteristic for (12)C(5+) ion beams. γ-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.
authors.affiliation: Soy Sauce Laboratory, Yamasa Corporation, Chiba, Japan. toyoshima@yamasa.com
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Toyoshima
authors.forename: Akemi
authors.initials: A
authors.lastname: Takahashi
authors.forename: Hisaki
authors.initials: H
authors.lastname: Tanaka
authors.forename: Jun
authors.initials: J
authors.lastname: Watanabe
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Mogi
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Yamazaki
authors.forename: Ryoko
authors.initials: R
authors.lastname: Hamada
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Iwashita
authors.forename: Katsuya
authors.initials: K
authors.lastname: Satoh
authors.forename: Issay
authors.initials: I
authors.lastname: Narumi
mesh_terms: D001236:Aspergillus oryzae / Q000528:radiation effects*; D002244:Carbon; D002470:Cell Survival / Q000528:radiation effects*; D005720:Gamma Rays; D020450:Heavy Ions; D018499:Linear Energy Transfer; D016296:Mutagenesis; D009154:Mutation; D059645:Mutation Rate; D011839:Radiation, Ionizing
chemical_list: D002244:Carbon