Isolation of Aspergillus oryzae mutants producing low levels of 2,4,6-trichloroanisole

[摘要] Musty or moldy off-odor in sake severely reducesits quality. Such off-odor is caused by 2,4,6-trichloroanisole (TCA), a compound that is produced byAspergillus oryzae during sake production byO-methylating the precursor 2,4,6-trichlorophenol(TCP). TCP suppresses the growth of fungi, including A. oryzae, although TCA does not. Therefore,strains that are unable to convert TCP to TCAshould be sensitive to TCP in the medium. Nevertheless, A. oryzae with a disrupted O-methyltransferase gene (ΔomtT) grew in a medium containingTCP. In agar medium, we observed no growth difference between the ΔomtT strain and a non-disrupted transformant; however, a significant growthdelay was observed with the ΔomtT strain grown inliquid medium containing 0.5 µg/mL of TCP. Thisstrain was more sensitive to low concentrations ofTCP, suggesting that omtT contributes to the conversion (detoxification) of TCP in liquid culture. Wegenerated A. oryzae RIB 40 mutants by ultravioletirradiation and then cultured them in liquid mediumcontaining TCP to obtain strains that did not produce moldy odor. The slow-growing strains werecultured in agar plates and then used to make kojiwith added TCP. We obtained three strains withlower TCA-producing ability and with sufficienthydrolase activities for sake brewing.

[学科分类] 微生物学和免疫学

[关键词] Aspergillus oryzae;musty/moldy offodor;mutant;O-methyltransferase;2;4;6-trichloroanisole;2;4;6-trichlorophenol