Author(s)

Naoto Urano¹, Masami Ishida¹, Yuka Naito¹, Rintaro Endo¹, Toshinori Takei², Masachika Takashio², Masahiko Okai^1*

¹Laboratory of Marine Biochemistry, Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Tokyo, Japan.
²Zensho Laboratories of Food Technology, Zensho Holdings Co. Ltd., Tokyo, Japan.

Bioethanol is thought to be a renewable source of energy, because the biomasses used to make ethanol, such as sugar cane and its residual substance, molasses, are resources that can be continuously produced. But the practical use of ethanol to replace fossil fuels or atomic energy has been limited, because the production efficiencies of ethanol in relation to its substrates are not so high. Thus, for industrial production of the bioethanol, yeast fermentation would ideally be carried out in biomasses containing more highly concentrated carbohydrates. However, the environmental stresses in highly concentrated cultures might weaken the yeast’s physiological activities. From various kinds of aquatic yeast with stress tolerance, Torulaspora derbrueckii F2-11 and Wicherhamomyces anomalus AN2-64 were selected as candidates for high-sugar-tolerance yeasts as they showed remarkable growth in the YPD + sorbitol (600 g/L) medium at 25°C for 120 hrs. When the amounts and kinds of sugar alcohols in the cells of the two strains were measured in cultures containing 20 g/L or 400 g/L of D-glucose, maltose, or sucrose, the main two sugar alcohols that accumulated as the sugar concentration increased were glycerol and arabitol. Mutation by ethyl methanesulfonate of the parent strains T. derbrueckii F2-11 and W. anomalus AN2-64 induced mutants F2-11M or AN2-64M, which showed higher sugar, heat, and ethanol tolerances than their respective parents. Ethanol productivities and sugar assimilation activities of the mutants were also higher than those of the parents in the 25% (v/v) molasses.

Ethanol Fermentation, Stress Tolerance, Aquatic Yeast, Mutant, Ethyl

Urano, N. , Ishida, M. , Naito, Y. , Endo, R. , Takei, T. , Takashio, M. and Okai, M. (2021) Ethanol Fermentation by High-Stress-Tolerance Aquatic Yeasts and Their Mutants. Advances in Microbiology, 11, 616-629. doi: 10.4236/aim.2021.1111045.