Production of ethanol from the mixture of beet molasses and cheese whey by a 2-deoxyglucose-resistant mutant ofKluyveromyces marxianus

Abstract

Fourteen lactose-fermenting strains of Kluyveromyces marxianus, including its anamorph, Candida kefyr, were grown in two media containing 20% (w/v) sugar as either beet molasses or cheese whey. Strain NBRC 1963 of K. marxianus converted sucrose and lactose to ethanol in both media most efficiently. However, ethanol was produced from sucrose and not from lactose by strain NBRC 1963 in the medium containing equal amounts of sugar from beet molasses and cheese whey. The spontaneous mutants resistant to 2-deoxyglucose in the minimal medium composed of galactose as the sole carbon source were isolated from strain NBRC 1963. Among them, strain KD-15 vigorously produced ethanol in the media containing beet molasses, cheese whey, or both. The mutant strain KD-15 was insensitive to catabolite repression, as shown by the observation that beta-galactosidase was not repressed in the presence of sucrose from beet molasses.