earticle

영어

Among marine biomass, red algae is mostly composed of cellulose and galactan. Galactan is a representative polymer consisting of D-galactose and anhydro-galactose. For efficient production of bioethanol from red algae, both glucose from cellulose and D-galactose from galactan should be fermented simultaneously. To increase galactose-consuming ability, in this study, four mutants of S. cerevisiae D452-2 were selected on a solid medium containing galactose and 2-deoxy-D-glucose (an analogue of glucose) after treatment of N-methyl-N'-nitro-N-nitroso-guanidine and cell enrichment. In batch fermentation using 50 g/L glucose and 50 g/L galactose, contrary to a similar pattern of glucose consumption among the wild and mutant strains, S. cerevisiae mutants (HJ7-13, 14, 52, 54) metabolized total galactose completely but the wild strain remained 34.8 g/L galactose in 40 hr of batch culture. As a result, S. cerevisiae HJ7-14 produced 42.9 g/L ethanol from 48.9 g/L glucose and 52.5 g/L galactose at 1.64 g/L-hr galactose consumption rate and 1.05 g/L-hr ethanol production rate, which were 3.3- and 1.7- fold higher than those of the wild strain. To elucidate the physiological properties of the mutant HJ7-14 strain, a series of batch cultures using galactose, glucose and ethanol, and analysis of gene expression in the galactose metabolism by real-time PCR were performed. The HJ7-14 mutant strain was less affected by glucose repression than the wild type. In presence of glucose, the GAL genes expression levels of HJ7-14 strain were almost 20 times higher than those of the wild type. However, the GAL genes of the wild type were also expressed well after glucose depletion. Physiological and transcriptional analyses suggested that the galactose metabolism of the HJ7-14 mutant strain was not significantly affected by glucose repression relative to the wild type strain.