Cofermentation of glucose and galactose by a newly isolated Saccharomyces cerevisiae strain in free and immobilized forms

• A yeast strain with a good performance on galactose fermentation was isolated.
• The immobilized yeasts are stable for several weeks without loss of ethanologenicity.
• The immobilized yeasts can tolerate up to 7–10% of ethanol for more than a month.
• The yeast strain is an efficient bioethanol producer using seaweed hydrolysate.

A newly isolated yeast strain from the soil of grape fruit farm was identified as Saccharomyces cerevisiae Wu-Y2 through molecular characterization. This strain, whether used in free or immobilized form, showed a good performance on co-fermentation of reagent grade mixed sugars comprising of glucose and galactose in production of bioethanol in batch and fed batch culture. The yield coefficient (YE/S; 0.47 g/g) for ethanol from monosaccharide and yield efficiency (YE; 92.0%) after 48 h fermentation of mixed sugars shown by this wild-type S. cerevisiae Wu-Y2 were much higher than those by engineered S. cerevisiae (D452-2BT) strain (0.34 g/g, 67%) and engineered industrial distillers’ yeast (0.28 g/g and 55%). The immobilized S. cerevisiae Wu-Y2 cells exhibited a high degree of operational stability for several weeks without significant loss of viability or ethanologenicity in fed batch culture and it can tolerate up to 7–10% of ethanol for more than a month. This strain also showed good ability to utilize glucose and galactose present in red seaweed hydrolysate with high ethanol conversion efficiency; it showed significant potential to be an efficient bioethanol producer using seaweed as a feedstock.