Ethanol production from Gracilaria fisheri using three marine epiphytic yeast species

Abstract

Biofuels, especially bioethanol, are renewable resources that can supplement fossil fuel use. Gracilaria fisheri is a major cultivated seaweed in Thailand and can be a potential source of bioethanol due to its high polysaccharide content. Marine yeasts collected from the surface of seaweed are poorly known, but could be a source of fermenting yeast when using seaweeds. We collected samples of G. fisheri cultivated in shrimp pond effluent from southern Thailand and isolated yeasts from their surface. Molecular methods (ITS2 sequence) were used to identify the species and ethanol production was measured using algal powder hydrolyzed with 1 M of H2SO4 as a substrate. These species (Candida parapsilosis, Candida glabrata, Kodamaea ohmeri) were identify and used in fermentation experiment. These three yeast species produced different amounts of ethanol (per gram sugars) with C. glabrata producing the highest amount (2.5 × 10−2 g ethanol g−1 sugars) and C. parapsilosis (1.70 × 10−2 g ethanol g−1 sugars) the lowest. This study revealed that epiphytic yeasts isolated from G. fisheri have potential for use in the production of ethanol.