Bioconversion of Brown Algae Sargassum horneri into Ethanol by Simultaneous Saccharification and Fermentation by Mannitol-fermenting Saccharomyces cerevisiae

초록

Sargassum horneri is a sea-drifting brown macroalga often found along the coast of East Asian countries. It was recently found to be drifting from China toward Jeju Island in South Korea, causing damage to fisheries and vessels. Being considered as a marine waste, a huge amount of S. horneri was collected in the past 5 years, but an efficient and proper way to treat it has still not been found. Therefore, it is required to develop technologies to tackle this issue. Here, we conducted bioconversion of S. horneri by the yeast Saccharomyces cerevisiae in order to utilize it as a biomass source for producing ethanol. First, S. cerevisiae was engineered to extend its substrate range to mannitol, which is one of the major components of brown algae. Activation of the native HXT17 and MAN2 genes enabled the yeast to metabolize mannitol as the sole carbon source. Impact of pretreatment conditions, the type of hydrolytic enzymes, and biomass solid loadings on the ethanol production by the yeast were evaluated. The highest ethanol productivity was obtained when the biomass was pretreated at 121 o C and ethanol concentration was the highest when the biomass loading was 24% (w/v), giving the maximum concentrations of monosaccharides and ethanol of 47.29 g/ L and 22.94 g/L, respectively. The results obtained from this study suggest possible utilization of S. horneri as a raw material for cellulosic bioethanol production.

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