초록
<P>Microalgae have attracted increasing attention as a potential feedstock for biofuel production. However, direct high-density ethanol production from microalgae is not commercially feasible due to the requirement for complex pre-treatments and insufficient enzymatic hydrolysis. In this study, we successfully developed a consolidated bioprocessing (CBP) system using recombinant <I>Saccharomyces cerevisiae</I> displaying synergistic cellulases/amylases on cell surfaces to overcome energy-conversion limitations. As <I>Chlamydomonas</I> sp. JSC4 can accumulate considerable amounts of carbohydrates and pigments (<I>i.e.</I>, lutein), performing four rounds of pigment extraction from wet microalgal biomass using acetone was found to significantly eliminate the need for biomass pre-treatment and increase commercial viability. The pigment-extracted JSC4 residues increased ethanol production by 10.7% and 31.6% compared to raw starch and whole JSC4 cells, respectively. The theoretical ethanol production mass and yield from 300 g L<SUP>−1</SUP> of JSC4 material were 73 g L<SUP>−1</SUP> and 64%, respectively, after fermentation for 72 h in the presence of amylase- and cellulase-displaying yeasts, which are dramatically higher than those reported previously. Life cycle assessment (LCA) further revealed that this CBP system has 2.7- to 10.7-fold lower total environmental impact compared to alternative ethanol production methods using microalgal biomass. 2.43 kg ethanol and additional products of 5 g lutein from 1 kg microalgal biomass significantly increased the total economic output to $60.875. Overall, this study successfully demonstrates a feasible cell-surface display fermentation system for use in direct high-density ethanol production from pigment-extracted microalgal material.</P><P>Graphic Abstract</P><P>This study attempts to optimize the use of microalgal biomass for direct high-density ethanol production instead of conventional pretreatments, combining with comprehensive evaluation of environmental impact by life cycle assessment (LCA).<BR/><IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c9gc02634g'/><BR/></P>