Cellulosic ethanol: From revolutionary consolidated bioprocessing idea to proof of concept

W. H. Van Zyl, Riaan Den Haan, Shaunita H. Rose, Daniel C. La Grange, Ronel van Rooyen, John E. Mcbride, Lee R. Lynd, Marja Ilmen, Merja Penttilä

    Research output: Contribution to conferenceOther conference contributionScientific


    Four biological events occur during conversion of lignocellulose to ethanol via processes featuring enzymatic hydrolysis: production of glycosyl hydrolase enzymes (cellulases and hemicellulases), hydrolysis of the polysaccharides present in pretreated biomass, fermentation of hexose sugars, and fermentation of pentose sugars. Consolidation of these events in a single process step via a cellulolytic microorganism(s) is a promising approach to low-cost conversion of lignocellulose to fuels and chemicals. One strategy for developing a microorganism capable of such consolidated bioprocessing involves engineering the non-cellulolytic yeast Saccharomyces cerevisiae so that it expresses a heterologous cellulase system enabling crystalline cellulose utilization.

    We developed the fundamental principles behind consolidated bioprocessing as a microbial phenomenon and illustrated proof of concept in the laboratory through the successful expression of the three major cellulase activities (β‑glucosidase, β‑endo-glucanase and cellobiohydrolase) in S. cerevisiae. We have enabled this yeast to grow on cellobiose, amorphous cellulose (PASC) and crystalline cellulose (BMCC) through the combinational expression of a β‑glucosidase, endo-1,4-β-glucanase and cellobiohydrolase genes.

    Recently, as part of an international team funded by Mascoma Corporation in the USA, we accelerated the research effort and transferred appropriate genes to commercial yeast strains. Expression levels of CBH genes have been improved up to 2500-fold and collectively we could demonstrate with proprietary CBP-yeast strains efficient conversion of unwashed pretreated hardwoods to ethanol with a 2.5-fold reduction in cellulase loading at pilot scale, which represents a major reduction in operating costs for the commercial production of cellulosic ethanol. Conversion of 18% w/w waste paper sludge to ethanol was demonstrated with minimal external enzyme addition. These breakthroughs bring the application of CBP at commercial scale closer than anticipated as recent as a year ago.
    Original languageEnglish
    Publication statusPublished - 2010
    EventInternational Workshop on Wood Biorefinery and Tree Biotechnology - Örnsköldsvik, Sweden
    Duration: 21 Jun 201023 Jun 2010


    WorkshopInternational Workshop on Wood Biorefinery and Tree Biotechnology


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