Ethanol from cellulose and cellobiose of woody-substrates in a single stage of 3-combined-bioprocesses employing a non-GM yeast cell-factory

Abstract

The present study aims to prepare a Saccharomyces cerevisiae cell factory, to combine three bioprocesses in a single stage, including cellulolytic enzyme production, cellulose hydrolysis to glucose, and fermentation with low cost of nutrients to ethanol, without any genetic modification. Cell factories are prepared, in which S. cerevisiae cells are covered with starch gel (SG), either containing Trichoderma reesei (SG-T. reesei), or cellulase produced from T. reesei (SG-cellulase). The work comprises the cellulose bioconversion using S. cerevisiae/SG-cellulase, and S. cerevisiae/SG-T. reesei to carry out alcoholic fermentation in one batch with low nutrient cost. In addition, the effect of different concentrations of yeast in the cell factory on fermentation rate was examined. SEM, FTIR spectra analysis and cellulose fermentation were used to prove the successful preparation of cell factory and its activity to ferment cellulose in one combined bioprocess. The cellulose sourced from delignified sawdust was characterized with XRD spectra and porosimetry analysis. Cell factory models of S. cerevisiae/SG-T. reesei and S. cerevisiae/SG-cellulase were able to ferment cellulose from wood, obtaining 32% and 62% ethanol production yield, respectively. S. cerevisiae/SG-T. reesei and S. cerevisiae/SG-cellulase resulted to 4.07 and 7.30 mL ethanol/L, respectively. The final glucose concentration was very low (0–0.07 g glucose/L). It is also concluded that the increase of S. cerevisiae concentration in CF helped an improvement in the bioconversion process.