Improvement of ethanol production from crystalline cellulose via optimizing cellulase ratios in cellulolytic Saccharomyces cerevisiae

Abstract

Crystalline cellulose is one of the major contributors to the recalcitrance of lignocellulose to degradation, necessitating high dosages of cellulase to digest, thereby impeding the economic feasibility of cellulosic biofuels. Several recombinant cellulolytic yeast strains have been developed to reduce the cost of enzyme addition, but few of these strains are able to efficiently degrade crystalline cellulose due to their low cellulolytic activities. Here, by combining the cellulase ratio optimization with a novel screening strategy, we successfully improved the cellulolytic activity of a Saccharomyces cerevisiae strain displaying four different synergistic cellulases on the cell surface. The optimized strain exhibited an ethanol yield from Avicel of 57% of the theoretical maximum, and a 60% increase of ethanol titer from rice straw. To our knowledge, this work is the first optimization of the degradation of crystalline cellulose by tuning the cellulase ratio in a cellulase cell-surface display system. This work provides key insights in engineering the cellulase cocktail in a consolidated bioprocessing yeast strain. Biotechnol. Bioeng. 2017;114: 1201-1207. © 2017 Wiley Periodicals, Inc.

Consolidated bioprocessing of corn cob-derived hemicellulose: engineered industrialSaccharomyces cerevisiaeas efficient whole cell biocatalysts

“…3A and 2A, same strain and inoculum quantity). Furthermore, it was observed that increasing the inoculum from 50 to 100 g wet cells/L, an inoculum concentration in the order of magnitude of the normally reported for CBP strains [8,36], improved the overall process ( Fig. 3A and 3B) and increased the ethanol titer from 8.15 to 11.1 g/L (corresponding to an increase of 36 % in ethanol concentration) and the ethanol yield from 0.240 to 0.328 g per g of potential sugar (Table 3).…”

The Role of Yeast-Surface-Display Techniques in Creating Biocatalysts for Consolidated BioProcessing

“…When the resulting strain was assessed by ethanol fermentation from 20 g/L PASC, it has successfully obtained 4.3 g/L ethanol in 72 h with an ESCY of~44% where the titer was about 1.7 times higher when compared to the strain not expressing the cellodextrin utilization pathway [68]. Another case where two exoglucanases from T. emersonii and C. lucknowense, a T. reesei endoglucanase (EG2), and an A. aculeatus β-glucosidase (BGL1) were co-displayed using the cocktail delta-integration strategy on the yeast surface by Liu, et al [69] in the attempt to obtain a highly cellulolytic strain. The transformants were then subjected to a high-throughput screening (HTS) methodology for the selection of the strain that exhibits high cellulolytic activity.…”

“…The transformants were then subjected to a high-throughput screening (HTS) methodology for the selection of the strain that exhibits high cellulolytic activity. The resulting strain that exhibits the highest cellulolytic activity was subjected to ethanol fermentation from Avicel (non-treated crystalline cellulose) and it obtained~3 g/L of ethanol within 96 h with an ESCY of~60% (highest reported ethanol yield for from avicel) [69].…”

The DNA‐methyltransferase inhibitor 5‐aza‐2‐deoxycytidine affects Humicola grisea enzyme activities and the glucose‐mediated gene repression

“…This pretreatment is necessary since most of the bacteria and yeast species do not present considerable cellulolytic activity at the industrial level. Efforts have been made in creating recombinant strains which are capable of hydrolyzing the biomass and fermenting the sugar monomers in an one‐step process . Filamentous fungi, such as Trichoderma reesei , Penicillium echinulatum , Aspergillus niger , and Humicola grisea are the main source of cellulases and hemicellulases genes for heterologous expression in Saccharomyces cerevisiae and Pichia pastoris .…”

“…biomass and fermenting the sugar monomers in an one-step process [3]. Filamentous fungi, such as Trichoderma reesei, Penicillium echinulatum, Aspergillus niger, and Humicola grisea are the main source of cellulases and hemicellulases genes for heterologous expression in Saccharomyces cerevisiae and Pichia pastoris [4].…”