• Journal of Microbiology and Biotechnology
• /
• v.23 no.11
• /
• pp.1577-1585
• /
• 2013

Bioethanol production from lignocellulose is considered as a sustainable biofuel supply. However, the low cellulose hydrolysis efficiency limits the cellulosic ethanol production. The cellulase is strongly inhibited by the major end product cellobiose, which can be relieved by the addition of ${\beta}$-glucosidase. In this study, three ${\beta}$-glucosidases from different organisms were respectively expressed in Saccharomyces cerevisiae and the ${\beta}$-glucosidase from Saccharomycopsis fibuligera showed the best activity (5.2 U/ml). The recombinant strain with S. fibuligera ${\beta}$-glucosidase could metabolize cellobiose with a specific growth rate similar to the control strain in glucose. This recombinant strain showed higher hydrolysis efficiency in the cellulose simultaneous saccharification and fermentation, when using the Trichoderma reesei cellulase, which is short of the ${\beta}$-glucosidase activity. The final ethanol concentration was 110% (using Avicel) and 89% (using acid-pretreated corncob) higher than the control strain. These results demonstrated the effect of ${\beta}$-glucosidase secretion in the recombinant S. cerevisiae for enhancing cellulosic ethanol conversion.

• Molecules and Cells
• /
• v.28 no.4
• /
• pp.369-373
• /
• 2009

Heterologous secretory expression of endoglucanase E (Clostridium thermocellum) and ${\beta}$-glucosidase 1 (Saccharomycopsis fibuligera) was achieved in Saccharomyces cerevisiae fermentation cultures as an ${\alpha}$-mating factor signal peptide fusion, based on the native enzyme coding sequence. Ethanol production depends on simultaneous saccharification of cellulose to glucose and fermentation of glucose to ethanol by a recombinant yeast strain as a microbial biocatalyst. Recombinant yeast strain expressing endoglucanase and ${\beta}$-glucosidase was able to produce ethanol from ${\beta}$-glucan, CMC and acid swollen cellulose. This indicates that the resultant yeast strain of this study acts efficiently as a whole cell biocatalyst.

• Microbiology and Biotechnology Letters
• /
• v.7 no.2
• /
• pp.91-95
• /
• 1979

Ethanol and Xylose were produced from cellulosic agricultural waste such as rice straw and corn cob by a single-step simultaneous hydrolysis-fermentation process utilizing semi-solid culture of Trithoderma as enzyme source and Saccharomyces yeast. By this process all the hexoses prduoced by the enzyme were converted to ethanol leaving pentoses which are not fermented by the yeast. By processing 50 g of rice straw, 18 ml of ethanol and 2.7 g of xylose were produced and 50 g corn cob produced 3.8 ml of ethanol and 10.8 g of xylose. Alkali-treatment of rice straw showed little effects on the productivities of ethanol and xylose. The possible reasons are discussed.

• 한국신재생에너지학회:학술대회논문집
• /
• 2011.05a
• /
• pp.179.1-179.1
• /
• 2011

Pretreatment of cellulosic biomass is necessary before enzymatic saccharification and fermentation. The objective of this study was to evaluate the effect of combined aqueous ammonia-dilute sulfuric acid treatment on cellulosic biomass. Miscanthus was pretreated using aqueous ammonia and dilute sulfuric acid solution under high temperature and pressure conditions to be converted into bioethanol. Aqueous ammonia treatment was performed with 15 %(w/w) ammonia solution at $150^{\circ}C$ of reaction temperature and 20 minutes of reaction time. And then, dilute sulfuric acid treatment was performed with 1.0 %(w/w) sulfuric acid solution at $150^{\circ}C$ of reaction temperature and 10 minutes of reaction time. The compositional variations of this combined aqueous ammonia-dilute sulfuric acid treatment resulted in 68.0 % of cellulose recovery and 95.7 % of hemicellulose, 81.3 % of lignin, 89.1 % of ash removal respectively. The enzymatic digestibility of 90.5 % was recorded in the combined pretreated Miscanthus sample and it was 14.7 times higher than the untreated sample. The ethanol yield in the Simultaneous Saccharification and Fermentation was 90.4 % of maximum theoretical yield based on cellulose content of the combined pretreated sample and it was about 98 % compared to the ${\alpha}$-cellulose ethanol yield.

• Journal of Microbiology and Biotechnology
• /
• v.32 no.1
• /
• pp.117-125
• /
• 2022

Until recently, four types of cellobiose-fermenting Saccharomyces cerevisiae strains have been developed by introduction of a cellobiose metabolic pathway based on either intracellular β-glucosidase (GH1-1) or cellobiose phosphorylase (CBP), along with either an energy-consuming active cellodextrin transporter (CDT-1) or a non-energy-consuming passive cellodextrin facilitator (CDT-2). In this study, the ethanol production performance of two cellobiose-fermenting S. cerevisiae strains expressing mutant CDT-2 (N306I) with GH1-1 or CBP were compared with two cellobiose-fermenting S. cerevisiae strains expressing mutant CDT-1 (F213L) with GH1-1 or CBP in the simultaneous saccharification and fermentation (SSF) of cellulose under various conditions. It was found that, regardless of the SSF conditions, the phosphorolytic cellobiose-fermenting S. cerevisiae expressing mutant CDT-2 with CBP showed the best ethanol production among the four strains. In addition, during SSF contaminated by lactic acid bacteria, the phosphorolytic cellobiose-fermenting S. cerevisiae expressing mutant CDT-2 with CBP showed the highest ethanol production and the lowest lactate formation compared with those of other strains, such as the hydrolytic cellobiose-fermenting S. cerevisiae expressing mutant CDT-1 with GH1-1, and the glucose-fermenting S. cerevisiae with extracellular β-glucosidase. These results suggest that the cellobiose-fermenting yeast strain exhibiting low energy consumption can enhance the efficiency of the SSF of cellulosic biomass.

• Journal of Microbiology and Biotechnology
• /
• v.30 no.12
• /
• pp.1944-1949
• /
• 2020

Mutant sugar transporter ScGAL2-N376F was overexpressed in Kluyveromyces marxianus for efficient utilization of xylose, which is one of the main components of cellulosic biomass. K. marxianus ScGal2_N376F, the ScGAL2-N376F-overexpressing strain, exhibited 47.04 g/l of xylose consumption and 26.55 g/l of xylitol production, as compared to the parental strain (24.68 g/l and 7.03 g/l, respectively) when xylose was used as the sole carbon source. When a mixture of glucose and xylose was used as the carbon source, xylose consumption and xylitol production rates were improved by 195% and 360%, respectively, by K. marxianus ScGal2_N376F. Moreover, the glucose consumption rate was improved by 27% as compared to that in the parental strain. Overexpression of both wild-type ScGAL2 and mutant ScGAL2-N376F showed 48% and 52% enhanced sugar consumption and ethanol production rates, respectively, when a mixture of glucose and galactose was used as the carbon source, which is the main component of marine biomass. As shown in this study, ScGAL2-N376F overexpression can be applied for the efficient production of biofuels or biochemicals from cellulosic or marine biomass.

• Carbon letters
• /
• v.17 no.1
• /
• pp.1-10
• /
• 2016

Lignocellulosic biomass conversion to biofuels such as ethanol and other value-added bio-products including activated carbons has attracted much attention. The development of an efficient, cost-effective, and eco-friendly pretreatment process is a major challenge in lignocellulosic biomass to biofuel conversion. Although several modern pretreatment technologies have been introduced, few promising technologies have been reported. Microwave irradiation or microwave-assisted methods (physical and chemical) for pretreatment (disintegration) of biomass have been gaining popularity over the last few years owing to their high heating efficiency, lower energy requirements, and easy operation. Acid and alkali pretreatments assisted by microwave heating meanwhile have been widely used for different types of lignocellulosic biomass conversion. Additional advantages of microwave-based pretreatments include faster treatment time, selective processing, instantaneous control, and acceleration of the reaction rate. The present review provides insights into the current research and advantages of using microwave-assisted pretreatment technologies for the conversion of lignocellulosic biomass to fermentable sugars in the process of cellulosic ethanol production.

• KSBB Journal
• /
• v.7 no.1
• /
• pp.27-31
• /
• 1992

Xylose represents a major component of cellulosic materials. This paper describes patterns of ethanol fermentation by Saccharomyces cerevisiae from xylulose, which is an isomer of xylose. Special emphasis was placed on the effects of xylulose concentration and growth temperature on cell growth and ethanol yield. The maximum specific growth of $0.087 1/hr^{-1}$ was obtained at an initial xylulose concentration of 5 g/1. The ethanol yield was propotional to initial xylulose concentrations. A xylulose concentration of 16 g/l resulted in the maximum ethanol yield of 0.49 g EtOH/g xylulose, which corresponds to 90% of a theoretical value. It is interesting to nota that xylulose metabolism was accelerated by the presence of glucose as a carbon source.

• KSBB Journal
• /
• v.31 no.1
• /
• pp.73-78
• /
• 2016

The aim of this study attempted to verify the possibility of bioethanol production using wasted medium density fiberboard (wMDF). In order to produce bioethanol from wood cellulosic materials must be carried out the process of pretreatment, saccharification, fermentation and distillation. First, the wMDF was pretreated using sodium chlorite and pretreated wMDF was prepared to 8% slurry and then slurry was saccharified with the commercial enzyme (Cellic CTec3). The fermentable sugar and pH of saccharified substrate were about 5.5% glucose and 4.4, respectively. Herein we compared the results of ethanol yield according to the nutrients added or without addition to increase ethanol yield. Ethanol fermentation was finished in about 24 hours, but it was delayed in experimental group without nutrients. Ethanol content and fermentation ratio of the final fermented mash prepared by utilizing jar fermenter was 25.40 g/L and 86.64%, respectively. At this time, the maximum ethanol productivity was confirmed as 1.78 g/Lh (ethanol content 21.38 g/L, 12 h), and the overall ethanol productivity was 1.05 g/Lh (ethanol content 25.27 g/L, 24 h). Using fermented liquid we could produced bioethanol 95.37% by continuous distillator packed with copper element in laboratory scale. These results show that wMDF has a potential valuable for bioethanol production.

• Journal of Life Science
• /
• v.29 no.1
• /
• pp.135-145
• /
• 2019

Zymomonas mobilis has been recognized as a potential industrial ethanologen for many decades due to its outstanding fermentation characteristics, including high ethanol tolerance, fast sugar uptake rate, and high theoretical ethanol yield. With the emergence of the postgenomic era and the recent announcement of DuPont's world largest cellulosic ethanol production process, research on this bacterium has become even more important to harness successful application not only for use in the bioethanol process but also in other biochemical processes, which can be included in bio-refinery. As an important industrial microorganism, Z. mobilis will likely be exposed to various stressful environments, such as toxic chemicals, including the end-product ethanol and fermentative inhibitory compounds (e.g., furan derivatives, organic acids, and lignin derivatives in pretreatment steps), as well as physical stresses, such as high temperature during large-scale ethanol fermentation. This review focuses on recent information related to the industrial robustness of this bacterium and strain development to improve the ethanol yield and productivity in the lignocellulosic ethanol process. Although several excellent review articles on the strain development of this bacterium have been published, this review aims to fill gaps in the literature by highlighting recent advances in physiological understanding of this bacterium that may aid strain developments and improve the ethanol productivity for lignocellulosic biomass.