• Journal of the Korean Wood Science and Technology
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• 제39권6호
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• pp.490-497
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• 2011

본 연구는 옥살산으로 전처리를 수행한 후 얻어진 옥수숫대를 이용하여 동시당화발효를 위한 최적조건을 탐색하였다. Pichia stipitis CBS 6054를 이용한 동시당화발효에서 독립변수인 반응온도($25.8{\sim}34.2^{\circ}C$)와 교반속도(80~220 rpm)에 대한 에탄올 생산량은 각각 99% 신뢰구간을 가졌다. 종속변수로 에탄올 생산량을 적용하였을 때 $30^{\circ}C$, 170 rpm에서 최대의 에탄올 생산을 예측할 수 있었다(22.5 g/L). 최적의 온도 및 교반속도에서 최적 질소원을 조사한 결과 yeast extract (1.25 g/L)와 urea (1.25 g/L)를 혼합하여 사용하였을 경우 에탄올 생산량은 증가하였으며 trace metal 성분과 비타민은 첨가하지 않았을 때 에탄올 생산이 촉진되었다. 동시당화 발효를 위한 $KH_2PO_4$, $MgSO_4{\cdot}7H_2O$의 최적 농도는 각각 1 g/L, 0.25 g/L로 나타났다.

• 한국미생물·생명공학회지
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• 제27권2호
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• pp.145-152
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• 1999

Brettanomyces custersii CBS 5512 which has reported as a thermotolerant glucose-cellobiose co-fermentable yeast strain was mutated with UV and NTG to improve ethanol yield at higher than 4$0^{\circ}C$ B. custersii H1-23, H1-39, H1-55 and H1062 were finally selected for hyper-fermentable strains at higher than 4$0^{\circ}C$ from thermotolerant 7510 colonies through 5th selection. Among the selected strains, H1-39 mutant had better fermentability at 4$0^{\circ}C$ and 43$^{\circ}C$ from different concentrations of glucose. H1-39 and H1-23 mutants yielded more than 70% of the theoretical ethanol yield in 4 and 8% mixed sugars at above 4$0^{\circ}C$, which was 5-11% higher than those by original strain. Especially, H1-39 mutant had better fermentability in 4% mixed sugar. It showed 78.5% of the theoretical yield at 4$0^{\circ}C$ and 72.2% of the theoretical yield at 43$^{\circ}C$. On the other hand, theoretical yield of ethanol by H1-39 mutant in 8% mixed sugar at 4$0^{\circ}C$ and 43$^{\circ}C$ were 75.2% and 70.2%, respectively. Theses values increased up to 7-11% as compared to those by orginal strain. By the simultaneous saccharification and fermentation, ethanol production by H1-39 mutant increased up to more than 23% as compared to that by original strain.

• Journal of Microbiology and Biotechnology
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• 제27권9호
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• pp.1649-1656
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• 2017

In simultaneous saccharification and fermentation (SSF) for production of cellulosic biofuels, engineered Saccharomyces cerevisiae capable of fermenting cellobiose has provided several benefits, such as lower enzyme costs and faster fermentation rate compared with wild-type S. cerevisiae fermenting glucose. In this study, the effects of an alternative intracellular cellobiose utilization pathway-a phosphorolytic pathway based on a mutant cellodextrin transporter (CDT-1 (F213L)) and cellobiose phosphorylase (SdCBP)-was investigated by comparing with a hydrolytic pathway based on the same transporter and an intracellular ${\beta}$-glucosidase (GH1-1) for their SSF performances under various conditions. Whereas the phosphorolytic and hydrolytic cellobiose-fermenting S. cerevisiae strains performed similarly under the anoxic SSF conditions, the hydrolytic S. cerevisiae performed slightly better than the phosphorolytic S. cerevisiae under the microaerobic SSF conditions. Nonetheless, the phosphorolytic S. cerevisiae expressing the mutant CDT-1 showed better ethanol production than the glucose-fermenting S. cerevisiae with an extracellular ${\beta}$-glucosidase, regardless of SSF conditions. These results clearly prove that introduction of the intracellular cellobiose metabolic pathway into yeast can be effective on cellulosic ethanol production in SSF. They also demonstrate that enhancement of cellobiose transport activity in engineered yeast is the most important factor affecting the efficiency of SSF of cellulose.

• Journal of Microbiology and Biotechnology
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• 제32권1호
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• pp.117-125
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• 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
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• 제27권1호
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• pp.1-8
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• 2017

The production of high-value chemicals from natural resources as an alternative for petroleum-based products is currently expanding in parallel with biorefinery. The use of lignocellulosic biomass as raw material is promising to achieve economic and environmental sustainability. Filamentous fungi, particularly Aspergillus species, are already used industrially to produce organic acid as well as many enzymes. The production of lignocellulose-degrading enzymes opens the possibility for direct fungal fermentation towards organic acids such as itaconic acid (IA) and fumaric acid (FA). These acids have wide-range applications and potentially addressable markets as platform chemicals. However, current technologies for the production of these compounds are mostly based on submerged fermentation. This work showed the capacity of two Aspergillus species (A. terreus and A. oryzae) to yield both acids by solid-state fermentation and simultaneous saccharification and fermentation. FA was optimally produced at by A. oryzae in simultaneous saccharification and fermentation (0.54 mg/g wheat bran). The yield of 0.11 mg IA/g biomass by A. oryzae is the highest reported in the literature for simultaneous solid-state fermentation without sugar supplements.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2003년도 생물공학의 동향(XIII)
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• pp.460-460
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• 2003

• Journal of Microbiology and Biotechnology
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• 제11권4호
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• pp.598-606
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• 2001

A mathematical model is proposed that can depict the kinetics of simultaneous saccharification and fermentation (SSF) using steam-exploded wood(SEW) with a glucose- and cellobiose-fermenting yeast strain. Brettanomyces custersii. An expression to describe the reduction of the relative digestibility during the hydrolysis of the SEW is introduced in the hydrolysis model. The fermentation model also takes two new factors into account, that is, the effects of the inhibitory compounds present in the SEW hydrolysates on the microorganism and the fermenting ability of Brettanomyces custersii, which can use both glucose and cellobiose as carbon sources. The model equations were used to simulate the hydrolysis of the SEW, the fermentation of the SEW hydrolysates, and a batch SSF, and the results were compared with the experimental data. The model was found to be capable of representing ethanol production over a range of substrate concentrations. Accordingly, the limiting factors in ethanol production by SSF under the high concentration of the SEW were identified as the effect of inhibitory compounds present in the SEW, the enzyme deactivation, and a limitation in the digestibility based on the physical condition of the substrate.

• KSBB Journal
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• 제14권1호
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• pp.24-30
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• 1999

Brettanomyces custersli를 이용하여 신문지의 유가식 동시 당화발효에 의한 에탄올 생산에 대한 연구를 수행하였다. 유가식 동시당화발효에 의한 에탄올 생산을 효과적으로 수행하기 위한 초기 기질 투입 농도는 8%(w/v)이었고 효소의 비용을 감안한 최적 효소 농도는 cellulase의 경우 30EPU/g cellulase, $\beta$-glucosidase와 cellulase의 부피가 0.1(활성비 1.05)이었다. 앞에서 결정된 초기 조건들을 가지고 교반식 반응기에서 수행된 유가식 동시당화발효는 26.8g/L의 에탄올을 생산성에서 회분식 동시당화발효보다 약 2배의 값을 나타내었다.

• Journal of Microbiology and Biotechnology
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• 제19권10호
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• pp.1161-1168
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• 2009

Ethanol production by the simultaneous saccharification and fermentation (SSF) of low-value rice wine cake (RWC) without cooking was investigated. RWC is the filtered solid waste of fermented rice wine mash and contains 53% raw starch. For the SSF, the RWC slurry was mixed with the raw-starch-digesting enzyme of Rhizopus sp. and yeast, where the yeast strain was selected from 300 strains and identified as Saccharomyces cerevisiae KV25. The highest efficiency (94%) of ethanol production was achieved when the uncooked RWC slurry contained 23.03% starch. The optimal SSF conditions were determined as 1.125 units of the raw-starch-digesting enzyme per gram of RWC, a fermentation temperature of $30^{\circ}C$, slurry pH of 4.5, 36-h-old seeding culture, initial yeast cell number of $2{\times}10^7$ per ml of slurry, 17 mM of urea as the nitrogen additive, 0.25 mM of $Cu^{2+}$ as the metal ion additive, and a fermentation time of 90 h. Under these optimal conditions, the ethanol production resulting from the SSF of the uncooked RWC slurry was improved to 16.8% (v/v) from 15.1% (v/v) of pre-optimization.

• Journal of Microbiology and Biotechnology
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• 제19권8호
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• pp.845-850
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• 2009

Bioethanol derived from lignocellulosic biomass has the potential to replace gasoline. Cellulose is naturally recalcitrant to enzymatic attack, and it also surrounded by the matrix of xylan and lignin, which enhances the recalcitrance. Therefore, lignocellulosic materials must be pretreated to make the cellulose easily degraded into sugars and further fermented to ethanol. In this work, hydrothermal pretreatment on corn stover at $195^{\circ}C$ for 15 min with and without lower concentration of formic acid was compared in terms of sugar recoveries and ethanol fermentation. For pretreatment with formic acid, the overall glucan recovery was 89% and pretreatment without formic acid yielded the recovery of 94%. Compared with glucan, xylan was more sensitive to the pretreatment condition. The lowest xylan recovery of 55% was obtained after pretreatment with formic acid and the highest of 75% found following pretreatment without formic acid. Toxicity tests of liquor parts showed that there were no inhibitions found for both pretreatment conditions. After simultaneous saccharification and fermentation (SSF) of the pretreated corn stover with Baker's yeast, the highest ethanol yield of 76.5% of the theoretical was observed from corn stover pretreated at $195^{\circ}C$ for 15 min with formic acid.