• The Microorganisms and Industry
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• v.16 no.2
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• pp.53-57
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• 1990

본고에서는 이제까지 개발되어 현재 산업적으로 사용되고 있는 에탄올 생산공정을 살펴보고 scale-up의 사례로서 KIST 유전공학센터에서 Z.mobilis airlift 발효조에서 수행한 연구결과를 중심으로 에탄올 발효에 있어서 scale-up시 나타나는 문제점과 고려해야 할 제반사항에 대해 살펴 보기로 한다.

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

• Food Science and Biotechnology
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• v.16 no.3
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• pp.482-484
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• 2007

To investigate production and hydrolysis of levan, the levansucrase enzymes from Zymomonas mobilis ATCC 10988 and Rahnella aquatilis ATCC 33071 were used. The optimum temperature of R. aquatilis levansucrase for levan formation was $37^{\circ}C$, whereas that of Z. mobilis was $4^{\circ}C$, under the experimental conditions. Both levansucrases also catalyzed the reverse levan hydrolysis reaction. Levan hydrolysis reactions from both levansucrases were temperature dependent; high temperature ($20^{\circ}C$) was more favorable than low temperature ($4^{\circ}C$) by 4 times. Fructose was the only product from hydrolysis reaction by both levansucrases, showing that both levansucrases mediated the hydrolysis reaction of exo-enzyme acting. In both enzymes, initial levan hydrolysis activity was almost accounted to 1% of initial levan formation activity. The results allow the estimation of the fructose release rate in enzyme processing conditions.

• Mycobiology
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• v.32 no.4
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• pp.170-172
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• 2004

The efficiency of acid, enzyme and microbial pretreatment of rice bran was compared based on the content of cellulose, hemicellulose, reducing sugars and xylose in the substrate. An isolate of Aspergillus niger or a strain of Trichoderma viride(MTCC 800) was employed for microbial pretreatment of rice bran in solid state. Acid pretreatment resulted in the highest amount of reducing sugars followed by enzyme and microbial pretreatment. A. niger showed a higher rate of hydrolysis than T. viride. The rice bran hydrolysate obtained from the different methods was subsequently fermented to ethanol either by Zymomonas mobilis(NCIM 806) or by Pichia stipitis(NCIM 3497). P. stipitis fermentation resulted in higher ethanol(37% higher) and biomass production($76{\sim}83%$ higher) than those of Z. mobilis. Maximum ethanol production resulted at 12h in Zymomonas fermentation, while in Pichia fermentation, it was observed at 60h. Microbial pretreatment of rice bran by A. niger followed by fermentation employing P. stipitis was more efficient but slower than the other microbial pretreatment and fermentation.

• KSBB Journal
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• v.7 no.1
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• pp.15-20
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• 1992

The use of Jerusalem artichoke containing $\beta$-1, 2-fructose oligomer in the production of sorbitol that is used as food additives and precursor for the L-sorbose has been studied. Coimmobilization of both inulinase and oxidoreductase was considered for the simultaneous reaction for hydrolysis of inulin and conversion of glucose and fructose liberated from inulin to sorbitol. Both inulinase and oxidoreductase were immobilized in chitin(5%, w/v) and K-carrageenan(4%, w/v), The activity of oxidoreductase was specified by permeabilization of Zymomonas mobilis cell with 0.2% CTAB(Cetyltrimethylammonlumbromide). The use of inulinase for hydrolysis of inulin resulted in 36.65g/l of glucose and 85.32g/1 of fructose respectively. These are valuable substrates for sorbitol production. Using these hydrolyzates, accumulation of 35.64g/l for sorbitol occurred at $38^{\circ}C$ and pH6.2. When permeabilized cells and inulinase were coimmobilized, sorbitol produced at 30.15g/l although it is low compared with 35.64g/l in separated reactor system.

• Korean Journal of Microbiology
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• v.23 no.1
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• pp.56-63
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• 1985

We have characterized the plasmids of zymomonas, and constructed E. coli-Zymomonas shuttle vector. Plasmids have been detected in four strains of Zymomonas mobilis. All strains tested had at least one plasmid ranging in size from about 1.7 to 46kb. Antibiotics resistances of Z. mobilis were tested to select the host strain. All strains were very sensitive to tetracycline and chloramphenicol. Homology tests between the plasmids in four strains showed that the plasmids of ATCC10988 is highly homologous to those of ZM1, and that there is no homology between plasmids of ZM4 and Agll. The 1.7kb plasmid of ATCC10988, named as pZM886, also has no homology with plasmids of ZM4. A hybrid plasmid, designated to pBZ41, was constructed from pZM886 and pBR322. A restriction map of pBZ41 was established. Replicon of pZM886 didn't operate in E.coli and pBR322 seemed not to replicate in Zymomonas. pBZ41 was transfered from E. coli to Zymomonas by conjugal mobilization. The transconjugants were resistant to tetracycline and maintained pBZ41 stably.

• KSBB Journal
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• v.7 no.2
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• pp.144-148
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• 1992

The purpose of this study is to develop a continuous process for sorbitol production using dried Zymomonas mobilis immobilized in K-carrageenan. The methods of glularaldehyde cross-linking of enzymes in CTAB (celyltrimetylammoniumbromide) treated cells immobilized in K-carrageenan showed stability for the production of sorbitol for 30 days of operation. K-carrageenan beads entrapping permeabilized cells were dried to Improve bead rigidity and storage stability. A semi-batch process with dry beads was carried out and only a small loss of enzyme activity (less than 8%) was observed during 72h. The value of Vmax for the dry K-carrageenan beads was found to be one half or that for free cells. It was shown that the productivities of the continuous process with wet K-carrageenan beads and dry beads at a dilution rate 0.1h-1 were 3.4g/L-h and 2.88h/L-h, respectively.

• KSBB Journal
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• v.4 no.2
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• pp.110-117
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• 1989

The fiffusion characteristics of substrate of varing biomass concentrations into and from Ca- alginate gel beads in well-stirred solutions were investigated. Ca-alginate gel beads were immobilized by Zymomonas mobilis or free from cells. The values of the diffusion coefficient of substrate were calculated by means of the method of Least squares and Random pore model. Reaction rates are expressed by the Michaelis-Menten type equation, and the results are compared with experimental data. Intraparticle effective diffusivity of substrate resistance on reaction by using immobilized Z.mobilis entrapped by Ca-alginated gel seemed to be restricted by cell density. The experimental data also indicated relationship between the effective diffusivity and the cell concentration used in the gel preparation.

• Journal of Life Science
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• v.25 no.11
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• pp.1290-1297
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• 2015

Studies of the inactivation of a gene encoding pyruvate decarboxylase, pdc, in an ethanol-producing bacterium, Zymomonas mobilis, identified a mutant strain with 50% reduced PDC activity. To evaluate the possibility of a carbon-flux shift from an ethanol pathway toward higher value fermentation products, including pyruvate, succinate, and lactate, fermentation studies were carried out. Despite attempts to silence pdc expression in the wild-type strain ZM4 using cat-inserted pdc and pdc-deleted homologs by electroporation, the strain isolated showed partial gene activation. Fermentation experiments with the PDC mutant strain showed that the reduced expression level of PDC activity resulted in decreased rates of substrate uptake and ethanol production, together with increased pyruvate accumulation of 2.5 g l^-1 , although lactate and succinate concentrations were not significantly enhanced in these modified strains. Despite numerous attempts, no strains were isolated in which complete pdc inactivation occurred. This result indicates that the ethanol fermentation pathway of this bacterium is totally dependent on the activity of the PDC enzyme. To ensure a redox balance of intracellular NAD and NADH levels, other enzymes, such as lactate dehydrogenase for lactate, and enzymes involved in the production of succinic acid, such as pyruvate dehydrogenase (PDH) and malic enzymes, may be needed for their increased end-product production.