• Journal of Life Science
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• v.14 no.3
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• pp.429-434
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• 2004

Levansucrase gene (levU) from Zymomonas mobilis was subcloned downstream of GALl promoter in pYES 2.0 and pYInu-AT [GALl0 promoter＋exoinulinase signal sequence of Kluyveromyces marxianus], resulting pYES-levU and pYInu-levU, respectively. The two expression plasmids were introduced into an invertase-deficient strain, Saccharomyces cerevisiae SEY2102, and then transformants showing high activity of levansucrase were selected. When each yeast transformants was cultivated in medium containing galactose, the extracellular and intracellular activities of levansucrase reached about 7.17 U/㎖ with the strain harboring pYES-levU and 6.61 U/㎖ with the strain harboring pYInu-levU. It was found that about 50% of levansucrase were detected in the medium and periplasmic space, and exoinulinase signal sequence didn't enhance the secretion efficiency. Furthermore, the recombinant levansucrase expressed in yeast seems to be produced as a hyper-glycosylated form.

• 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.

• Microbiology and Biotechnology Letters
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• v.13 no.3
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• pp.213-221
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• 1985

The effects of ginseng extract, crude saponin and ether layer fraction on the alcohol fermentation and the growth of Zymomonas mobilis studied. The growth of Zymomonas mobilis was inhibited by the addition of ginseng extract, crude saponin and ether layer fraction, of which the last was shown to have the most inhibitory effect. The pH cultural broth recorded a significant decrease during 36 hrs alcohol fermentation, followed by a slower decrease in pH after 36 hrs. The alcohol fermentation was stimulated most remarkably by the addition of 0.305％ crude saponin, while inhibited most by the addition of 0.228％ ether layer fraction.

• Journal of the Korean Society of Food Science and Nutrition
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• v.24 no.5
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• pp.803-810
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• 1995

Co-immobilized mixed culture system(A-Z system) composed of two different oxygen-demanding strains, aerobic(Aspergillus awamori) and anaerobic(Zymomonas mobilis) strains, in a Ca-alginate gel beads was developed to increase ethanol production from raw starch as a carbon source. Optimal mixture ratio of A. awamori and Z. mobilis was $1.25{\times}10^{9}\;spores/L-gel$ and 0.5g cells/L-gel, respectively. After 120 hours of cultivation, gel beads distinguished oxygen-rich surface for A. awamori from oxygen-deficient central part for Z. mobilis. At A-Z culture system, yield of ethanol on glucose, $Y_{p/s}=0.18$, was very low and there was high leakage of cells from surface of gel beads. At A-Z 36 cultrue system with changing silicon check valve for cotton plug at 36 hours in A-Z culture system, there was no cell leakage from gel beads, pH was maintained at around 4.3 during cultivation, and yield of ethanol on glucose, $Y_{p/s}=0.36$, showed 2 times higher than that of control culture system(cotton plug culture).

• Journal of Microbiology and Biotechnology
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• v.7 no.6
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• pp.438-440
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• 1997

A continuous fermentation system employing immobilized cells of Zymomonas mobilis and Saccharomyces cerevisiae was studied for the mass production of ethanol. Ethanol production by cells immobilized with Ca-alginate was better than those by cells immobilized with K-carrageenan. Maximum ethanol production employing a continuous system by cells immobilized with Ca-alginate was 77.5 $g.l^{-1}h^{-1}$ at a dilution rate of 1.85 $h^{-1}$ with 82% conversion rate for Z. mobilis while that was 40.2 $g.l^{-1}h^{-1}$ at a dilution rate of 0.92 $h^{-1}$ with 85% conversion rate for S. cerevisiae. These results suggest that Ca-alginate is a better cell immobilization matrix than K-carrageenan and that immobilized cells of Z. mobilis are more efficient than S. cerevisiae for ethanol production.

• KSBB Journal
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• v.5 no.3
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• pp.223-227
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• 1990

This study describes the sorbitol production with permeabilized cells of Zymomonas mobilis immobilized in Ca-alginate. Toluene treated cells lose glucose-fructose oxidoreductase activity due to leaking of enzyme from the cells. In order to prevent this leakage, the permeabilized cells were immobilized in alginate and chitin. No significant loss of enzyme activity was apparent during 210h operation in a continuous process. The productivity of the continuous process was estimated to be about 3.5g/l -h for sorbitol at dilution rate $0.2h^{-1}$.

• Microbiology and Biotechnology Letters
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• v.20 no.5
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• pp.588-596
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• 1992

The fermentation characteristics of ethanol production by the use of immobilized Zymomonas mobilis KCTC 1534 cells were investigated in terms of formation factors such as substrate and product concentration. In batch fermentation, the maximum values of specific ethanol productivity, specific substrate uptake rate, ethanol yield, and glucose conversion rate were $29.14g/{\ell}{\cdot}h$, $60.24g/{\ell}{\cdot}h$, 0.48g/g, and 98.4%, respectively, with 17% glucose medium, and its ethanol productivity was $2.91g/{\ell}{\cdot}h$ in the case of 25 hour fermentation time. Repeated batch fermentation was possible for 30 days with 2.24-$2.94g/{\ell}{\cdot}h$ ethanol productivity. In semicontinuous fermentation, the maximum ethanol productivity was shown to be $15.7g/{\ell}{\cdot}h$ at $0.36h^{-1}$ effective dilution rate with 17% glucose concentration. In this case, ethanol yield coefficient and glucose conversion rate were 0.39 g/g, 64.7%, respectively.

• Microbiology and Biotechnology Letters
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• v.16 no.5
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• pp.402-406
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• 1988

The aim of the presented paper was to elucidate the physiological background of ethanol inhibition on glucose uptake, ethanol production and cell growth in Z. mobilis. Data obtained from batch and continuous cultures showed that the rates of glucose uptake and ethanol production were not affected but growth rate was apparently reduced by ethanol produced. In order to know the effects of ethanol on the anabolism and the catabolism in Z. mobilis, enzyme activities of the Enter-Doudoroff pathway, viz. hexokinase, glucose 6-phosphate dehydrogenase, were analyzed with the cell grown at different concentration of ethanol produced. As results, it was found that the activities of the glucose kinase and the glucose 6-phosphate dehydrogenase were not affected greatly by the concentration of ethanol where the glucose uptake rates revealed a relatively constant value. However it was very interesting to note that transketolase, which is an essential enzyme to provide the important precursors for cell growth, was affected more apparently to reduce by increasing ethanol levels. Those results might suggest that the apparent reduction of growth rate at ethanol concentration above 20 g/$\ell$ would be caused by the reduction of the transketolase activity, which in turn provide less precursor for the cell growth.

• Journal of Industrial Technology
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• v.3
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• pp.33-38
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• 1983

The effect of various environmental conditions on the growth kinetics of Zymomonas mobilis were studied and the kinetic parameters were evaluated. The value of ${\mu}m$ was $0.45hr^{-1}$ and Ks was 0.23 g/L. Inhibition of growth at high glucose concentration was found to follow the threshold substrate inhibition. Threshold substrate concentration was 102 g/L and substrate inhibition constant was 196 g/L. The effects of yeast extract concentrations were found to follow the Monod equation. ${\mu}m$ value was $0.45hr^{-1}$ and Ks was 0.3 g/L at 20 g/L of glucose and $0.24hr^{-1}$ and 0.24 g/L respectively at 200 g/L of glucose. The optimum temperature was found to be $35^{\circ}C$ and the activation energy of growth was 7.7 Kcal/mole below $35^{\circ}C$ and -29 Kcal/mole above $35^{\circ}C$.

• KSBB Journal
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• v.8 no.1
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• pp.10-16
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• 1993

The use of Jerusalem artichoke containing $\beta$-1, 2-fructose oligomer for the production of D-sorbitol and L-sorbose has been studied. The employment of inulinase(0.398%, v/v) for the hydrolysis of 40% (v/w) Jerusalem artichoke juice resulted in 36.7g/1 of glucose and 85.3g/1 of fructose at $50^{\circ}C$. These sugars were utilized as substrates for D-sorbitol and L-sorbose production. Coimmobilization of inulinase and permeabilized cells of Zymomonas mobilis in the mixture of chitin (5%, w/e) and x-carrageenan(4%, w/v) resulted in the production of 30.2g/1 of D-sorbitol by using inulin as a substrate. The process of L-sorbose production from D-sorbitol by Gluconobacter suboxydans was optimized with respect to the substrate concentration, level of dissolved oxygen and glucosic and concentration. Gluconlc acid produced by Zymomonas mobilis from glucose was found to inhibit Gluconobacter suboxtans in conversion of D-sorbitol to L-sorbose. In view of removing such inhibitory effect by gluconic acid, mutants were selected by the NTG (N-methyl-N'-N'-nitro-N-nitrosoguanidlne) treated method. Mutants selected by NTG mutagenesis showed no inhibitory effects of gluconic acrid against L-sorbone production when its concentration increased up to 100g/1. A mutant produced 40.1g/l of L-sorbose in the medium containing 100g/l D-sorbitol and 100g/l-gluconic acid. This result is consider able when compared with L-sorbose concentration (21.7g/1) obtained from the fermentation with wild type strain of Gluconobacter suboxnians.