• 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.

• Microbiology and Biotechnology Letters
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• v.26 no.4
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• pp.309-315
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• 1998

An extracellular levansucrase, which catalyzes the formation of levan from sucrose, from the culture broth of Zymomonas mobilis ZM1 was purified by conventional column purification methods. The final purification yield was 18.3 fold of the crude enzyme from Z. mobilis, with 16.5 % of the enzyme recovered in the preparation step. The molecular weight of the enzyme was estimated to be 91,000 by Superose 12 gel filtration, and 45,000 by SDS-PAGE, indicating that levansucrase is a dimer. The optimum pH for the enzyme activity was around pH 4.0 for sucrose hydrolysis, and was around pH 5.0 for levan formation. The enzyme was inhibited by some metal ions, such as Hg$\^$2+/ and Cu2$\^$2+/, and 50% of inhibition was observed with 5mM EDTA. The enzyme activity was enhanced by the presence of detergent Triton X-100, but inhibited by SDS completely The enzyme catalyzes the liberation of reducing sugars, oligosacccharides and the formation of fructose polymer(levan). The enzyme also catalyzes the transfructosylation reaction of fructose moiety from sucrose to various sugar acceptor molecules, including sugar alcohols.

• Applied Biological Chemistry
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• v.40 no.2
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• pp.89-94
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• 1997

In order to reduce energy input in direct ethanol production from raw starch by co-immobilized Aspergillus awamori(A) and Zymomonas mobilis(Z), A-Z 36 culture system which was changed to anaerobic after 36 h of aerobic fermentation without sterilization was investigated. This immobilized cell system can not be carried out under unsterile conditions because of growth of microbial contaminants from original medium. Among some food additives such as sorbic acid, benzoic acid, dehydroacetic acid, p-hydroxybenzoic acid, Vantocil IB and Neupectin-L, Vantocil IB and Neupectin-L were a potent antibacterial agent in A-Z 36 culture cell system and were not affected in hydrolysis of substrate as compared with the case of control. Ethanol yield(6.9 g/l) in system of addition of 0.1% Neupectin-L was slightly higher than that in control(6.4 g/l). When 2% starch was fed five times in fed-batch culture with 0.1% Neupectin-L, ethanol yield and productivity were 34 g/l and 2.0 g/l/day, respectively.

• KSBB Journal
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• v.5 no.4
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• pp.335-339
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• 1990

In order to develop economic processes for ethanol production from starch, a simultaneous saccharification and fermentation(SSF) process using Zymomonas mobilis and amyloglucosidase (AMG) was studied in semibatch modes using cell recycle. The cell recycle was carried out by adopting two different methods; microfiltration and settling. The cell recycle using microfiltration revealed higher productivity(5.4 g/l/h) than that using a settler(4.3 g/l/h). Taking the large-scale ethanol fermentation into account, the semibatch process using microfiltration system appeared most promising among others with respect to ethanol productivity, feasibility of scale-up and simplification of operation.

• 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 $0.2h^{-1}$.

• KSBB Journal
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• v.5 no.4
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• pp.329-334
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• 1990

In an attempt to develop a novel process for ethanol production from starch, a simultaneous saccharification and fermentation (SSF) process using Zymomonas mobilis and amyloglucosidase (AMG) was studied in continuous modes. Compared with a conventional cylindrical column type of fermentor, the tapered column type of fermentor was found to be superior in terms of reactor performance for ethanol fermentation. The tapered columm fermentor packed with coimmobilized Z. mobilis and AMG alleviated the problems which were associated with CO2 evolution and provided a significantly better flow pattern for both liquid and gas phases in the fermentor without channelling. However, the fluidized bed type of tapered column fermentor using flocculent strain of Z. mobiles and immobilized AMG showed lower productivity (5.2g/1/h) than that of packed bed type of tapered column fermentor(9.2g/l/h).

• KSBB Journal
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• v.11 no.1
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• pp.58-64
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• 1996

The purpose of this study is to develop a continuous process for sorbitol production using Zymomonas mobilis immobilized in K-carra-geenan. The glutaraldehyde cross-linking of toluene-treated cells immobilized in alginate or chitin showed high enzyme stability for long period. However, loss of enzyme activity was observed at 23% during 210h. In order to investigate the stability of glucose-fructose oxidoreductase of cethyltrimethylammoniumbromide (CT AB) treated cells, the long term continuous process was carried out with Z. mobilis immobilized in K-carrageenan in the continuous stirred tank reactor(CSTR) and the packed bed reactor. The continuous production of sorbitol with the immobilized CT AB permeabilized cells in packed bed reactor was more stable than in CSTR. Two stage continuous process with CT AB treated cells of Z. mobilis immobilized in K-carrageenan was carried out at various dilution rates. At the first stage, the productivity was increased up to 15 g/ $\ell$ -h as dilution rate increased and decreased over 0.32$h^{-1}$ of dilution rate. Similarly, maximum productivity obtained at the second stage was 22g/$\ell$ -h at 0.32$h^{-1}$

• Journal of Microbiology and Biotechnology
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• v.13 no.1
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• pp.90-98
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• 2003

In vivo $^31p$ Nuclear Magnetic Resonance ($^31p$NMR) and metabolic studies were carried out on an acetic acid tolerant mutant, Zymomonas mobilis $ZM4/Ac^R$, and compared to those of the parent strain, Z. mobilis ZM4, to evaluate possible mechanisms of acetic acid resistance. This investigation was initiated to determine whether or not the mutant strain might be used as a suitable recombinant host far ethanol production from lignocellulose hydrolysates containing various inhibitory compounds. $ZM4/Ac^R$ showed multiple resistance to other lignocellulosic toxic compounds such as syringaldehyde, furfural, hydroxymethyl furfural, vanillin, and vanillic acid. The mutant strain was resistant to higher concentrations of ethanol or lower pH in the presence of sodium acetate, compared to ZM4 which showed more additive inhibition. in vivo $^31p$ NMR studies revealed that intracellular acidification and de-energization were two mechanisms by which acetic acid exerted its inhibitory effect. For $ZM4/Ac^R$, the internal pH and the energy status were less affected by sodium acetate compared to the parent strain. This resistance to pH change and de-energization caused by acetic acid is a possible explanation for the development of resistance by this strain.

• Journal of Microbiology and Biotechnology
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• v.20 no.7
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• pp.1156-1162
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• 2010

During ethanol fermentation, bacterial strains may encounter various stresses, such as ethanol and acid shock, which adversely affect cell viability and the production of ethanol. Therefore, ethanologenic strains that tolerate abiotic stresses are highly desirable. Bacteria of the genus Deinococcus are extremely resistant to ionizing radiation, ultraviolet light, and desiccation, and therefore constitute an important pool of extreme resistance genes. The irrE gene encodes a general switch responsible for the extreme radioresistance of D. radiodurans. Here, we present evidence that IrrE, acting as a global regulator, confers high stress tolerance to a Zymomonas mobilis strain. Expression of the gene protected Z. mobilis cells against ethanol, acid, osmotic, and thermal shocks. It also markedly improved cell viability, the expression levels and enzyme activities of pyruvate decarboxylase and alcohol dehydrogenase, and the production of ethanol under both ethanol and acid stresses. These data suggest that irrE is a potentially promising gene for improving the abiotic stress tolerance of ethanologenic bacterial strains.

• Proceedings of the Microbiological Society of Korea Conference
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• 2005.05a
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• pp.206.3-206
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• 2005