| 1. |
- Taherzadeh, Mohammad J, 1965-, et al.
(författare)
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Strategies for enhancing fermentative production of glycerol - A review
- 2002
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Ingår i: Enzyme and Microbial Technology. - 0141-0229 .- 1879-0909. ; 31:1-2, s. 53-66
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Forskningsöversikt (refereegranskat)abstract
- The present paper reviews the metabolic basis of different methods for fermentative glycerol production. The most important microbial production organism is the yeast Saccharomyces cerevisiae but other yeast species, as well as molds, algae, and bacteria are of potential interest for glycerol production. A large variety of methods have been applied to increase the fermentative glycerol yield. The first methods were based on physiological control, e.g. chemically induced overproduction of glycerol through NADH entrapment by the addition of chemical steering agents (such as bisulfite). More recently, genetic engineering of the glycolytic pathway has been used to improve production, involving modulated function of e.g. triose phosphate isomerase, phosphoglycerate mutase, PDC or alcohol dehydrogenase. Direct intervention in the glycerol pathway, such as overexpression of G3P dehydrogenase, has also been tried. The applied strategies can be divided into three principal groups; (a) deactivation or down-regulation of NADH oxidation sites alternative to G3P dehydrogenase, (b) increase of NADH generation or, (c) direct changes in the carbon flux to glycerol. (C) 2002 Published by Elsevier Science Inc.
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| 2. |
- Castan, A., et al.
(författare)
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Oxygen enriched air supply in Escherichia coli processes : production of biomass and recombinant human growth hormone
- 2002
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Ingår i: Enzyme and microbial technology. - 0141-0229 .- 1879-0909. ; 30:7, s. 847-854
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate the impact of high oxygen and carbon dioxide concentrations, Escherichia coli was grown in batch cultivations where the air supply was enriched with either oxygen or carbon dioxide. The effect of elevated concentrations of oxygen and carbon dioxide on stochiometric and kinetic constants was studied this way. The maximum growth rate was significantly reduced, the production of acetic acid and the biomass yield coefficient on glucose increased in cultures with carbon dioxide enriched air, compared to reference cultivations and cultivations with oxygen enriched air. The application of oxygen enriched air was studied in high cell density cultivations of Escherichia coli. Two production processes were chosen to investigate the impact of oxygen enrichment. Biomass concentration, specific growth rate, yield coefficient, respiration, mixed acid fermentation products and the product yield and quality for the recombinant product were investigated. First, a process for the production of biomass was investigated. Exponential growth could proceed for a longer time and higher growth rates could be maintained with oxygen enriched air supply. However, a higher specific oxygen consumption rate per glucose was measured after the start of the oxygen enrichment, indicating higher maintenance and consequently the growth rate and yield coefficient decreased drastically in the end of the process. Second, a process for the production of recombinant human growth hormone (rhGH) was investigated. Although the glucose feed rate and all medium components were doubled, the amount of produced biomass could only be increased by 77% when oxygen enriched air (40% oxygen) supply was applied. This was due to a decreased yield coefficient of biomass per glucose. The total amount of produced product was decreased by almost 50% compared to the control, although less proteolytically degraded variants were produced.
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| 3. |
- Christakopoulos, Paul, et al.
(författare)
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Direct conversion of straw to ethanol by Fusarium oxysporum : Effect of cellulose crystallinity
- 1991
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Ingår i: Enzyme and microbial technology. - 0141-0229 .- 1879-0909. ; 13:3, s. 272-274
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Tidskriftsartikel (refereegranskat)abstract
- Wheat straw was successfully fermented to ethanol by Fusarium oxysporum F3 in a one-step process. Cellulose crystallinity was found to be a major factor in the bioconversion process. Ethanol yields increased linearly with decreasing crystallinity index. Approximately 80% of straw carbohydrates were converted directly to ethanol with a yield of 0.28 g ethanol/g−1 of straw when the crystallinity index was reduced to 23.6%.
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| 4. |
- Christakopoulos, Paul, et al.
(författare)
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Direct fermentation of cellulose to ethanol by Fusarium oxysporum
- 1989
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Ingår i: Enzyme and microbial technology. - : Elsevier BV. - 0141-0229 .- 1879-0909. ; 11:4, s. 236-239
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Tidskriftsartikel (refereegranskat)abstract
- The cellulase hyperproducing strain F3 of Fusarium oxysporum fermented glucose, xylose, cellobiose, and cellulose directly to ethanol. Conversion of cellulose to ethanol was markedly affected by the pH of both aerated preculture and nonaerated fermentation. Optimum values of cellulose conversion to ethanol were obtained when aerated and nonaerated processes were carried out at pH 5.5 and 6, respectively. Maximum ethanol concentrations of 9.6 and 14.5 g l−1, corresponding to 89.2 and 53.2% of the theoretical yield, were obtained when the fungus was grown under nonaerated conditions at 34°C for 6 days in a medium containing 20 and 50 g l−1cellulose, respectively.
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| 5. |
- Ignatova, Z., et al.
(författare)
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The relative importance of intracellular proteolysis and transport on the yield of the periplasmic enzyme penicillin amidase in Escherichia coli
- 2000
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Ingår i: Enzyme and microbial technology. - 0141-0229 .- 1879-0909. ; 26:04-feb, s. 165-170
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Tidskriftsartikel (refereegranskat)abstract
- Intracellular proteolysis is an important mechanism for regulating the level of the periplasmic enzyme penicillin amidase in Escherichia coli. Evidence is presented that the active enzyme is localized in the periplasmic space and maturation of pro-enzyme occurs during transport through the cytoplasmic membrane or rapidly after its entrance in the periplasm. The rate constants of the transport through cytoplasmic membrane and of the intracellular proteolysis were estimated to be 0.01 h and 0.5 h, respectively. This indicates that more than 90% of the synthesized pre-pro-enzyme is lost by intracellular proteolysis occurring in the cytoplasm.
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| 6. |
- Prenosil, J E, et al.
(författare)
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Purine Alkaloid Producing Cell Cultures: Fundamental Aspects and Possible Applications in Biotechnology
- 1987
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Ingår i: Enzyme and microbial technology. - : Elsevier BV. - 0141-0229 .- 1879-0909. ; 9:8, s. 450-458
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Tidskriftsartikel (refereegranskat)abstract
- Coffea arabica is one of the plant species that has been widely studied with attention largely being given to its secondary products, caffeine and other purine alkaloids. The biosynthesis and significance of these alkaloids for the plant are elucidated and presented. Tissue cell culture and fundamental aspects of cell growth and alkaloid productivity are also discussed. The feasibility of Coffea cultivation in cell suspension has recently attracted the interest of many researchers. Although this cultivation is not of commercial interest, Coffea is especially suitable as a model cell line for reaction engineering studies because the purine alkaloids are well-characterised and readily released in culture medium. The use of free and immobilized coffee cells in various types of bioreactors (stirred tank, expanded bed, and membrane device) is shown.
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| 7. |
- Puchart, Vladimı́r, et al.
(författare)
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Production of xylanases, mannanases, and pectinases by the thermophilic fungus Thermomyces lanuginosus
- 1999
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Ingår i: Enzyme and microbial technology. - 0141-0229 .- 1879-0909. ; 24:5-6, s. 355-361
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Tidskriftsartikel (refereegranskat)abstract
- A group of 17 strains of the thermophilic fungus Thermomyces lanuginosus was examined for the production of xylanases, β-mannanases, arabinanases, and pectinases. All strains were found to be xylanolytic, and several were proven to be outstanding producers of microbial xylanase on glucuronoxylan and corn cobs. The strains hyperproducing xylanase secreted low amounts of xylan-debranching enzymes and did not produce β-mannan and arabinan-degrading enzyme systems. Only the strains showing lower xylanase production exhibited a higher degree of xylan utilization and also the ability to produce a mannanolytic enzyme system. One of the mannanolytic strains was found to be capable of producing arabinan-degrading enzymes. This strain also showed the best production of pectinolytic enzymes during growth on citrus pectin or sugar beet pulp. Some of the strains have good potential for use as sources of important industrial enzymes of high thermal stability.
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| 8. |
- Rozkov, A., et al.
(författare)
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Dynamics of proteolysis and its influence on the accumulation of intracellular recombinant proteins
- 2000
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Ingår i: Enzyme and microbial technology. - 0141-0229 .- 1879-0909. ; 27:10, s. 743-748
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Tidskriftsartikel (refereegranskat)abstract
- A method to quantify the impact of proteolysis on accumulation of recombinant proteins in E. coli is described. A much smaller intracellular concentration of staphylococcal protein A (SpA) (14.7 mg.g(-1)) compared to the fusion protein SpA-beta galactosidase (138 mg.g(-1)) is explained by a very high proteolysis rate constant of SpA. The SpA synthesis rate reached a maximum one hour after induction and gradually decreased to half of this value at the end of the cultivation. The decrease of the synthesis rate and the Ist order kinetics of proteolysis lead to an equilibrium between synthesis and degradation of SpA from 2 h after induction. This resulted in no further SpA accumulation in cells, though synthesis continued for at least 10 h. Similar experiments with recombinant protein ZZT2 also revealed that most of the synthesized product was degraded. The order of proteolysis kinetics depended on the concentration of the recombinant protein: at low concentrations both SpA and ZZT2 were degraded according to first order kinetics, while at high concentrations ZZT2 was degraded according to zero order kinetics. In a protease Clp mutant the degradation rate decreased and intracellular concentration of ZZT2 increased from 50 mg.g(-1) to 120 mg.g(-1). The measurements of proteolysis rate throughout the cultivation enabled calculation of a hypothetical accumulation of the product assuming complete stabilization. In this case the concentration would have increased from 50 to 280 mg.g(-1) in II h. Thus, this method reveals the potential to increase the productivity by eliminating proteolysis.
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| 9. |
- Topakas, Evangelos, et al.
(författare)
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Purification and characterization of a Fusarium oxysporum feruloyl esterase (FoFAE-I) catalysing transesterification of phenolic acid esters
- 2003
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Ingår i: Enzyme and microbial technology. - 0141-0229 .- 1879-0909. ; 33:5, s. 729-737
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Tidskriftsartikel (refereegranskat)abstract
- An extracellular feruloyl esterase (FoFAE-I) from the culture filtrates of Fusarium oxysporum F3 was purified to homogeneity by ion-exchange, hydrophobic interaction and gel filtration chromatographies. The protein corresponded to molecular mass and pI values of 31 kDa and 9.5, respectively. The enzyme was optimally active at pH 7.0 and 55 °C. The purified esterase was fully stable at pH 7.0–9.0 and temperature up to 30 °C. Determination of kcat/Km revealed that the enzyme hydrolysed methyl p-coumarate (MpCA) 4.5, 9, and 239 times more efficiently than methyl caffeate (MCA), methyl ferulate (MFA) and methyl sinapinate (MSA), respectively. The enzyme was active on substrates containing ferulic acid ester linked to the C-5 and C-2 linkages of arabinofuranose but showed preference for the ester at position 2. 4-Nitrophenyl-2-O-trans-feruloyl-α-l-arabinofuranoside (NPh-5-Fe-Araf) was hydrolysed 100 times more efficiently than 4-nitrophenyl-5-O-trans-feruloyl-α-l-arabinofuranoside (NPh-2-Fe-Araf). Ferulic acid (FA) was efficiently released from destarched wheat bran (DSWB) when the esterase was incubated together with xylanase from Sporotrichum thermophile (a maximum of 92% total ferulic acid released after 4 h incubation). FoFAE-I by itself could release FA but at a level almost five-fold lower than that obtained in the presence of xylanase. The potential of FAE-I for the synthesis of various phenolic acid esters was tested using as a reaction system a surfactantless microemulsions formed in ternary mixture consisting of n-hexane, 1-butanol and water.
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| 10. |
- Antonopoulou, Io, 1989-, et al.
(författare)
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Screening of novel feruloyl esterases from Talaromyces wortmannii for the development of efficient and sustainable syntheses of feruloyl derivatives
- 2019
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Ingår i: Enzyme and microbial technology. - : Elsevier. - 0141-0229 .- 1879-0909. ; 120, s. 124-135
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Tidskriftsartikel (refereegranskat)abstract
- The feruloyl esterases Fae125, Fae7262 and Fae68 from Talaromyces wortmannii were screened in 10 different solvent: buffer systems in terms of residual hydrolytic activity and of the ability for the transesterification of vinyl ferulate with prenol or L-arabinose. Among the tested enzymes, the acetyl xylan-related Fae125 belonging to the phylogenetic subfamily 5 showed highest yield and selectivity for both products in alkane: buffer systems (n-hexane or n-octane). Response surface methodology, based on a 5-level and 6-factor central composite design, revealed that the substrate molar ratio and the water content were the most significant variables for the bioconversion yield and selectivity. The effect of agitation, the possibility of DMSO addition and the increase of donor concentration were investigated. After optimization, competitive transesterification yields were obtained for prenyl ferulate (87.5-92.6%) and L-arabinose ferulate (56.2-61.7%) at reduced reaction times (≤ 24 h) resulting in good productivities (> 1 g/L/h, >300 kg product/kg FAE). The enzyme could be recycled for six consecutive cycles retaining 66.6% of the synthetic activity and 100% of the selectivity.
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