Biotechnology and Bioengineering
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* Dữ liệu chỉ mang tính chất tham khảo
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Fermentative production of <scp>l</scp>‐glycerol 3‐phosphate utilizing a <i>Saccharomyces cerevisiae</i> strain with an engineered glycerol biosynthetic pathway Abstract Interest in l ‐glycerol 3‐phosphate (l ‐G3P) production via microbial fermentation is due to the compound's potential to replace the unstable substrate dihydroxyacetone phosphate (DHAP) in one‐pot enzymatic carbohydrate syntheses. A Saccharomyces cerevisiae strain with deletions in both genes encoding specific l ‐G3Pases (GPP1 and GPP2 ) and multicopy overexpression of l ‐glycerol 3‐phosphate dehydrogenase (GPD1 ) was studied via small‐scale (100 mL) batch fermentations under quasi‐anaerobic conditions. Intracellular accumulation of l ‐G3P reached extremely high levels (roughly 200 mM) but thereafter declined. Extracellular l ‐G3P was also detected and its concentration continuously increased throughout the fermentation, such that most of the total l ‐G3P was found outside the cells as fermentation concluded. Moreover, in spite of the complete elimination of specific l ‐G3Pase activity, the strain showed considerable glycerol formation suggesting unspecific dephosphorylation as a mechanism to relieve cells of intracellular l ‐G3P accumulation. Up‐scaling the process employed fed‐batch fermentation with repeated glucose feeding, plus an aerobic growth phase followed by an anaerobic product accumulation phase. This produced a final product titer of about 325 mg total l ‐G3P per liter of fermentation broth. Biotechnol. Bioeng. 2008;100: 497–505. © 2008 Wiley Periodicals, Inc.
Biotechnology and Bioengineering - Tập 100 Số 3 - Trang 497-505 - 2008
Alginate làm vật liệu cố định: I. Mối liên hệ giữa tính chất hoá học và vật lý của các hạt gel alginate Tóm tắt Các hạt gel alginate calci đã được chuẩn bị từ một loạt các alginate đã được đặc trưng tốt. Tính chất vật lý của các hạt phụ thuộc mạnh vào thành phần, cấu trúc tuần tự, và kích thước phân tử của các polymer. Các hạt với độ bền cơ học cao nhất, độ co ngót thấp nhất, độ ổn định tốt nhất đối với các cation đơn hóa trị, và độ xốp cao nhất được tạo ra từ alginate có hàm lượng axit L ‐guluronic cao hơn 70% và chiều dài trung bình của các khối G cao hơn 15. Đối với những alginate “g cao” này, độ nhớt nội tại tại điểm trùng lặp quan trọng đã được xác định, và đối với trọng lượng phân tử cao hơn 2,4 × 105 , độ bền của gel không phụ thuộc vào trọng lượng phân tử.
Biotechnology and Bioengineering - Tập 33 Số 1 - Trang 79-89 - 1989
#alginate #calcium alginate #gel beads #mechanical strength #porosity #monovalent cations #<jats:sc>L</jats:sc>‐guluronic acid #molecular weight #intrinsic viscosities #polymer
Hóa học tách chiết axit carboxylic sản phẩm lên men Tóm tắt Trong khuôn khổ một chương trình nhằm cải thiện công nghệ thu hồi chiết xuất các sản phẩm từ quá trình lên men hiện có, trạng thái hiện nay của công nghệ được xem xét một cách phê bình. Các axit được xem xét bao gồm axit propionic, axit lactic, axit pyruvic, axit succinic, axit fumaric, axit maleic, axit malic, axit itaconic, axit tartaric, axit citric, và axit isocitric, tất cả đều được thu nhận thông qua quá trình lên men aerôbic của glucose qua con đường glycolytic và bypass glyoxylate. Không có ngoại lệ nào, chính là axit đơn phân không phân ly được chiết vào các chất chiết xuất có khả năng tạo liên kết với oxy chuẩn và liên kết phốt pho. Trong pha hữu cơ, các axit này thường được dimer hóa. Quá trình chuyển tải chiết xuất tuân theo định luật Nernst, các hệ số phân tách đo được dao động từ khoảng 0.003 đối với hydrocacbon no đến khoảng 2 đến 3 đối với cồn aliphatic và ketone đến khoảng 10 hoặc lớn hơn đối với organophosphate. Các tỷ lệ phân phối cao tương tự cũng được đo khi sử dụng amin bậc ba chuỗi dài làm chất chiết xuất, hình thành các muối cồng kềnh ưu tiên hòa tan trong pha hữu cơ.
Biotechnology and Bioengineering - Tập 28 Số 2 - Trang 269-282 - 1986
#Axit carboxylic #Chiết xuất #Công nghệ #Lên men #Định luật Nernst #Axit đơn phân #Hydrocacbon #Cồn aliphatic #Ketone #Organophosphate #Amin bậc ba
Chitin/chitosan transformation by thermo‐mechano‐chemical treatment including characterization by enzymatic depolymerization Abstract Chitosan, the deacetylated derivative of chitin, was until recently produced by hydrolysis in 50% (w/v) NaOH. Application of thermo‐mechano‐chemical technology to chitin deacetylation was evaluated as an alternative method of chitosan production. This process consists of a cascade reactor unit operating under reduced alkaline conditions of 10% (w/v) NaOH. Prior mercerization of chitin at 4°C for 24 h was required for high deacetylation yields. Sudden decompression of the aqueous alkaline suspension of mercerized chitin resulted in near complete deacetylation of chitin. Reactor residence time was 90 s at 230°C prior to decompression. The chitosan produced was characterized by elemental analysis, 13 C–NMR and enzymatic depolymerization. Enzymatic determination of the degree of acetylation of chitin/chitosan mixtures was also investigated. Relative chitinase and/or chitosanase digestibilities were shown to be strongly dependent on chitin deacetylation. Based on enzymatic digestibilities, the alkaline aqueous high shear process does not appear to produce significant secondary products. Correlation of chitosanase digestibility with percentage of deacetylation provides a simple biological assay to study chitosan composition.
Biotechnology and Bioengineering - Tập 36 Số 3 - Trang 310-315 - 1990
Effects of electroconductive heat treatment and electrical pretreatment on thermal death kinetics of selected microorganisms Abstract Suspensions of yeast cell (zygo Saccharomyces bailii ) in a phosphate buffer solution were subjected to conventional (hot water) and ohmic (electric current) heating under identical temperature histories. Experiments were also conducted with cells of Escherichia coli to compare the lethal effect of combination of sublethal electrical preteatment and conventional heating with conventional heating. The kinetic parameters (D ,Z ,K and Ea ) were determined for both organisms during different treatments. There was no significant difference in the death rate of yeast cells during conventional and ohmic heating at the voltage range used in this study. Results of electrical pretreatment and conventional heating on E. coli indicated differences under certain conditions when compared with pure conventional heating. Thus it is concluded that microbial death during ohmic heating was due primarily to thermal effects with no significant effect of electric current per se. Sublethal electrical pretreatment appears to offer potential for increased bacterial inactivation in certain cases.
Biotechnology and Bioengineering - Tập 39 Số 2 - Trang 225-232 - 1992
Kinetic modeling of the enzymatic hydrolysis of pretreated cellulose Abstract The production of sugars by the enzymatic hydrolysis of cellulose is a two‐step process that includes conversion of the intermediate cellobiose to glucose by β‐glucosidase. The hydrolysis was followed by analyzing the two sugar products (cellobiose and glucose). The enzyme showed maximum activity at pH 4.8. Thermal deactivation was significant at temperatures above 45°C. At 50°C (optimum temperature) thermal deactivation was found to follow first‐order kinetics. Several models were tested by modeling the kinetics of the reaction. Their parameter values were determined by numerical optimization, including temperature dependence. The best fitting model was a competitive product inhibition for the two reactions in the operational range.
Biotechnology and Bioengineering - Tập 27 Số 9 - Trang 1282-1290 - 1985
Effects of intermittent addition of cellulase for production of <scp>L</scp>‐lactic acid from wastewater sludge by simultaneous saccharification and fermentation Abstract An attempt was made to create L ‐lactic acid, a precursor of poly‐lactic acid, which is a biodegradable plastic, from wastewater sludge from the paper‐manufacturing industry. The sludge contained a high percentage of cellulose and needed to be hydrolyzed to glucose by the action of the cellulase before being treating with lactic acid bacteria. Therefore, a method involving simultaneous saccharification and fermentation (SSF) was carried out. The optimum pH of the SSF for production of the lactic acid by the newly isolated lactic acid bacterium with a high selectively of L ‐lactic acid was found out to be around pH = 5.0, and the optimum temperature to be approximately 40°C. On the basis of the measurement of the cell density changes in the lactic acid bacteria, it was ascertained that the bacterial activity could continue at a high level for a relatively long period of time, and that the L ‐lactic acid productivity was diminished by the rapid deactivation of the cellulase. With the intermittent addition of cellulase once daily for the sake of compensating for the cellulase deactivation, the L ‐lactic acid attained a maximum concentration of 16.9 g/L, i.e., a 72.2% yield based on the potential glucose contained in the sludge under optimum pH and temperature conditions.© 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 263–270, 2003.
Biotechnology and Bioengineering - Tập 82 Số 3 - Trang 263-270 - 2003
Continuous fermentative hydrogen production from a wheat starch co‐product by mixed microflora Abstract For the transition to the hydrogen economy, hydrogen must be produced sustainably, e.g., by the fermentation of agricultural material. Continuous fermentative production of hydrogen from an insoluble substrate in nonsterile conditions is yet to be reported. In this study hydrogen production using mixed microflora from heat‐treated digested sewage sludge in nonsterile conditions from a particulate co‐product of the wheat flour industry (7.5 g L−1 total hexose) at 18‐ and 12‐hour hydraulic retention times, pH 4.5 and 5.2, 30°C and 35°C was examined. In continuous operation, hydrogen yields of approximately 1.3 moles hydrogen/mole hexose consumed were obtained, but decreased if acetate or propionate levels rose, indicating metabolism shifted towards hydrogen consumption by homoacetogenesis or propionate producers. These shifts occurred both at pH 4.5 and 5.2. Sparging the reactor with nitrogen to reduce hydrogen in the off‐gas from 50% to 7% gave stable operation with a hydrogen yield of 1.9 moles hydrogen /mole hexose consumed over an 18‐day period. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 84: 619–626, 2003.
Biotechnology and Bioengineering - Tập 84 Số 6 - Trang 619-626 - 2003
Formation and growth of heterotrophic aerobic biofilms on small suspended particles in airlift reactors Abstract In this article, the conditions for aerobic biofilm formation on suspended particles, the dynamics of biofilm formation, and the biomass production during the start‐up of a Biofilm Airlift Suspension reactor (BAS reactor) have been studied. The dynamics of biofilm formation during start up in the biofilm airlift suspension reactor follows three consecutive stages: bare carrier, microcolonies or patchy biofilms on the carrier, and biofilms completely covering the carrier. The effect of hydraulic retention time and of substrate loading rate on the formation of biofilms were investigated. To obtain in a BAS reactor a high biomass concentration and predominantly continuous biofilms, which completely surround the carrier, the hydraulic retention time must be shorter than the inverse of the maximum growth rate of the suspended bacteria. At longer hydraulic retention times, a low amount of attached biomass can be present on the carrier material as patchy biofilms. During the start‐up at short hydraulic retention times the bare carrier concentration decreases, the amount of biomass per biofilm particle remains constant, and biomass increase in the reactor is due to increasing numbers of biofilm particles. The substrate surface loading rate has effect only on the amount of biomass on the biofilm particle. A higher surface load leads to a thicker biofilm. A strong nonlinear increase of the concentration of attached biomass in time was observed. This can be explained by a decreased abrasion of the biofilm particles due to the decreasing concentration of bare carriers. The detachment rate per biofilm area during the start‐up is independent of the substrate loading rate, but depends strongly upon the bare carrier concentration. The Pirt‐maintenance concept is applicable to BAS reactors. Surplus biomass production is diminished at high biomass concentrations. The average maximal yield of biomass on substrate during the experiments presented in this article was 0.44 ± 0.08 C‐mol/C‐mol, the maintenance value 0.019 ± 0.012 C‐mol/(C‐mol h). The lowest actual biomass yield measured in this study was 0.15 C‐mol/C‐mol. © 1994 John Wiley & Sons, Inc.
Biotechnology and Bioengineering - Tập 44 Số 5 - Trang 595-608 - 1994
Scaffold‐free inkjet printing of three‐dimensional zigzag cellular tubes Abstract The capability to print three‐dimensional (3D) cellular tubes is not only a logical first step towards successful organ printing but also a critical indicator of the feasibility of the envisioned organ printing technology. A platform‐assisted 3D inkjet bioprinting system has been proposed to fabricate 3D complex constructs such as zigzag tubes. Fibroblast (3T3 cell)‐based tubes with an overhang structure have been successfully fabricated using the proposed bioprinting system. The post‐printing 3T3 cell viability of printed cellular tubes has been found above 82% (or 93% with the control effect considered) even after a 72‐h incubation period using the identified printing conditions for good droplet formation, indicating the promising application of the proposed bioprinting system. Particularly, it is proved that the tubular overhang structure can be scaffold‐free fabricated using inkjetting, and the maximum achievable height depends on the inclination angle of the overhang structure. As a proof‐of‐concept study, the resulting fabrication knowledge helps print tissue‐engineered blood vessels with complex geometry. Biotechnol. Bioeng. 2012; 109: 3152–3160. © 2012 Wiley Periodicals, Inc.
Biotechnology and Bioengineering - Tập 109 Số 12 - Trang 3152-3160 - 2012
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