摘要:

AbstractAn adaptive control algorithm has been implemented on a biomethanation process to maintain propionate concentration, a stable variable, at a given low value, by steering the dilution rate. It was thereby expected to ensure the stability of the process during the startup and during steady‐state running with an acceptable performance. The methane pilot reactor was operated in the completely mixed, once‐through mode and computer‐controlled during 161 days. The results yielded the real‐life validation of the adaptive control algorithm, and documented the stability and acceptable performance e

ISSN:0006-3592    

DOI:10.1002/bit.260380802

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractKinetic parameters of biological sulfide oxidation are described. The influence of the sulfide loading rate on growth yield and specific oxidation rate were investigated with free‐cell suspensions. It is concluded that at least two types of bacteria were present, namely, sulfate producers (type A) that grow at higher loading rates. Type A bacteria have a growth yield of 04 g dry S/mol S, while type B bacteria have a growth yield of 04 g dry S/mol S. Type A has a high affinity for sulfide and is inhibited by sulfide at sulfide concentrations exceeding 10 mg/L. Type B has a low affinity for sulfide and is not inhibited by sulfide, but by oxyge

ISSN:0006-3592    

DOI:10.1002/bit.260380803

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of serum on cell growth and monoclonal antibody (MAb) productivity was studied in a repeated fedbatch mode using both free‐suspended and immobilized S3H5/γ2bA2 hybridoma cells. In the suspension culture, serum influenced the cell growth rate but not the specific MAb productivity. The average specific growth rate of the suspension culture in medium containing 10% serum was approximately 0.99 ± 0.12 day−1(±standard deviation), while that in medium containing 1% serum was approximately 0.73 ± 0.12 day−1. The specific MAb productivity was almost constant at 3.69 ± 0.57 μg/106cells/day irrespective of serum concentration reached a maximum at ca. 1.8 × 106cells/mL of medium in 10% serum medium, and the cell concentration was gradually reduced to 1%. The specific MAb productivity of the immobilized cells was more than three times higher than that of the free‐suspended cells. The amount of serum in the medium did not influence the specific MAb production rate of the immobilized cells. The maintenance of high cell concentration and the enhanced specific MAb productivity of the immobilized cell culture resulted in a higher volumetric MAb productivity. In addition, MAb yield in the immobilized cell culture with medium containing 1% serum was 2.2 mg/mL of serum, which was approximately three times higher than that in the susp

ISSN:0006-3592    

DOI:10.1002/bit.260380804

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe effects of dilution rates on the performance of a two‐stage fermentation system for a recombinantEscherichia coliculture were studied. Dilution rate determines the apparent or averaged specific growth rate of a heterogeneous population of cells in the recombinant culture. The specific growht rate affects the genetic parameters involved in product formation in the second stage, such as plasmid stability, plasmid content, and specific gene expression rate. Kinetic models and correlations were developed for these parameters based on experimental data. Simulations of plasmid stability in the first stage showed that for longer fermentation periods, plasmid stability is better at higher dilution rates. However, the plasmid content is lower at these dilution rates. The optimal apparent specific growth rate for maximum productivity in the second stage was determined using two methods: (1) direct search for a constant specific growth rate, and (2) dynamic optimization using the maximum principle for a time‐dependent specific growth rate profile. The results of the calculations showed that the optimum constant apparent specific growth rate for maximum over‐all productivity is 0.40 h−1. This coincides with the optimal specific growht rate for maximum plasmid content in the expressed stage. A 3.5% increase in overall productivity can be obtained by using a linear time dependent apparent specific growth rate control, μ2(t) = 0.0007t, in the course of the fermentat

ISSN:0006-3592    

DOI:10.1002/bit.260380805

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractMorphological, geometrical, and rheological properties of the GAP A3 hybridoma cell line have been evaluated as a function of the cell cycle. Interference contrast video microscopy and scanning electron microscopy (SEM) showed that a sample of cells taken from the middle of the exponential growht phase displayed a range of cell morphologies, consistent with a heterogeneous growing culture. Micropipet manipulation was used to measure the geometrical (cell volume) and mechanical (cortical tension and apparent cell viscosity) properties of single cells selected at random from a sample in the middle of the exponential growth phase. Consistent with the range of morphologies, cell volumes (1400 to 5700 μm3) and apparent viscosities (430 to 1.2 × 104P) showed a wide range of values at 37°C, demonstrating that a hybridoma cell line cannot be characterized by a single value for any one property, and that properties must be related to their cycle dependence when considering proliferating cells. Direct, video‐microscopic observation of synchronized cells, and of individual cells that were followed throughout their cell cycle, allowed us to correlated distinct morphologies with phases of the cell cycle. As the cell cycle progresses, an increase in cell volume by a factor of 3 to 4is accompanied by an overall increase in apparent cell viscosity by approximately the same ratio, consistent with an accumulation of more cytoplasmic material in the older cells. Also, a decrease in average apparent viscosity by a factor of 10. These results are important in order to evaluate the possible role of certain structural, cell‐cycle dependent features in shear and abrasion sensitivity. This is a problem of current concern in the bioreactor culture of mammalian

ISSN:0006-3592    

DOI:10.1002/bit.260380806

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA lipase fromA spergillus niger, immobilized by adsorption on a microporous, polypropylene flat‐sheet membrane, was used to effect the continous hydrolysis of the glycerides of melted butterfat at 35°C. For the reaction conditions used in this research, a pseudo‐zero order rate expression can be used to model the kinetics of the overall hydrolysis of butterfat. Multiresponse nonlinear regression methods were employed to determine the kinetic parameters of a multisubstrate rate expression derived fro ma mechanism based on the general Michaëlis–Menten approach. For the multiresponse data taken at pH 7.0, the dependence of the maximum rate of release of each fatty acid residue of butterfat on its carbon chain length is accurately described by a skewed, bell‐shaped (or Γ‐type) distribution. Data taken at five different pH values were fit assuming a Dixon–Webb diprotic model for the pH dependence of the reaction rate. The thermal deactivation of the immobilized lipase obeyed first‐order kinetics with a half‐life of 19.9 days at 35°C. The multisubstrate model is useful for the prediction of the free fatty acid profile of lipolyzed butterfat, whereas the lumped‐substrate model provides an estimate of the overall degree of hydrolysis as a function of t

ISSN:0006-3592    

DOI:10.1002/bit.260380807

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA system comprised of an immobilized yeast reactor producing ethanol, with a membrane pervaporation module for continuously removing and concentrating the produced ethanol, was developed. The combined system consisted of two integrated circulation loops: In one the sugar‐containing medium is circulated through the membrane pervaporation module. The two loops were interconnected in a way allowing for separate parameter optimization (e.g., flow rate, temperature, pH) for each loop.The fermentation unit was 2.0 L bioreactor with five equal segments, packed with 5‐mm beads of immobilized yeasts. The bead matrix was a crosslinked polyacrylamide hydrazide gel coated with calcium alginate. The fast circulation loop of the bioreactor allowed for efficient liberation of CO2at the top of the immobilized yeast reactor. Continuous operation of the uncoupled reactor for over 50 days with inflowing defined medium or dilute molasses at a residence time of 1.25 h yielded ethanol at a rate of about 10 g/L h.The pervaporation unit was constructed from four 60‐cm‐long tubular membranes of silicone composite on a polysulfone support. The output from the fermentor was circulated through the inside of the tubes of a unit with a total surface area of 800 cm2, having an average flux of 150 mL/h, and selectivities to ethanol vs. water up to 7. A vacuum of 30 mb was applied to the outside of the tubes, removing 20–30 g of ethanol per hour, which was collected in condensors. The continuous removal of ethanol, avoiding inhibition of the fermentation process, resulted in an improved productivity and allowed the use of high sugar concentrations (40% wt/vol) offering the potential of a compact system with reduced stillage.The combined system of ethanol production and removal enabled an operative steady state at which the liquid volume of the system, and the concentrations of ethanol within the reactor (˜4% wt/vol), as well as within the flux crossing the pervaporation membrane (17%–20% wt/vol) were kept constant. At the steady state, a 40% wt/vol sugar solution could be continuously added to the fermentor when 12%–20% wt/vol clear ethanol solution was continuously removed by the pervaporation unit. Membrane fouling was reversed by short washing steps, and continuous step operation was maintained by working with two different modules that were interchanged. In this manner, long term continuous operation (over 40 days) was achieved with a productivity of 20–30 g/L h, representing over a twofold increase relative to the continuously operated reactor uncoupled from the membrane and a fivefold increase in comparison with the value obtained fro a corresponding ba

ISSN:0006-3592    

DOI:10.1002/bit.260380808

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA novel in situ microtechnique allows evaluating parameters of diffusion‐controlled reactions in biofilms. A microprobe, 15 μm in diameter, was used to simultaneously measure the dissolved oxygen concentration and the optical density at different depths in a submerged biofilm. Based on the results, the biofilm diffusion coefficient for dissolved oxygen,Dfthe dissolved oxygen flux through the biofilm surface,J02, and the half velocity coefficient,Ks, have been calculat

ISSN:0006-3592    

DOI:10.1002/bit.260380809

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA growth medium was developed for maximal production in batch culture of extracellular xylanase and β‐xylosidase byAspergillus awamoriCMI 142717 and a mutant (AANTG 43) derived from the wild‐type strain. The optimum pH for the production of xylanase and β‐xylosidase was 4.0. The best temperature of xylanase production was 30°C; 35°C was optimal for β‐xylosidase. Protease production was never completely suppressed under any of the conditions tested. However, protease titre was 3.5‐fold less than the control in medium in which proteose peptone and yeast extract were omitted: the level of xylanase was not affected (8.6 U mL−1) but β‐xylosidase titre was increased 4.7‐fold to 1.5 U mL−1. When corn steep liquor was used as the sole nitrogen source, xylanse and β‐xylosidase titres were further increased by 1.5‐ and 1.9‐fold, respectively. Of the carbon sources investigated, ball‐milled oat straw or oat spelt xylan produced the highest titres of xylanse and β‐xylosidase. None of the soluble carbon sources investigated produced the high titres of xylanase or β‐xylosidase induced by either oat straw for xylanse and β‐xylosidase was 2% and the optimum spore inoculum was between 106and 107spores/mL−1final concentration. The level of xylanse activity obtained in the culture filtrates of the mutant was a remarkable 820 U mL−1when the reducing sugar released was measured by the dinitrosalicylic acid method. This enzyme titre would appear to be the highest reported so far. The xylanases system contained the correct balance of enzymes to effect extensive hydrolysis of oat

ISSN:0006-3592    

DOI:10.1002/bit.260380810

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractAn expression system utilizing specialized ribosomes has been constructed with β‐galactosidase as the product. Ribosomes specific forlacZmRNA are generated due to a mutation within the anti‐Shine‐Dalgarno region of a plasmidborne 16S rRNA gene that is complementary to a mutation within the ribosome‐binding site oflacZ. Hence, a subpopulation of ribsomes specific for translation of the cloned gene mRNA is produced. Transcription of thelacZgene is regulated by thetacpromoter, while transcription of the mutatedrrnBlocus is controlled by the λPLpromoter. Batch experiments indicate that full induction of both operons (2 mMIPTG, 42°C) leads to maximal β‐galactosidase activity per cell at levels 35% higher than that obtained using a wild‐type ribosome expression system. Using a novel, site‐directed mutagenesis technique, construction of the specialized ribosome vector is outlined, and the results oflacZexpression are presented as transcription of both the cloned‐gene and the specialized‐ribos

ISSN:0006-3592    

DOI:10.1002/bit.260380811

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY