摘要:

AbstractRabbit articular chondrocytes were seeded onto three‐dimensional polyglycolic acid (PGA) scaffolds and placed into a closed bioreactor system. After 4 weeks of growth, meshes were examined for cartilage formation. Gross examination revealed solid, glistening material that had the appearance of cartilaginous tissue. Histologic examination revealed cell growth and deposition of extracellular matrix throughout the mesh with a less dense central core. Alcian blue and Safranin 0 staining showed deposition of glycosaminoglycans (GAGs). Immunostaining showed positive reactivity for type II collagen and chondroitin sulfate and no reactivity for type I collagen. Biochemical analysis showed collagen and GAG values to be 15% and 25% dry weight, respectively. Our results indicate that this type of system compares well with those previously described and should be useful for producing cartilage for evaluation in a clinical setting. © 1995 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260460402

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

年代:1995

数据来源: WILEY

摘要:

AbstractTissue‐engineered cartilage was cultivated under conditions of simulated microgravity using rotating bioreactors. Rotation randomized the effects of gravity on inoculated cells (chondrocytes) and permitted their attachment to three‐dimensional (3D) synthetic, biodegradable polymer scaffolds that were freely suspended within the vessel. After 1 week of cultivation, the cells regenerated a cartilaginous extracellular matrix (ECM) consisting of glycosaminoglycan (GAG) and collagen types I and II. Tissue constructs grown in simulated microgravity had higher GAG contents and thinner outer capsules than control constructs grown in turbulent spinner flasks. Two fluid dynamic regimes of simulated microgravity were identified, depending on the vessel rotation speed: (i) asettling regimein which the constructs were maintained in a state of continuous free‐fall close to a stationary point within the vessel and (ii) anorbiting regimein which the constructs orbited around the vessel spin axis. In the settling regime, the numerically calculated relative fluid‐construct velocity was comparable to the experimentally measured construct settling velocity (2–3 cm/s). A simple mathematical model was used in conjunction with measured construct physical properties to determine the hydrodynamic drag force and to estimate the hydrodynamic stress at the construct surface (1.5 dyn/cm2). Rotating bioreactors thus provide a powerful research tool for cultivating tissue‐engineered cartilage and studying 3D tissue morphogenesis under well‐defined fluid dynamic conditions. © 1995 John W

ISSN:0006-3592    

DOI:10.1002/bit.260460403

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

年代:1995

数据来源: WILEY

摘要:

AbstractGrowth of microbial and mammalian cells can be classified into substrate‐limited and substrate‐sufficient growth according to the relative availability of the substrate (carbon and energy source) and other nutrients. It has been observed for a number of microbial and mammalian cells that the consumption rate of substrate and energy (ATP) is generally higher under substratesufficient conditions than under substrate limitation. Accordingly, the product formation under substrate excess often exhibits different patterns from those under substrate limitation. The extent of increase or decrease in product formation may depend not only on the nature of limitation and cell growth rate but also on the residual substrate concentration in a relatively wide range. The product formation kinetic models existing in literature cannot describe these effects. In this study, the Luedeking–Piret kinetic is extended to include a term describing the effect of residual substrate concentration. The extended model has a similar structure to the kinetic model for substrate and energy consumption rate recently proposed by Zeng and Deckwer. The applicability of the extended model is demonstrated with three microbial cultures for the production of primary metabolites and three hybridoma cell cultures for the production of ammonia and lactic acid over a wide range of substrate concentration. The model describes the product formation in all these cultures satisfactorily. Using this model, the range of residual substrate concentration, in which the product formation is affected, can be quantitatively assessed. © 1995 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260460404

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe effect of dissolved oxygen on citric acid production and oxygen uptake byCandida lipolyticaY 1095 was evaluated in cell recycle and fed‐batch fermentation systems. The maximum observed volumetric productivity, which occurred at a dilution rate of 0.06 h−1, a dissolved oxygen concentration of 80%, and a biomass concentration of 5% w/v, in the cell recycle system, was 1.32 g citric acid/L · h. At these same conditions, the citric acid yield was 0.65 g/g and the specific citric acid productivity was 24.9 mg citric acid/g cell · h. In the cell recycle system, citric acid yields ranged from 0.45 to 0.72 g/g. Both the volumetric and specific citric acid productivities were dependent on the dilution rate and the concentration of dissolved oxygen in the fermentor. Similar productivities (1.29 g citric acid/L · h) were obtained in the fed‐batch system operated at a cycle time of 36 h, a dissolved oxygen concentration of 80%, and 60 g total biomass. Citric acid yields in the fed‐batch fermentor were consistently lower than those obtained in the cell recycle system and ranged from 0.40 to 0.59 g/g. Although citric acid yields in the fed‐batch fermentor were lower than those obtained in the cell recycle system, higher citric:isocitric acid ratios were obtained in the fed‐batch fermentor. As in the cell recycle system, both the volumetric and specific citric acid productivities in the fed‐batch fermentor were dependent on the cycle time and dissolved oxygen concentration. © 1995 Joh

ISSN:0006-3592    

DOI:10.1002/bit.260460405

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

年代:1995

数据来源: WILEY

摘要:

AbstractMicrobial degradation of trichloroethylene (TCE) has been demonstrated under aerobic conditions with propane. The primary objective of this research was to evaluate the feasibility of introducing a vapor phase form of TCE in the presence of propane to batch bioreactors containing a liquid phase suspension ofMycobacterium vaccaeJOB5 to accomplish degradation. The reactor system consisted of three phases: a vapor phase introducing air, propane, and TCE; a liquid phase of the microbial suspension; and a solid phase in the form of the microorganisms. Long‐term and initial rate experiments were conducted on three culture sets to evaluate microbial response. In two long‐term test fed propane and approximately 0.1 mg/L and 1 mg/L of TCE, respectively, propane utilization was more efficient at the high TCE concentration (600 mmol propane/mmol TCE versus 11,900 mmol propane/mmol TCE), because the propane degradation rate was approximately the same for both tests (6.73 mg/L · h and 7.85 mg/L · h for the high and low tests). In addition, TCE utilization decreased after complete propane consumption. Initial rate tests on culture sets fed propane only revealed that cells with a history of exposure to a high concentration of TCE had the highest specific growth rate, but the lowest half‐saturation constant (7.60e−3h−1and 0.10 mg/L, respectively). Tests fed variable TCE concentrations (0.031 to 5.378 mg/L in the liquid phase) with no propane showed TCE depletion but no biomass growth. The tests revealed that the TCE removal increased as the TCE concentration increased, indicating a greater removal efficiency at the higher concentrations. Tests with a constant initial propane concentration and variable liquid phase TCE concentration revealed that specific propane utilization was essentially the same. © 1995 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260460406

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe concentrations of dioctyldimethyl ammonium chloride (DODMAC) and 1‐decanol in isooctane needed to form reverse micelles by phase contact have been determined. The behavior of these reverse micelles in the extraction of aspartic acid, glutamic acid, and threonine was studied by analyzing all of the ionic species in the aqueous phase. The amino acid is extracted from the aqueous phase by exchanging with the Cl−counterions of DODMAC in the reverse micelles. The ionic species in the reverse micelles tend toward their undissociated states as the water uptake by the reverse micelles decreases. The effect of 1‐decanol on the extraction of the amino acids with two negative charges is due to the change in the water uptake of the reverse micelles. The concentration of DODMAC has no effect on the ion exchange of the amino acid with one negative charge with the Cl−counterions of DODMAC in the reverse micelles. Higher molar ratios of decanol to DODMAC favor the selective separation of amino acids with different charge numbers. © 1995 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260460407

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

年代:1995

数据来源: WILEY

摘要:

AbstractBaby hamster kidney (BHK) cell aggregates grown in stirred vessels with different working volumes and impeller sizes were characterized. Using batch cultures, the range of agitation rates studied (25–100 rpm) led to aggregates with maximum sizes of 150 μm. Necrotic centers were not observed and cell specific productivity was independent of aggregate size. High cell viability was found for both single and adherent cells without an increase in cell death when agitation rate was increased. The increase in agitation rate affected aggregates by reducing their size and increasing their concentration and cell concentration in aggregates, while increasing the fraction of free cells in suspension. The experimental relationship between aggregate size and power dissipation rate per unit of mass was close to −1/4, suggesting a correlation with a critical turbulence microscale; this was independent of vessel scale and impeller geometry over the range investigated. Viscous stresses in the viscous dissipation subrange (below Kolmogoroff eddies) appear to be responsible for aggregate breakage. Under intense agitation BHK cells grown in the absence of microcarriers existed as aggregates without cell damage, whereas cells grown on the surface of microcarriers were largely reduced. This is a clear advantage for scaleup purposes if aggregates are used as a natural immobilization system in stirred vessels. © 1995 John Wiley&Sons

ISSN:0006-3592    

DOI:10.1002/bit.260460408

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe synthesis of 3‐deoxy‐D‐arabino‐heptulosonate‐7‐phosphate (DAHP) is the first commitment of resources toward aromatics production inEscherichia coli. DAHP is produced during a condensation reaction between phosphoenolpyruvate (PEP) and erythrose 4‐phosphate (E4P) catalyzed by DAHP synthases (coded byaroF,aroG, andaroH). Stoichiometric analysis has shown a severe PEP limitation in the theoretical yield of DAHP production from glucose due to the phosphotransferase system (PTS) for sugar uptake. This limitation can be relieved by (i) the recycling of pyruvate from PEP using PEP synthase (Pps) or (ii) use of non‐PTS sugars such as xylose. Previous studies have shown the usefulness of overexpressingtktA(encoding transketolase),aroG, andpps(PEP synthase) for DAHP production in anaroBstrain unable to utilize DAHP further. In the present study we confirm the predictions of the stoichiometric analysis by introducingpps,tktA, andaroGinto vectors under independently controlled promoters. In glucose medium, although TktA has some positive effect on the final DAHP concentration, it has no effect on the yield (percent conversion). With Pps overexpression, the DAHP concentration produced from glucose is increased almost twofold and the yield is approaching the theoretical maximum, as predicted by the stoichiometric analysis. However, this Pps effect is observed only in the presence of both increased AroG and TktA. In xylose mimimal medium, the final DAHP concentration and the yield are completely determined by the AroG activity. TktA and Pps play no or insignificant roles, and the yield can reach the theoretical maximum without overexpression of these two enzymes. The results shown here are important for both rational design of metabolic pathways and industrial production of aromatics such as tryptophan, phenylalanine, indigo, quinic aci

ISSN:0006-3592    

DOI:10.1002/bit.260460409

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn the highly competitive market of commercial bakers' yeast, fermentations are operated for maximum efficiency and minimum production cost. In order to maintain competitiveness, the fermentations must be highly consistent with minimum variation in yeast performance, maximum yield on raw materials, and minimum production of undesirable side products. The use of advanced instrumentation is of critical importance to achieving these goals by the production engineer. An in situ optical density probe was used to determine the yeast cell density in full‐scale commercial bakers' yeast fermentations. The optical density probe results were compared with oxygen uptake rate analyses, packed cell volume, and off‐line measured cell dry weights. The most accurate measurement of cell density was found to be the optical density probe. This instrument allowed the on‐line determination of cell density with highly consistent results from fermentation batch to batch and with out the need for intermittent recalibration. © 1995 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260460410

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn the system composed of the cationic surfactant TOMAC (10 mM), the nonionic (co)surfactant Rewopal HV5 (2 mM), and octanol (0.1% v/v) in isooctane, reversed micelles are formed upon contact with an aqueous phase containing 50 mMethylene diamine. α‐Amylase can be transferred from the aqueous phase into reversed micelles in the pH range 9.5 to 10.5 and re‐extracted into a second aqueous phase of different composition. The size of the reversed micelles (as reflected in the water content of the organic phase) can be varied by changes in percentage of octanol, type of counterion in the aqueous phase, or in the number of ethoxylate head groups of the nonionic surfactant. An increase in size results in transfer at lower pH values. Experiments in which the charge density in the reversed micellar interface was changed by incorporation of charged derivatives of the nonionic surfactant, without influencing the water content, revealed that an increased charge density facilitated transfer, resulting in a broader transfer profile. Replacement of TOMAC by other quaternary ammonium surfactants differing in number and length of tails revealed that, of the 14 surfactants tested, only 2 gave appreciable amounts of transfer. The amount of transfer is related to the dynamics of phase separation of the surfactants: those giving a poor phase separation inactivate the enzyme. This inactivation is caused by electrostatic interactions between the charged surfactant head groups and charged groups on the enzyme. Electrostatic interactions are the first step of transfer, and can result in either incorporation in a reversed micelle, or, if reversed micelle formation is slow, in enzyme inactivation. © 1995 John Wiley&Sons

ISSN:0006-3592    

DOI:10.1002/bit.260460411

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

年代:1995

数据来源: WILEY