Biochemical Engineering Journal

Published by Elsevier
Print ISSN: 1369-703X
A gene of organic solvent-stable protease (PST-01 protease) secreted by Pseudomonas aeruginosa PST-01 was cloned and its nucleotide was sequenced. The nucleotide sequence analysis revealed that the PST-01 protease was a pseudolysin, which was an elastase produced by P. aeruginosa and was well characterized by the previous investigators. The PST-01 protease produced in recombinant Escherichia coli was not secreted into the extracellular medium, but its proenzyme was released by the lysis of the cells and became a 33.1kDa mature enzyme autoproteolytically. Its characteristics including organic solvent stability were as same as those of the PST-01 protease secreted by P. aeruginosa PST-01.
The chemical, physical and biological processes occurring in biofiltration are reviewed. A survey of operating biofilter performances is also presented and includes some novel comparative methods. It is concluded that biofiltration is a simple and cost-effective technology for odour removal and that an understanding of the many interactions occuring within the biofilter is essential for the optimal performance of the biofilter.
Three types of N-acetylated chitosans (NACs) with different degrees of acetylation (DA) were prepared and used as a substrate for enzymatic hydrolysis with a commercially available pectinase and a modified one. Pectinase modification was conducted using polyalkyleneoxide-maleic anhydride copolymer (PEO-MA copolymer). The effects of DA on enzymatic reaction with native and modified pectinases were investigated experimentally. Initial hydrolysis rate and Michaelis-Menten kinetic parameters were measured by analysis of reducing sugars. DA of NAC strongly affected the hydrolytic characteristics of native and modified pectinases. N-acetylation of chitosan increased the initial hydrolysis rate and the enzyme-substrate affinity with respect to both pectinases: NACs with DA over 0.3 showed high initial hydrolysis rate and strong affinity between enzyme and substrate. Especially, when NAC with DA over 0.3 was treated with modified pectinase, the affinity became much stronger than the native pectinase.
A new method for immobilization of alpha-amylase by UV-curing coating is proposed in this paper. The immobilization procedure of UV-curing coating on piezoelectric quartz crystal is simple and convenient, and causes less loss of enzymatic activity. The activity of the immobilized alpha-amylase is monitored by a technique based on bulk acoustic-wave (BAW) sensor. The frequency shift of BAW sensor can reflect the degree of hydrolysis of starch by the immobilized alpha-amylase. It is appropriate for the immobilized alpha-amylase to hydrolyze the soluble starch under pH 7.0 condition, which is similar to that of the free alpha-amylase. Kinetic parameters (the Michaelis constant, K(m), and the maximum initial rate V(max)) of the enzymatic hydrolysis of starch by the immobilized alpha-amylase are estimated by using a linear method of Lineweaver-Burk plot. K(m)=12.7mgml(-1) and V(max)=15.9Hzmin(-1). And the experimental results show that the immobilized alpha-amylase entrapped by the UV-curing coating retains adequate enzymatic activity and can be reused more than 50 times under certain experimental conditions.
Rigid adsorbents have advantages over soft gel media for downstream processing of proteins. The adsorption of bovine serum albumin (BSA) has been investigated on a rigid adsorbent based on a wide-pore, hydrophilically coated, silica-gel matrix. The effects of surface chemistry (weak anion exchanger and hydrophobic interaction chromatography) and particle size have been studied on the physical properties of the adsorbent and on the adsorption equilibria and adsorption kinetics. The rates of adsorption of BSA have been measured in a stirred cell and are found to be satisfactorily described by a two-step theoretical model, in which the mass transfer involves a pore diffusion resistance and an extra-particle film resistance. On the anion exchanger, the effective pore diffusivity decreases substantially with increasing protein concentration, approximately halving as the initial concentration rises from 0.7 to 2g/l. In the hydrophobic interaction chromatography medium, the pore diffusivity is less sensitive to protein concentration and is also reduced by a factor of about 4 by aggregation of the protein. Effective pore diffusivities with the "wide-pore" silica adsorbents in anion-exchange form are 36-94 times lower than the diffusivity in free solution and are comparable with the lower of the wide range of values published for soft gels.
Large scale chromatographic separation of proteins can be carried out more rapidly on rigid adsorbents than on soft gel media. The kinetics of adsorption of bovine serum albumin (BSA) have been studied on rigid adsorbents based on a wide-pore, hydrophilically-coated silica gel matrix in a packed bed (chromatographic column). Process parameters have been varied comprehensively. The effects of surface chemistry (weak anion exchanger and hydrophobic interaction), particle size and liquid flow velocity have been studied on both the adsorption and desorption processes. The relative influences of the adsorption kinetics and equilibrium isotherm on the shape of the breakthrough curve are found to vary with the process parameters in an interpretable and therefore, predictable manner. Pore diffusion resistance is dominant over the external liquid film resistance in controlling the adsorption kinetics, with Biot numbers in the range 170-2600. A two-step model based on these two resistances simulates the breakthrough curves with only limited quantitative accuracy, but gives good predictions of the effect of changes in process parameters.
Growth of heterogeneous culture collections in microtiter plates is advantageous for logistic reasons and also in enabling significant savings in medium costs, labor input and use of equipment during large screening projects. The main hurdles to overcome for aerobic microbial strains are the prevention of cross-contamination and excessive evaporation while assuring sufficient aeration rates. For this purpose we developed a sandwich spongy silicone/cotton wool cover to close the wells of square-deepwell microtiter plates. Oxygen transfer rates were derived from growth curves of Pseudomonas putida and were shown to be threefold higher during orbital shaking at a shaking diameter of 5cm at 300rpm (24mmolO(2)l(-1)h(-1) at a culture volume of 0.75ml) in comparison to a shaking diameter of 2.5cm. Photographic analysis showed a clear influence of the shaking diameter on the hydrodynamic behavior in the wells; during shaking at a 2.5cm amplitude, out-of-phase conditions occurred resulting in poor vertical mixing, while a 5cm shaking amplitude led to an optimal surface to volume ratio and a turbulent flow.
Biotin production by fermentation of recombinant Sphingomonas sp./pSP304 was investigated. A complex medium containing 60g/l of glycerol and 30g/l of yeast extract was suitable for biotin production. Biotin was produced in the late logarithmic or stationary phase after glycerol starvation. The optimum pH value for biotin production was 7.0. When the dissolved oxygen concentration (DO) was controlled at a constant level, the biotin concentration produced after 120h was significantly lower than that obtained in a test tube culture. Therefore, a batchwise jar-fermentor culture with a constant agitation speed and without DO control was conducted for investigating the effect of agitation conditions on biotin production. Six types of impeller were tested: turbine-blade type, turbo-lift type, rotating mesh type (EGSTAR((R))), screw with draft tube type, Maxblend((R))type, and anchor type. With some impellers, agitation speed was also changed. Both the maximum cell concentration and biotin production varied depending on agitation conditions. Relatively high cell concentrations were attained with four of the impeller types, turbine-blade type, rotating mesh type, Maxblend((R)) type, and anchor type. Among these impellers, the turbine-blade impeller with sintered sparger was suitable for biotin production. After 120h, the cell concentration reached an OD(660) of 43 and a biotin concentration of 66mg/l was obtained, which was comparable with the results from the test tube culture. Morphological variation was also observed depending on the agitation conditions: oval-shaped, rod-shaped, and elongated-shaped cells. Biotin production was relatively high in slightly long rod-shape cells but low in elongated cells. The difference in morphology appeared to depend on the shear stress. It was found that biotin production was strongly correlated with cell length and the oxygen transfer coefficient (k(L)a); cell lengths in the range 4-7µm and k(L)a values in the range 1.5-2.0/min were found to be suitable for biotin production in jar-fermentor culture.
Given the impact of mycelial morphology on fermentation performance, it is important to understand the factors that influence it, including agitation-induced fragmentation. The successful application of the energy dissipation/circulation function (EDC) to correlate fragmentation of Penicillium chrysogenum with agitation intensity and with different impeller types [5] has already been demonstrated. The EDC function takes into account the specific energy dissipation rate in the impeller swept volume and the frequency of mycelial circulation through that volume. In order to explore whether the EDC function can be used more generally to correlate fragmentation of different filamentous species, the present study extended the concept to agitation-induced, off-line fragmentation of Aspergillus oryzae grown in chemostat culture. The work shows that at EDC values off-line greater than that in the chemostat, fragmentation with different impellers can be correlated with the EDC. For EDC values less than those used in the chemostat, fragmentation did not occur. The earlier results of Jüsten et al. [5] with Penicillium chrysogenum are also reconsidered and found to behave similarly.
An expert system was used to achieve the high production of desulfurizing cells of Rhodococcus erythropolis KA 2-5-1. By adding a proper amount of sulfur containing component with the aid of the expert system, we could avoid excess feeding which resulted in the lowering of desulfurizing activity and starvation which caused serious damage to cell growth. In order to determine the addition amount by the expert system, the data of the amount of chemical elements contained in the cells were used as a reference for comparison with the medium components present. Culture experiments were carried out using a 5l jar fermentor with several kinds of media whose components were determined based on the inferred results with the aid of the expert system. We could restrict the amount of the sulfur component addition so that sulfur was a growth-limiting factor; in contrast, the amounts of other elements were sufficient for growth.As a result, the maximum specific production rate of 2-hydroxy biphenyl (2HBP) and the maximum cell concentration were 20mmolkg-drycells(-1)h(-1) and of 45g-drycellsl(-1), respectively. At 100h of cultivation, 1g/l of dibenzothiophene (DBT) was converted to 2HBP within 20h, i.e., 10mmolkg-drycells(-1)h(-1) of specific desulfurization activity, and the specific activity remained stable for a long period in the culture experiment.
A mathematical model is developed to describe the performance of a three-phase airlift reactor utilizing a transverse magnetic field. The model is based on the complete mixing model for the bulk of liquid phase and on the Michaelis-Menten kinetics. The model equations are solved by the explicit finite difference method from transient to steady state conditions. The results of the numerical simulation indicate that the magnetic field increases the degree of bioconversion. The mathematical model is experimentally verified in a three-phase airlift reactor with P. chrysogenum immobilized on magnetic beads. The experimental results are well described by the developed model when the reactor operates in the stabilized regime. At relatively high magnetic field intensities a certain discrepancy in the model solution was observed when the model over estimates the product concentration.
An external-loop airlift bioreactor, with a low ratio 2.9 of height-to-diameter of the riser and a ratio 6.6 of riser-to-downcomer diameter, was used to produce alpha-amylase from fermentation with dregs by Bacillus subtilis. The effects of gas flow rate and liquid volume on alpha-amylase production were investigated. After a 36-h fermentation time, an average of 432.3U/ml alpha-amylase activity was obtained under the conditions of liquid volume 8.5l and gas flow rate 1.2vvm for the first 12h of fermentation, 1.4vvm from 12 to 27h, and 1.2vvm from 27h to the end. The activity was higher than that obtained in shaking flasks (409.0U/ml) and in a mechanically stirred tank bioreactor (397.2U/ml) under optimized operating conditions. The fermentation cycle of the airlift bioreactor was shorter than the 48h required for the shaking flasks and close to the 36h of the mechanically stirred tank bioreactor. It was demonstrated that the external-loop airlift bioreactor could substitute for the traditional mechanically stirred tank bioreactor to produce alpha-amylase from fermentation by Bacillus subtilis with dregs.
An aeration strategy was proposed for foam control in an airlift reactor with double wire mesh draft tubes. The airlift reactor was employed in the cultivation of Bacillus thuringiensis for thuringiensin production. The aeration strategy involved two situations. If the foam rose and touched the foam probe, the air flow rate was dropped to a low value for a certain period. However, if the DO value was already below 10% of the saturation when the air flow rate was dropped, the conventional foam control was employed. The production of thuringiensin based on the proposed strategy was up to 70% higher than that of using the conventional cultivation method with addition of antifoam agents for foam control.
The feasibility of using shake flasks to culture animal cells was evaluated using various sizes of cylindrical shaped vessels as bioreactors. It was found that conditions can be optimized so that hybridoma, Chinese Hamster Ovary cells, and insect cells can be efficiently cultured in the shaking reactors to cell densities comparable to that obtained with stirred-jar bioreactors, and the system is scalable to larger volumes for the production of recombinant proteins or cell mass production in the laboratory.
Productivity of recombinant human alpha(1)-antitrypsin (rAAT) with a genetically engineered rice cell using an inducible promoter has been studied by batch-wise and continuous production. A simple model explained the effect of proteases released from the disrupted cells on the rAAT degradation. Glucose concentration in the medium significantly affected the rAAT productivity in the continuous production, because the rAAT was induced by sugar depletion. When the fresh medium containing 5mM glucose was supplied to the continuous bioreactor, induction time was long and the productivity was low, indicating that the glucose concentration in the cells was high enough as to repress the promoter. When the glucose concentration in the fresh medium was reduced to 0.5mM, total amount of rAAT produced in 70h cultivation reached 6.7-7.6mg/g-dry cell, which was two times larger than the control medium without glucose.
Extractive aqueous two-phase fermentation of endoglucanase, a key enzyme for the conversion of cellulosic substances to fermentable sugars, from an intergeneric fusant of Trichoderma reesei/Saccharomyces cerevisiae is a meaningful approach for better production and simple recovery of this enzyme. A phase composition of 6.5% (w/w) dextran and 7.5% (w/w) polyethylene glycol 6000, having a partition coefficient of 2.89 and 1.31 for endoglucanase from an intergeneric fusant of T. reesei/S. cerevisiae and T. reesei (WT) (being a control in this study), respectively, was chosen for extractive fermentation of the enzyme. Endoglucanase production is higher in medium containing polyethylene glycol (PEG) 6000 than in medium without PEG 6000. Comparative analysis of endoglucanase fermentation by fusant and T. reesei was carried out in shake culture and environment-controlled bioreactor conditions. The fusant produced 0.43U of endoglucanase (overall production: 0.34U) in the top phase of an aqueous two-phase system (ATPS), compared to 0.3U in medium without the phase system in shake culture. In a batch reactor, the endoglucanase level for the fusant in the top phase of ATPS was 0.49U (overall production: 0.40U), compared to 0.38U produced in medium without aqueous two-phase components. To corroborate this study, T. reesei produced 8.41U of endoglucanase (overall production: 5.96U) in the top phase of ATPS, compared to 7.18U in the medium without the phase system in shake culture. On the other hand, in a batch bioreactor, T. reesei produced 10.13U of endoglucanase (overall production: 6.90U) in the top phase of ATPS, compared to 8.56U of the enzyme in medium without aqueous two-phase components. The lower overall enzyme production by T. reesei in the two-phase system might be due to limitation in oxygen transfer to the dispersed phase where the enzyme is produced. A higher cell concentration and a reduced lag phase was obtained in ATPS, compared to a similar medium without phase forming polymers for both the intergeneric fusant of T. reesei/S. cerevisiae and T. reesei.
The biotransformation of beta-ionone by Aspergillus niger IFO 8541 entrapped in Ca-alginate beads was investigated in a two-phase liquid system, due to the low aqueous solubility of the precursor. Modelling of phase transfer processes of the substrate demonstrated that the solute was transferred from the organic droplets to the gas, giving a loss by stripping, and then from the gas to the aqueous solution where a chemical degradation occurred. The biological reaction took place after direct precursor transfer from the organic layer to the biocatalyst by surface adsorption. Studies on the biological process demonstrated the critical effect of the biomass content in the medium at the time at which beta-ionone was added. Optimum conditions involved fed-batch feedings of both precursor and carbon source (sucrose) after the biomass concentration reached a value close to 6.8g/l. The biotransformation process then took place at a constant rate of 0.046mmol/lh with a reaction yield, defined with respect to beta-ionone metabolised by the fungus, close to unity. Best results achieved in this study allowed to obtain 3.5g/l biological compounds after 400h reaction.
The use of embryonic stem cells (ESCs) and their progeny in high throughput drug discovery and regenerative medicine will require production at scale of well characterized cells at an appropriate level of purity. The adoption of automated bioprocessing techniques offers the possibility to overcome the lack of consistency and high failure rates seen with current manual protocols. To build the case for increased use of automation this work addresses the key question: "can an automated system match the quality of a highly skilled and experienced person working manually?" To answer this we first describe an integrated automation platform designed for the 'hands-free' culture and differentiation of ESCs in microwell formats. Next we outline a framework for the systematic investigation and optimization of key bioprocess variables for the rapid establishment of validatable Standard Operating Procedures (SOPs). Finally the experimental comparison between manual and automated bioprocessing is exemplified by expansion of the murine Oct-4-GiP ESC line over eight sequential passages with their subsequent directed differentiation into neural precursors. Our results show that ESCs can be effectively maintained and differentiated in a highly reproducible manner by the automated system described. Statistical analysis of the results for cell growth over single and multiple passages shows up to a 3-fold improvement in the consistency of cell growth kinetics with automated passaging. The quality of the cells produced was evaluated using a panel of biological markers including cell growth rate and viability, nutrient and metabolite profiles, changes in gene expression and immunocytochemistry. Automated processing of the ESCs had no measurable negative effect on either their pluripotency or their ability to differentiate into the three embryonic germ layers. Equally important is that over a 6-month period of culture without antibiotics in the medium, we have not had any cases of culture contamination. This study thus confirms the benefits of adopting automated bioprocess routes to produce cells for therapy and for use in basic discovery research.
Chlorella pyrenoidosa was cultivated under photoautotrophic, mixotrophic and cyclic light-autotrophic/dark-heterotrophic conditions. The influence of light on the carbon and energy metabolism of microalgae was investigated by the use of metabolic flux analysis. The respiratory activity of microalgae in the light was assessed from the autotrophic flux distribution. Results showed that the glycolytic pathway, tricarboxylic acid cycle and mitochondrial oxidative phosphorylation maintained high activities during illumination, indicating little effect of light on these pathways, while the flux through the pentose phosphate pathway during illumination was very small due to the light-mediated regulation. The theoretical yields of biomass on ATP decreased in the following order: heterotrophic culture>mixotrophic culture>autotrophic culture, and a significant amount of the available ATP was required for maintenance processes in microalgal cells. The energy conversion efficiency between the supplied energy to culture, the absorbed energy by cells and the free energy conserved in ATP were analyzed for the different cultures. Analysis showed that the heterotrophic culture generated more ATP from the supplied energy than the autotrophic and mixotrophic cultures. The maximum thermodynamic efficiency of ATP production from the absorbed energy, which was calculated from the metabolic fluxes at zero growth rate, was the highest in the heterotrophic culture and as low as 16% in the autotrophic culture. By evaluating the energy economy through the energy utilization efficiency, it was found that the biomass yield on the supplied energy was the lowest in the autotrophic cultivation, and the cyclic culture gave the most efficient utilization of energy for biomass production.
This paper describes the enzymatic hydrolysis of solid residue of olive mill (OMRS) in a batch reactor with the Trichoderma reesei enzyme. Before enzymatic saccharification, crude lignocellulosic material is submitted to alkaline pre-treatment with NaOH. Optimum conditions of the pre-treatment (temperature of T=100 degrees C and OMRS-NaOH concentration ratio of about R=20) were determined. The optimum enzymatic conditions determined were as follows: pH of about 5, temperature of T=50 degrees C and enzyme to mass substrate mass ratio E/S=0.1g enzyme (g OMRS)(-1). The maximum saccharification yield obtained at optimum experimental conditions was about 50%. The experimental results agree with Lineweaver Burk's formula for low substrate concentrations. At substrate concentrations greater than 40gdm(-3), inhibitory effects were encountered. The kinetic constants obtained for the batch reactor were K(m)=0.1gdm(-3)min(-1) and V(m)=800gdm(-3).
The probability of complete loss of plasmid material from plasmid bearing cells undergoing active growth has been modelled and incorporated into predictions for the dynamic concentrations of plasmid bearing cells in both batch and continuous flow, stirred tank bioreactors. The new model is based on an extension of the well-used model of Imanaka and Aiba [Ann. New York Acad. Sci. 369 (1981) 1] and is relatively easy to use compared to complex structured models. The new model predicts that both accelerating and decelerating rates of plasmid loss occur in both batch and continuous flow operation, and agrees well with data collected here and published earlier by others.
In the culture of red beet hairy roots in shaking flasks, a period for acclimation without lateral root generation existed at the early stage, and the root tip meristems containing growing points (GPs) were found to be damaged under an elevated shear stress condition. The loading experiments of shear stress to the hairy roots revealed that the GPs subjected to the acclimation acquired tolerance to shear stress, retaining relatively high viability of GPs up to 0.6N/m(2) of loaded shear stress. Next, the hairy roots after culture for 50h at 0.05N/m(2) of shear stress were exposed to conditions at various levels of shear stress in a single column reactor, and a relatively high growth rate was obtained in the vicinity of 1.0N/m(2) of shear stress. According to these results, two-stage cultures of hairy roots were then performed, which was comprised of a first stage for 50h at 0.05N/m(2) of shear stress for the prevention of decay of the GPs caused by hydraulic stress and a second stage for 110h at 1.0N/m(2) of shear stress for active elongation of the GPs with sufficient nutrient supply by regulation of the medium flow rate. The cell concentration ultimately reached 7.6kg dry cells/m(3), although no growth was observed in the case where the hairy roots did not undergo the first stage.
As part of a research program aimed at producing biodiesel fuel from plant oils enzymatically cells of Rhizopus oryzae (R. oryzae) IFO4697 (with a 1,3-positional specificity lipase) immobilized within biomass support particles (BSPs) were investigated for the methanolysis of soybean oil. The R. oryzae cells easily became immobilized within the BSPs during batch operation. To enhance the methanolysis activity of the immobilized cells under the culture conditions used, various substrate-related compounds were added to the culture medium. Among the compounds tested, olive oil or oleic acid was significantly effective. In contrast, no glucose was necessary. Immobilized cells were treated with several organic solvents, but none gave higher activity than untreated cells. When methanolysis was carried out with stepwise additions of methanol using BSP-immobilized cells, in the presence of 15% water the methyl esters (MEs) content in the reaction mixture reached 90% - the same level as that using the extracellular lipase. The process presented here, using a whole cell biocatalyst, is considered to be promising for biodiesel fuel production in industrial applications.
The capacity of the microbes to reduce the metal has been demonstrated. The immobilised induced microbes with toxic chemical CuCl(2) was used to reduce the Cu ions as elemental metal and by using the response surface methodology the parameters such as the inducer concentration, the time of inducer addition which are concerned with the growth and formation of specific enzymes and the initial substrate concentration, initial pH of the substrate solution and the time of reaction which are concerned with the biocatalytic reduction of the metal ions were optimised for maximum reduction. The elemental copper reduced and removed experimentally from its ionic state at the optimum conditions was 54.82ppm.
This paper combines Sturm's method with the tangent analysis method to solve a biochemical reaction involving multiplicity. This method can easily derive the necessary conditions for multiplicity. In addition, we find a starting bifurcation point for multiplicity which cannot be obtained by the tangent method alone. Moreover, a start-up strategy is suggested to obtain a high conversion and unique steady state in four selected kinetic models of biochemical reactions, with inhibition.
Glucosamine measurement has been tested as the indirect method to estimate the biomass produced by Cunninghamella elegans during solid state cultivation (SSC). The independence of this cell constituent content from the age and the conditions of the culture have been verified. The influence of the medium composition, in particular the nature of the carbon source on glucosamine amount is presented. Glucosamine can be considered as a well-adapted biomass indicator, with the necessity to establish for each medium tested a prior correlation between biomass and glucosamine amount. This correlation should be defined in submerged conditions before applying the biomass estimating method in SSC.
The characteristics of polyvinyl alcohol (PVA) and calcium alginate as immobilization matrices were examined and compared for the uptake of gold by a fungal biomass. PVA-immobilized biomass showed superior mechanical strength and chemical stability. In addition, PVA beads were also stable under a wider range of pH (1-13). The lower mass transfer resistance in PVA beads was evident from kinetic studies which showed a significantly shorter period of time for the immobilized PVA beads to achieve 80% gold removal as compared with immobilized alginate beads. Calculated rate constants and maximum rates for the uptake of gold by both immobilized PVA and immobilized alginate biosorbent revealed a much more rapid uptake phenomenon by the former. BET analyses also indicated a larger surface area and larger pore size distribution in PVA beads, further indicating a lower resistance to mass transfer. Gold biosorption in the immobilized PVA bead could be modeled by both the Langmuir and Freundlich adsorption isotherms.
The economy of scaling-up a bioreactor by increasing the number of units was investigated with respect to an integrated flowsheet. For the production of t-PA from animal cells, a base case flowsheet using a single large bioreactor was compared to a multiple bioreactor case. Simulation of the complete flowsheets for the two cases showed that a multiple bioreactor approach to scale-up increases the return of investment (ROI) of the base process by 122%. This enormous increase in ROI results from the smaller size of the downstream units compared to the base case, since downstream processing accounts for about 80% of the total cost for high value products like t-PA. Proper scheduling of the downstream units allowed sharing of the equipment by the bioreactors. A breakdown of the equipment purchase cost showed that cost related to cell culture equipment increased from 14% for the base case to about 37% for the multiple bioreactor case. The contribution from chromatography columns to the total equipment purchase cost, on the other hand, decreased from 52 to 33%.
The gas-liquid mass transfer coefficient K(L)a in the fermenter is a strong function of mode of energy dissipation and physico-chemical properties of the liquid media. A combination of disc turbine (DT) and pitched blade turbine down flow (PTD) impellers has been tested in laboratory bioreactor for gas hold-up and gas-liquid mass transfer performance for the growth and biotransformation medium for an yeast isolate VS1 capable of biotransforming benzaldehyde to L-phenyl acetyl carbinol (L-PAC) and compared with those in water.Correlations have been developed for the prediction of the fractional gas hold-up and gas-liquid mass transfer coefficient for the above media. The mass transfer coefficient and respiration rate have been determined in the shake flask for the growth as well as for biotransformation medium. These results, then have been used to optimize the operating parameters (impeller speed and aeration) for growth and biotransformation in a laboratory bioreactor. The comparison of cell mass production and L-PAC production in the bioreactor has been done with that obtained in shake flask studies.
An agitated 12-well microtiter plate system with a working volume of 2ml was investigated for cell culture process development. Agitation assures homogeneity in wells and enhances mass transfer between the gas and the liquid phase, thus improving maximum cell density and pH stability. The pH of the NaHCO(3)-buffered system can be adjusted by altering the carbon dioxide content of the gas phase. The non-toxic, visual pH indicator phenol red was used in combination with a spectrophotometric plate reader for rapid and precise pH measurements. For high throughputs, cell growth was assessed non-invasively using stable green fluorescent protein (GFP) expressing cells and a fluorescence plate reader. The setup is simple and inexpensive. The system can be automated and allows several hundred small-scale bioreactor experiments to be run in parallel.
The light distribution in the externally illuminated cylindrical photo-bioreactor for production of hydrogen by a photosynthetic bacterium Rhodobacter capsulatus ST-410 was estimated. The estimation was performed on the basis of the Matsuura and Smith's diffuse model [1]. In the diffuse model, the incident light rays are assumed to proceed in every direction and the local intensity is calculated as the sum of the intensities of light. Since Lambert-Beer's law, extensively used in photometry, was not useful for explaining the decrease in the intensity of light by the biomass, an empirical expression was used. The measurement of the intensities from every direction was conducted in an externally illuminated cylindrical photo-bioreactor having an inner diameter of 60mm and a working volume of 550ml. The obtained results confirmed our estimation. The light distribution was applied to estimate the hydrogen production by R. capsulatus ST-410 using the same photo-bioreactor. The overall hydrogen-production rate was successfully estimated.
One of the important parameters in characterising fermentations of aerobic microorganisms is the specific power consumption. A new method has been introduced which enables the accurate determination of the power consumption in shaking bioreactors. It is based on torque measurements in the drive and the appropriate compensation of the friction losses. Measurements of the power consumption revealed the phenomenon of the liquid being 'out-of-phase' for the first time for shaking bioreactors. This occurs at certain operating conditions and is characterised by an increasing amount of liquid not following the rotating movement of the shaker table, thus reducing the specific power consumption, mixing and the gas/liquid mass transfer. With respect to this, different hydrodynamic cases have to be distinguished. All these cases have in common, however, that the probability of 'out-of-phase' conditions increases with lower shaking diameters, lower filling volumes, larger number and sizes of baffles and higher viscosity. For unbaffled flasks with a nominal volume </=1l the 'out-of-phase' phenomenon is described in the form of a newly defined non-dimensional Phase number (Ph). To avoid the (unidentified) development of a screening project in unfavourable directions or even its complete failure, researchers must be aware of the 'out-of-phase' phenomenon. The experimental protocols have to be carefully selected so that the occurrence of such unwanted hydrodynamic conditions is not possible under all experimental circumstances.
The maximum gas-liquid mass transfer capacity of 250ml shaking flasks on orbital shaking machines has been experimentally investigated using the sulphite oxidation method under variation of the shaking frequency, shaking diameter, filling volume and viscosity of the medium. The distribution of the liquid within the flask has been modelled by the intersection between the rotational hyperboloid of the liquid and the inner wall of the shaking flask. This model allows for the calculation of the specific exchange area (a), the mass transfer coefficient (k(L)) and the maximum oxygen transfer capacity (OTR(max)) for given operating conditions and requires no fitting parameters. The model agrees well with the experimental results. It was furthermore shown that the liquid film on the flask wall contributes significantly to the specific mass transfer area (a) and to the oxygen transfer rate (OTR).
The overall diffusion coefficients for several low molecular weight solutes, such as glucose, fructose, sucrose, lactose, and vitamin B(12) have been determined in Ca-alginate membrane liquid-core capsules using the unsteady-state method following the release of solutes from the capsules to a well-stirred solution of limited volume. The diffusion coefficients obtained for saccharides were 5-20% lower than the corresponding diffusivity in water while for vitamin B(12) about 50% that of water. The diffusion coefficients of the investigated capsules were not influenced by the change in alginate concentration in the capsule membrane from 0.5 to 1.0%. Lower diffusivities and higher deviations from the diffusivity in water were obtained for higher molecular weight solutes.
Positional enrichment analysis has become an important technique for assessing detailed flux distributions and the fates of specific atoms in metabolic pathway systems. The typical approach to positional enrichment analysis is performed by supplying specifically labeled substrate to a cell system, letting the system reach steady state, and measuring where label had arrived and accumulated. The data are then evaluated mathematically with the help of a linear stoichiometric flux distribution model. While this procedure has proven to yield new and valuable insights, it does not address the transient dynamics between providing label and its ultimate steady-state distribution, which is often of great interest to the experimentalist (pulse labeling experiments). We show here that an extension of a recent mathematical method for dynamic labeling analysis is able to shed light on these transitions, thereby revealing insights not obtained with traditional positional enrichment analyses. The method traces the dynamics of one or more carbons through fully regulated metabolic pathways, which, in principle, may be arbitrarily complex. After a brief review of the earlier method and description of the theoretical extension, we illustrate the method with an analysis of the pentose phosphate pathway in Zymomonas mobilis, which has been used for traditional positional enrichment analyses in the past. We show how different labeling schemes result in distinctly different transients, which nevertheless eventually lead to a steady-state labeling profile that coincides exactly with the corresponding profile from traditional analysis. Thus, over the domain of commonality, the proposed method leads to results equivalent to those from state-of-the-art existing methods. However, these steady-state results constitute only a small portion of the insights obtainable with the proposed method. Our method can also be used as an "inverse" technique for elucidating the topology and regulation of pathway systems, if appropriate time series data are available. While such dynamic data are still rather rare, they are now being generated with increasing frequency and we believe it is desirable, and indeed necessary, to accompany this trend with an adequate, rigorous method of analysis.
A surfactant-lactoperoxidase (LPO) complex catalytically active in organic solvents was developed by the emulsion coating method. The oxidation of 2,6-dimethoxyphenol (2,6-DMP) was conducted by the surfactant-LPO complex in organic media. The LPO complex efficiently catalyzed the oxidation of 2,6-DMP in various organic solvents, although lyophilized LPO did not display the catalytic activity at all. To optimize the preparation and reaction conditions for the surfactant-LPO complex, we examined the effects of pH value in the water pools of W/O emulsions, kinds of oxidants, and the nature of organic solvents on the oxidation reaction. Its optimum activity was obtained when the pH value of the aqueous enzyme solution was adjusted to ca. 8 at the preparation stage. The LPO complex exhibited the highest catalytic activity in chloroform when H(2)O(2) was employed as the oxidant. Furthermore, the storage stability of the surfactant-LPO complex was far better than that of the surfactant-horseradish peroxidase complex. This high storage stability of the LPO complex will be a benefit for industrial usage of peroxidases.
Glucoamylase, as a model enzyme, was immobilized on a ceramic membrane modified by surface corona discharge induced plasma chemical process-chemical vapor deposition (SPCP-CVD). Characterizations of the immobilized enzyme were then discussed. Three kinds of ceramic membranes with different amounts of amino groups on the surface were prepared utilizing the SPCP-CVD method. Each with 1-time, 3-times and 5-times surface modification treatments and used for supports in glucoamylase immobilization. The amount of immobilized glucoamylase increased with the increase in the number of surface modification treatments and saturated to a certain maximum value estimated by a two-dimensional random packing. The operational stability of the immobilized glucoamylase also increased with the increase in the number of the surface treatment. It was almost the same as the conventional method, while the activity of immobilized enzyme was higher. The results indicated the possibility of designing the performance of the immobilized enzyme by controlling the amount of amino groups. The above results showed that the completely new surface modification method using SPCP was effective in modifying ceramic membranes for enzyme immobilization.
In order to characterize the contributions of respiratory and photosynthetic actions to energy conversions, the mixotrophic cells of Marchantia polymorpha were cultivated in the medium containing 10kg/m(3) glucose as an organic carbon source. The cultures were conducted with the supply of ordinary air (0.03% CO(2)) at constant incident light intensities of 50 and 180W/m(2). From the results of metabolic analysis, it was found that the cell yield based on ATP synthesis was estimated to be 6.3x10(-3)kg-dry cells/mol-ATP in these cultures. Under the examined conditions, energy conversion efficiency through respiration was larger than that through photosynthesis, and efficiency of overall energy conversion to ATP was maximized when the sum of energies from glucose and light captured by the cells was approximately 7.2x10(5)J/(hkg-dry cells). Taking into account the efficiency of overall energy conversion, a batch culture of M. polymorpha in a bioreactor was carried out by regulating incident light intensity ranging from 9 to 58W/m(2). In the culture with light regulation, the cell yield of 6.2x10(-9)kg-dry cells/J was achieved on the basis of energy provided to the system throughout the culture, and this value was 2.3 and 9.3 times as large as those obtained in the cultures under constant incident light intensities of 50 and 180W/m(2), respectively.
Kinetic resolution of racemic compounds by enzymatic hydrolysis with non-enantioselective separation of enantiomer products via a separator or ion-pair formation has been quantitatively analyzed. Theoretical results indicate that the removal of chiral products has profound effects on improving the conversion and enantiomeric excess for the desired chiral substrate or product. The analysis was confirmed from lipase-catalyzed hydrolysis of racemic methyl 2-chloropropionate in the presence of pyrrolidine in buffer saturated dichloromethane.
An esterification process was developed for the direct synthesis of 2-hydroxy-5-hexenyl 2-chlorobutyrate ester from 2-chlorobutyric acid by using the epoxide 1,2-epoxy-5-hexene and Mucor miehei immobilised lipase as the biocatalyst in a batch reactor. The effect of temperature, catalyst concentration, and substrate and product concentration has been studied. An ordered Bi Uni enzymatic mechanism with competitive inhibition by the epoxide and acid has been proposed. The corresponding kinetic parameters were calculated by non-linear regression. Activation energy shows a value of 8.04kcal/mol. The thermodynamic parameters of the process, enthalpy and entropy, were 15.4kcal/mol and 45cal/mol, respectively.
Cholesterol, a major component of plasma membrane lipid rafts, is important for assembly and budding of enveloped viruses, including influenza and HIV-1. Cholesterol depletion impairs virus assembly and infectivity. This study examined the effects of exogenous cholesterol addition (delivered as a complex with methyl beta cyclodextrin) on the production of Molony murine leukemia virus retroviral vector and HIV-1-based lentiviral vector pseudotyped with the vesicular stomatitis virus glycoprotein (VSV-G). Cholesterol supplementation before and during vector production enhanced the infectivity of retroviral and lentiviral vectors up to 4-fold and 6-fold, respectively. In contrast, the amount of retroviral vector produced was unchanged, and that of lentiviral vector was increased less than two-fold. Both free cholesterol and cholesterol ester content in 293-gag-pol producer cells increased with cholesterol addition. In contrast, the phospholipids headgroup composition was essentially unchanged by cholesterol supplementation in 293-gag-pol packaging cells. Based on these results, it is proposed that cholesterol supplementation increases the infectivity of VSV-G-pseudotyped retroviral and lentiviral vectors, possibly by altering the composition of the producer cell membrane where the viral vectors are assembled and bud, and/or by changing the lipid composition of the viral vectors.
A novel miniaturized system has been developed for measuring protein-protein interactions in solution with high efficiency and speed, and minimal use of protein. A chromatographic monolith synthesized in a capillary is used in the method to make interaction measurements by self-interaction chromatography (SIC) in a manner that, compared to column methods, is more efficient as well as more readily practicable even if only small amounts of protein are available. The microfluidic monolith requires much less protein for both column synthesis and the chromatographic measurements than a conventional SIC system, and in addition offers improved mass transfer and hence higher chromatographic efficiency than for previous SIC miniaturization systems. Protein self-interactions for catalase as a model protein, quantified by measurement of second virial coefficients, B(22), were determined by SIC and follow trends that are consistent with previously reported values. Different column derivatization conditions were studied in order to optimize the chromatographic behavior of the microfluidic system for SIC measurements. Chromatographic sensitivity can be further increased by using different column synthesis conditions.
High quality, intact messenger RNA (mRNA) is required for DNA microarray and reverse transcriptase polymerase chain reaction analysis and is generally obtained from total RNA isolations. The most widely recognized measure of RNA integrity is the RNA Integrity Number (RIN) obtained from the Agilent Bioanalyzer, as it provides sizing, quantification, and quality control measures. This work describes comparisons of the RIN values obtained for recombinant E. coli. Uninduced recombinant E. coli cultures were examined, as well as induced cultures that produced either a soluble or insoluble recombinant protein. The uninduced cultures and the induced cultures producing soluble protein had higher RIN values than the induced cultures producing insoluble protein. These lower RIN values for E. coli producing the insoluble protein indicate that cellular degradation of the ribosomal RNA species is the likely cause of the lower RIN values. As the use of DNA microarrays and other gene expression tools increase in usage in the industrial recombinant protein production community, these results suggest the need for further studies to determine acceptable RIN ranges for gene expression analysis and effects of various culture conditions on RIN values for recombinant E. coli.
Recombinant bacterial cells in a fermentation broth rarely contain the same number of plasmids, even though this simplification is often used. Recent work has however indicated limitations of the simplified approach. Based on these studies, the distribution of plasmid copy numbers per cell has been represented macroscopically here in a Gaussian form for the fraction of biomass as a function of the copy number. Applying this distribution and an experimentally validated kinetic model to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) synthesis by Escherichia coli containing the plasmid pBR Eco gap, it is seen that GAPDH production in a batch fermentation is maximized by a particular initial (non-zero) copy number variance and an optimal duration. To implement this distribution in a bioreactor, it is suggested that the profile may be discretized, inocula corresponding to the mean copy number of each fraction prepared, and then combined to obtain the seed culture.
The effects of different organic solvents (paraffin, organic acid, alcohol and ester) and their volumetric fractions on the cell growth and Taxol production were studied in two-liquid-phase and the two-stage culture. A kinetic model, incorporated the effects of the toxicity of organic solvents was developed for two-liquid-phase culture of Taxus cuspidata in the two-stage Taxol production. The results showed that the proposed kinetic model could fit the experimental data satisfactorily. The results also showed that Taxol production could reach the optimal value when 10-logP was in the range of 2 to 5 and the volumetric fraction of the organic solvents at the corresponding the highest Taxol production should be lower when 10-logP was high.
The use of human pluripotent stem cells, including embryonic and induced pluripotent stem cells, in therapeutic applications will require the development of robust, scalable culture technologies for undifferentiated cells. Advances made in large-scale cultures of other mammalian cells will facilitate expansion of undifferentiated human embryonic stem cells (hESCs), but challenges specific to hESCs will also have to be addressed, including development of defined, humanized culture media and substrates, monitoring spontaneous differentiation and heterogeneity in the cultures, and maintaining karyotypic integrity in the cells. This review will describe our current understanding of environmental factors that regulate hESC self-renewal and efforts to provide these cues in various scalable bioreactor culture systems.
The transport of paclitaxel in Taxus canadensis suspension cultures was studied with a fluorescence analogue of paclitaxel (Flutax-2(®)) in combination with flow cytometry detection. Experiments were carried out using both isolated protoplasts and aggregated suspension cell cultures. Flutax-2(®) was shown to be greater than 90% stable in Taxus suspension cultures over the required incubation time (24 hours). Unlabeled paclitaxel was shown to inhibit the cellular uptake of Flutax-2(®), although structurally similar taxanes such as cephalomannine, baccatin III, and 10-deacetylbaccatin III did not inhibit Flutax-2(®) uptake. Saturation kinetics of Flutax-2(®) uptake was demonstrated. These results indicate the presence of a specific transport system for paclitaxel. Suspension cells elicited with methyl jasmonate accumulated 60% more Flutax-2(®) than unelicited cells, possibly due to an increased cellular storage capacity following methyl jasmonate elicitation. The presence of a specific mechanism for paclitaxel transport is an important first result that will provide the basis of more detailed studies as well as the development of targeted strategies for increased paclitaxel secretion to the extracellular medium.
A one-dimensional age-based population balance model of the cell cycle is proposed for a mouse-mouse hybridoma cell line (mm321) producing immunoglobulin G antibody to paraquat. It includes the four conventional cell cycle phases, however, G1 is divided into two parts (G1a and G1b). Two additional phases have been added, a non-cycling state G1', and a pre-death phase D. The duration of these additional phases is determined by cumulative glutamine content and ammonia concentration, respectively. It is assumed that glutamine is only consumed during G1 and antibody is only produced during G1b and S, the kinetics are assumed to be zero-order. Glucose is consumed throughout the cell cycle at a rate that is dependent upon its prevalent concentration. Ammonia and lactate are produced in direct proportion to glutamine and glucose consumption, respectively. Parameters in the model have been determined from experimental data or from fitting the model to post-synchronisation data. The model thus fitted has been used to successfully predict this cell lines behaviour in conventional batch culture at different initial glutamine concentrations, and in chemostat culture at steady-state and in response to a glutamine pulse. The model predicts viable cell, glutamine, glucose and lactate kinetics well, but there are some discrepancies in the prediction for ammonia and antibody. Overall, the results obtained support the assumptions made in the model relating to the regulation of cell cycle progression. It is concluded that this approach has the potential to be exploited with other cell lines and used in a model-based control scheme.
A modified method for determination of diffusivities of low molecular substances in non-Newtonian liquids described by the power-law model has been proposed. It is based on the dissolution of Geiss body, with a parameter m=1/3 rotating in an infinite fluid. In this case, the solution of the differential equations of motion and mass transfer is available as an analytical formula for calculating the diffusivity coefficient.The method allows the extension of the variety of media and diffusing species. It has been illustrated with dissolving of gypsum in water and five non-Newtonian liquids. The results obtained have been interpreted taking into account the interaction between calcium ions and polymer molecules of the non-Newtonian system, as well as the heterogeneity of the system near to the dissolving surface.
Top-cited authors
Ashok Pandey
  • Indian Institute of Toxicology Research
Jochen Büchs
  • RWTH Aachen University
Jo-Shu Chang
  • National Cheng Kung University
Carlos Soccol
  • Universidade Federal do Paraná
Aniruddha Bhalchandra Pandit
  • Institute of Chemical Technology, Mumbai