Showing papers in "Biotechnology and Bioengineering in 1988"
TL;DR: This study demonstrates that shear stress in certain ranges may not be detrimental to mammalian cell metabolism, and in fact, throughout the range of shear stresses studied, metabolite production is maximized by maximizing shear Stress.
Abstract: A flow apparatus was developed for the study of the metabolic response of anchorage dependent cells to a wide range of steady and pulsatile shear stresses under well controlled conditions. Human umbilical vein endothelial cell monolayers were subjected to steady shear stresses of up to 24 dynes/sq cm, and the production of prostacyclin was determined. The onset of flow led to a burst in prostacyclin production which decayed to a long term steady state rate (SSR). The SSR of cells exposed to flow was greater than the basal release level, and increased linearly with increasing shear stress. It is demonstrated that shear stresses in certain ranges may not be detrimental to mammalian cell metabolism. In fact, throughout the range of shear stresses studied, metabolite production is maximized by maximizing shear stress.
384 citations
TL;DR: For most products of algal mass cultivation, open ponds are the only feasible photobioreactor design capable of meeting the economic and operating requirements of such systems, provided desirable species can be maintained.
Abstract: Photobioreactor design and operation are discussed in terms of mixing, carbon utilization, and the accumulation of photosynthetically produced oxygen. The open raceway pond is the primary type of reactor considered; however small diameter (1-5 cm) horizontal glass tubular reactors are compared to ponds in several respects. These are representative of the diversity in photobioreactor design: low capital cost, open systems and high capital cost, closed systems. Two 100-m(2) raceways were operated to provide input data and to validate analytical results. With a planktonic Chlorella sp., no significant difference in productivity was noted between one pond mixed at 30 cm/s and another mixed from 1 to 30 cm/s. Thus, power consumption or CO(2) outgassing limits maximal mixing velocities. Mixing power inputs measured in 100-m(2) ponds agreed fairly well with those calculated by the use of Manning's equation. A typically configured tubular reactor flowing full (1 cm diameter, 30 cm/s) consumes 10 times as much energy as a typical pond (20 cm deep flowing at 20 cm/s). Tubular reactors that flow only partially full would be limited by large hydraulic head losses to very short sections (as little as 2 m length at 30 cm/s flow) or very low flow velocities. Open ponds have greater CO(2) storage capacity than tubular reactors because of their greater culture volume per square meter (100-300 L/m(2) vs. 8-40 L/m(2) for 1-5-cm tubes). However, after recarbonation, open ponds tend to desorb CO(2) to the atmosphere. Thus ponds must be operated at higher pH and lower alkalinity than would be possible with tubular reactors if cost of carbon is a constraint. The mass transfer coefficient, K(L), for CO(2) release through the surface of a 100-m(2) pond was determined to be 0.10 m/h. Oxygen buildup would be a serious problem with any enclosed reactor, especially small-diameter tubes. At maximal rates of photosynthesis, a 1-cm tubular reactor would accumulate 8-10 mg O(2)/L/min. This may result in concentrations of oxygen reaching 100 mg/L, even with very frequent gas exchange. In an open pond, dissolved oxygen rises much more slowly as a consequence of the much greater volume per unit surface area and the outgassing of oxygen to the atmosphere. The maximum concentration of dissolved oxygen is typically 25-40 mg/L. The major advantage of enclosed reactors lies in the potential for aseptic operation, a product value which justifies the expense. For most products of algal mass cultivation, open ponds are the only feasible photobioreactor design capable of meeting the economic and operating requirements of such systems, provided desirable species can be maintained.
357 citations
TL;DR: A generalized form of Monod kinetics is proposed to account for all kinds of product, cell, and substrate inhibition, and in all cases this equation form fitted the data very well.
Abstract: A generalized form of Monod kinetics is proposed to account for all kinds of product, cell, and substrate inhibition. This model assumes that there exists a critical inhibitor concentration above which cells cannot grow, and that the constants of the Monod equation are functions of this limiting inhibitor concentration. Methods for evaluating the constants of this rate form are presented. Finally the proposed kinetic form is compared with the available data in the literature, which unfortunately is very sparse. In all cases, this equation form fitted the data very well.
341 citations
TL;DR: The bead–bead collision model is tentatively supported by the available data, but the other mechanisms may still be significant in some systems.
Abstract: The negative effects of excessive agitation on tissue cells in microcarrier culture have often been ascribed to "shear." Analysis of the fluid mechanics occurring suggests that there are actually three potential damage mechanisms: collisions of a cell-covered microcarrier with other beads, collisions with parts of the reactor (primarily the impeller), and interaction with turbulent eddies the size of the microcarrier beads. Review of the available quantitative information on agitation effects in cell cultures does not establish which mechanism is predominant; the range of experimental variables reported emphasizes power input over the other reactor and impeller parameters. The bead-bead collision model is tentatively supported by the available data, but the other mechanisms may still be significant in some systems. The formation of bead aggregates by cellular bridging provides a parallel means of damaging cells. Breaking of these bridges by any of the three means identified earlier can cause cell destruction and/or the net transfer of cells to formerly bare beads. High concentrations of bridges are favored by lower agitation rates, presumably because the bridges are not as quickly destroyed after formation.
248 citations
TL;DR: A kinetic expression was developed in which overall iron‐reduction rate is functionally related to the concentrations of both NTA and Fe(III), which indicates that reductive dissolution of hematite is driven by mineral surface area and ligand concentration.
Abstract: The kinetics and mechanism of reductive dissolution of Fe(III) oxides were examined in pure, batch cultures of Pseudomonas sp. 200. Primary factors controlling hematite dissolution kinetics were mineral surface area (or concentration of high-energy surface sites), ligand concentration, and cell number. In the presence of nitrilotriacetic acid (NTA), saturation kinetics were apparent in the relationship governing reductive dissolution of hematite. A kinetic expression was developed in which overall iron-reduction rate is functionally related to the concentrations of both NTA and Fe(III).
Addition of NTA resulted in a 20-fold increase in the microbial rate of mineral (reductive) dissolution. Mechanisms in which NTA served as a bridging ligand, shuttling respiratory electrons from the membrane-bound microbial electron transport chain to the metal center of the iron oxide, or accelerated the departure of Fe(II) centers (bound to ligand) from the oxide surface following reduction have been postulated. Experimental results indicated that cell–mineral contact was essential for reductive dissolution of goethite.
221 citations
TL;DR: It has been demonstrated that acidification is primarily determined by the hydraulic retention time and the rate of product formation by the influent substrate concentration, and the effect of the temperature followed an Arrhenius type equation with an activation energy equal to 4739 cal/mol.
Abstract: The influence of operational, parameters, such as hydraulic retention time, organic loading rate, influent substrate concentration, pH, and temperature, on the performance of the first phase of anaerobic digestion has been investigated. A complex substrate based on beef extract was used, and six series of experimental runs were conducted, each one showing the effect of one operational variable. The predominant fermentation products were always acetic and propionic acid, independent of the values of the operational parameters. For initial COD concentrations and hydraulic retention times above the critical values identified as 3 g/L and 6 h, respectively, the degree of acidification achieved was between 30 and 60%. The degree of acidification was found to increase with the hydraulic retention time and decrease with the influent substrate concentration and organic loading rate, while the opposite held true for the rate of product formation. Furthermore, it has been demonstrated that acidification is primarily determined by the hydraulic retention time and the rate of product formation by the influent substrate concentration. The concentration of the acetic acid produced was found to depend on the operational parameters. However, the concentration of propionic acid produced depended only on the substrate availability with a consistent proportion of 8% initial COD converted to it. The optimum pH and temperature were 7 and 40 degrees C, respectively. The percentage of acetic acid as a proportion of the total volatile fatty acids produced was found to increase with increasing pH and temperature, while the percentage of propionic acid seemed to decrease accordingly. Finally the effect of the temperature on the rate of acidification followed an Arrhenius type equation with an activation energy equal to 4739 cal/mol.
198 citations
TL;DR: This initial rate approach, in contrast with steady state analysis of chemostat cultures, approximates steady state behavior, since the rates were measured over brief time intervals and at low cell concentrations (< 50,000 cells/mL).
Abstract: The lack of quantitative descriptions of mammalian culture kinetics limits the ability to optimally design and control cell culture bioreactors. This limitation is ad dressed by developing mathematical equations relating the initial growth rate and the antibody productivity of the hybridoma cell line, CRL-1606, to its environmental state. This initial rate approach, in contrast with steady state analysis of chemostat cultures, approximates steady state behavior, since the rates were measured over brief time intervals and at low cell concentrations (< 50,000 cells/mL). The advantage of this approach is that it is much faster than the chemostat approach.
An equation for the growth rate was developed that superimpoed Monod equations in serum and glutamine with “noncompetitive” -type inhibition constants were inversely proportional to the lactate and ammonium concentrations. The Monod constant is critical for relating initial, low cell level culture states to other states.
Lactate was found to be the only environmental parameter that significantly inhibited antifibronectin monoclonal antibody production by the CRL-1606 hybridimas. Volumetric productivity was strictly related to culture viability, which was observed to decline at growth rates below 0.02h−1. Lactate was also found to significantly inhibit ammonium production.
183 citations
TL;DR: It appears that steam explosion increases cellulose digestibility in P. radiata by increasing fiber porosity by altering the conditions of steam explosion.
Abstract: Steam explosion after sulphur dioxide impregnation of wood chips is an effective method for improving the enzymatic digestibility of cellulose in the softwood Pinus radiata. Digestibility of pretreated fiber was progressively increased by altering the conditions of steam explosion. With increasing digestibility, there was an observed increase in fiber porosity as measured by the solute exclusion technique. Accessible pore volume and accessible surface area to a 5-nm dextran probe positively correlated with both 2- and 24-h digestion yields from pretreated fiber. The increase in accessibility was probably the result of hemicellulose extraction and lignin redistribution. A subsequent loss in accessibility, brought about by structural collapse or further lignin redistribution, resulted in a corresponding loss in digestibility. It appears that steam explosion increases cellulose digestibility in P. radiata by increasing fiber porosity.
171 citations
TL;DR: The kinetics of enzymatic hydrolysis of cellulose can be formally treated as two simultaneous pseudo‐first‐order reactions in which fast and slow hydrolyses of cellulOSE occur.
Abstract: Aspen (Populus tremuloides) and black cottonwood (Populus trichocarpa) organosolv pulps produced in a wide range of solvent composition (between 30 and 70% by volume of methanol) and catalysts (H(2)SO(4) and H(3)PO(4)) such that the cooking liquor pH
170 citations
TL;DR: Experiments are described which demonstrate that lignin removal can, indeed, be aided by treatment with xylanase from a cloned system, and that the resulting pulp retains viscosity as well as the required strength properties.
Abstract: The idea of removing lignin from kraft pulp with ligninolytic microorganisms has been around for some time.' More recently, a peroxidase has been described2 which, in the presence of low concentrations of peroxide, might depolymerize lignin and, in combination with an extraction, thereby bleach kraft pulp. An alternative approach is based on reports that residual lignin in unbleached kraft pulp is linked to hemi~ellulose~ and that cleavage of this linkage will allow lignin to be r e l e a ~ e d . ~ Hydrolysis of the lignin-hemicellulose linkage would have to be specific, in order to prevent deterioration of pulp qualities, e.g. viscosity, due to cellulose hydrolysis . 5 Ideally, the ligninhemicellulose linkage itself should be the only one cleaved. In hardwoods, the linkage is mainly betwen lignin and xylan, possibly through arabinose side chain^.^" We recently produced clones of E . coli capable of endoxylanase or P-xylosidase production in the absence of cellulase,8,' which could find potential application in lignincarbohydrate cleavage, especially for hardwood kraft pulps where xylan is the predominant hemicellulose, and can even be redeposited on the pulp during cooking." We now describe experiments which demonstrate that lignin removal can, indeed, be aided by treatment with xylanase from a cloned system, and that the resulting pulp retains viscosity as well as the required strength properties.
150 citations
TL;DR: These enzymatically prepared sugar alcohol esters have been found to be excellent surfactants in terms of their ability to reduce interfacial and surface tensions and to stabilize emulsions.
Abstract: Porcine pancreatic and Chromobacterium viscosum lipases catalyze transesterification reactions between a number of sugar alcohols and various plant and animal oils in dry pyridine. The products of this process have been identified as primary monoesters of sugar alcohols and fatty acids. These enzymatically prepared sugar alcohol esters have been found to be excellent surfactants in terms of their ability to reduce interfacial and surface tensions and to stabilize emulsions.
TL;DR: Two alternative mechanisms, inactivation of the adsorbed enzyme and mass transfer of the enzyme from the bulk solution to the solution within the cellulose fibril where the cellulase is assumed to be inactive, are used to represent the decline in activity.
Abstract: Reduction in the activity and the concentration of the adsorbed enzyme are noted in the experimental data. Two alternative mechanisms, inactivation of the adsorbed enzyme and mass transfer of the enzyme from the bulk solution to the solution within the cellulose fibril where the cellulase is assumed to be inactive, are used to represent the decline in activity. The decline in concentration of the adsorbed enzyme is represented by a modest product inhibition and, more importantly, the assumption that the concentration of the adsorption sites is proportional to the square of the remaining substrate concentration. Measurements of both adsorbed enzyme and product concentration over time are used in determining parameter values. The model is applied to a series of experiments having a 10-fold range of substrate concentration and to an experiment in which the product is removed continuously. For both deactivation mechanisms, a very good representation of product concentration (standard deviation 3.6%) is obtained over the full period (168 h) of hydrolysis; the representation of adsorbed enzyme is, however, less accurate (standard deviation 6.7-6.8%).
TL;DR: The productivity of the acetone–butanol fermentation was increased by continuously removing acetone and butanol from the fermentation broth during fed‐batch culture and the continuous extraction process provides flexible operation and lends itself to process scale‐up.
Abstract: The productivity of the acetone-butanol fermentation was increased by continuously removing acetone and butanol from the fermentation broth during fed-batch culture. Whole broth containing viable cells of Clostridium acetobutylicum was cycled to a Karr reciprocating plate extraction column in which acetone and butanol were extracted into oleyl alcohol flowing counter-currently through the column. By continuously removing these toxic metabolites from the broth, end product inhibition was reduced, and a concentrated feed solution containing 300 g/L glucose was fermented at an overall butanol productivity of 1.0 g/L h, 70% higher than the productivity of normal batch fermentation. The continuous extraction process provides flexible operation and lends itself to process scale-up.
TL;DR: An analysis of published yield data reveals that nearly complete assimilation can occur during growth on substrates with a high energy content and it will be shown that utilization of the auxiliary energy source may lead to extreme changes in the efficiency of dissimilatory processes.
Abstract: A theoretical analysis has been made of carbon conversion efficiency during heterotrophic microbial growth. The expectation was that the maximal growth yield occurs when all the substrate is assimilated and the net flow of carbon through dissimilation is zero. This, however, is not identical to a 100% carbon conversion, since assimilatory pathways lead to a net production of CO2. It can be shown that the amount of CO2 produced by way of assimilatory processes is dependent upon the nature of the carbon source, but independent of its degree of reduction and varies between 12 and 29% of the substrate carbon. An analysis of published yield data reveals that nearly complete assimilation can occur during growth on substrates with a high energy content. This holds for substrates with a heat of combustion of ca. 550 kJ/mol C, or a degree of reduction higher than 5 (e.g. ethane, ethanol, and methanol). Complete assimilation can also be achieved on substrates with a lower energy content, provided that an auxiliary energy source is present that cannot be used as a carbon source. This is evident from the cell yields reported for Candida utilis grown on glucose plus formate and for Thiobacillus versutus grown on acetate plus thiosulfate. This evaluation of the carbon conversion efficiency during assimilation also made it possible to compare the energy content of the auxiliary energy substrate added with the quantity of the carbon source it had replaced. It will be shown that utilization of the auxiliary energy source may lead to extreme changes in the efficiency of dissimilatory processes.
TL;DR: The mechanism primarily implicated in the solventogenesis process in batch fermentations of Clostridium acetobutylicum is examined in considerable detail and the action of a nonmetabolizable (FCCP) and a metabolizable (AA) uncoupler on the ΔpH, pH0, pHi, and solventogenesis were studied in order to gain further understanding ofThe solventogenesis mechanism.
Abstract: The mechanism primarily implicated in the solventogenesis process in batch fermentations of Clostridium acetobutylicum is examined in considerable detail. A variety of fermentations with or without pH control in the pH range of 3.7-6 have been carried out in order to examine which of a host of suspect parameters correlate with the initiation of solventogenesis. The parameters that did not correlate are the external (pH(0)) and intracellular (pH(i)) pH, and DeltapH, and the external or intracellular butyrate and acetate concentrations. Undissociated butyric acid (UBA) correlated well with the initiation of solventogenesis. A linear relationship between UBA and butanol concentrations was found at the onset of solventogenesis in all fermentations examined. The intercept of this linear relationship was 6-13mM UBA for the pH(0) range of 3.7-5 and approximately zero for pH(0) at or above 6. The required minimal UBA was interpreted as a dependency of the solventogenesis process on both H(+) and butyrate concentrations. Undissociated acetic acid was found not to correlate with the initiation of solventogenesis. Addition of acetoacetate (AA) and propionate enhanced the effect of UBA on the solventogenesis process. The action of a nonmetabolizable (FCCP) and a metabolizable (AA) uncoupler on the DeltapH, pH(0), pH(i), and solventogenesis were also studied in order to gain further understanding of the solventogenesis mechanism.
TL;DR: A new pilot reactor for solid‐state fermentation has been used for single‐cell protein production on raw sugar beet pulp with a mutant, Trichoderma viride T.S.S., and a material and heat balance is presented in relation with temperature and moisture level regulation during the process.
Abstract: A new pilot reactor for solid-state fermentation has been used for single-cell protein production on raw sugar beet pulp with a mutant, Trichoderma viride T.S. This pilot plant, having a maximum working capacity of one ton (ca. 200 kg dry matter) can be scaled up to the production plant level. During the process, the protein content increases from 9 to 20-21% (on the basis of dry matter) in 48 h. A material and heat balance is presented in relation with temperature and moisture level regulation during the process.
TL;DR: A dynamic model of the process was developed that describes the relation between reaction conditions and the conversion rate and it was proved that kinetic studies can be carried out with this system, operated in a batch or continuous mode.
Abstract: In the present article a method is described to immobilize lipase from Candida rugosa on a hollow fiber membrane, and the use of such a system for the hydrolysis of lipids is reported. The membranes were ENKA hydrophilic Cuprophan-type hollow fibers, having a large specific surface area. The immobilized lipase exhibited a high stability: the half-life time was 43 days at a temperature of 30 degrees C. Furthermore, it is proved that kinetic studies can be carried out with this system, operated in a batch or continuous mode. The relation between conversion rate and degree of hydrolysis was determined. On this basis, a dynamic model of the process was developed that describes the relation between reaction conditions and the conversion rate.
TL;DR: In general, serum‐free media which are “lipid rich” can sustain cell growth rates approaching that of serum supplemented cultures, however, specific antibody secretion rate is usually higher in serum‐ free media, irrespective of the lipid content.
Abstract: The replacement of serum in hybridoma cultures is considered. The focus is on the effects of serum-free media on hybridoma growth and monoclonal antibody secretion. Comparative literature data with serum supplemented cultures are discussed with an analysis of serum-free formulations and selection rules for the serum-free ingredients. In general, serum-free media which are “lipid rich” can sustain cell growth rates approaching that of serum supplemented cultures. Specific antibody secretion rate, however, is usually higher in serum-free media, irrespective of the lipid content.
TL;DR: A model is proposed that explains the insurgence of these oscillation as a consequence of changes in cell cycle parameters due to alternate growth in glucose and in ethanol as well as the complex changes of the cell population.
Abstract: Sustained oscillations have been observed in continuous cultures of Saccharomyces cerevisiae. These oscillations appear spontaneously under aerobic conditions and may constitute a severe limitation for process control. We have found that oscillations arise only in a well defined range of dilution rates and dissolved oxygen values. The period of the oscillations is related, but not equal, to the mass doubling time, and shows a relation ship with both the parent cells and daughter cells generation times. At high dilution rates two oscillatory regimens, with different periods, are observed. The analysis of the budding index shows a marked degree of synchronization of the culture, however significant differences, both in phase and in amplitude, are ob served if the budding index of parent cells and of daughter cells are considered separately. The complex changes of the cell population are clearly demonstrated by the continuous and periodic modification of both cell volume distributions and protein distributions. Ethanol is always accumulated before the drop of dissolved oxygen concentration and one of the peaks of budding index. We propose a model that explains the insurgence of these oscillation as a consequence of changes in cell cycle parameters due to alternate growth in glucose and in ethanol.
TL;DR: Over a pH range 1–4 and temperatures from 170 to 230°C, the decomposition rates of xylose, gaiactose, mannose, glucose, 2‐furfural, and 5‐hydroxymethyl‐2‐furFural (5‐HMF) were pseudo first order, and the effect of temperature and pH on the pseudo first‐order decomposition rate constants was modeled using the Arrhenius equation and acid‐base catalysis.
Abstract: Over a pH range 1-4 and temperatures from 170 to 230 degrees C, the decomposition rates of xylose, galactose, mannose, glucose, 2-furfural, and 5-hydroxymethyl-2-furfural (5-HMF) were pseudo first order. The effect of temperature and pH on the pseudo first-order decomposition rate constants was modeled using the Arrhenius equation and acid-base catalysis, respectively. Decomposition rates of the monosaccharides were minimum at a pH 2-2.5. Above pH 2.5, the monosaccharide decomposition was base catalyzed, with acid catalysis occurring at a pH of less than 2 for glucose. The furfurals were subject to acid catalysis at below ca. pH 3.5. The hydrothermal conversion of glucose to its decomposition products during thermochemical Pretreatment can be modeled as a combination of series and parallel reactions. The formation rates of identified soluble products from glucose decomposition, 5-HMF and levulinic acid, were also functions of temperature and pH. The rate of 5-HMF formation relative to glucose decomposition decreased as the pH increased from 2.0 to 4.0, with levulinic acid formation only detected when the pH was 2.5 or less. For glucose decomposition, humic solids accounted for ca. 20% of the decomposition products.
TL;DR: Experiments indicate that osmotically induced water transport (“swelling”) in the LEM system is mediated by both the carrier and the emulsion‐stabilizing surfactant, suggesting that this swell is a diffusion‐limited process.
Abstract: The separation and concentration of amino acids using liquid emulsion membranes (LEMs) are discussed. Using L- phenylalanines as a model solute, it is experimentally shown using a facilitated transport system that separation and concentration can be simultaneously achieved. The rate of separation, final product concentration, and membrane swell are shown to increase with increasing chloride driving forces in the membrane, These effects are shown to be insensitive to the particular salt used as the driving force. Changes in the carrier concentration are shown to result in higher initial fluxes and higher swell rates. Hydrodynamically induced membrane breakage is minimal for the system under consideration. Experiments indicate that osmotically induced water transport ("swelling") in the LEM system is mediated by both the carrier and the emulsion-stabilizing surfactant. The data suggest that this swell is a diffusion-limited process. The specificity of the carrier is examined and is found to be directly related to the hydrophobicity of the solute. Strategies for optimizing LEM formulations are discussed. Emphasis is placed on the hydration characteristics of the surfactant and the specificity of the carrier.
TL;DR: The hypothesis is supported by direct measurement of the pore size in two of the substrates and by diffusion inside Avicel of only smaller molecular cellulase component that when small pores dominate, the smaller enzyme components diffuse into the pores and become inactive since synergism with the larger components is no longer possible.
Abstract: The effect of cellulase size on hydrolysis was studied by comparing the behavior of crosslinked cellulase (CC) with normal cellulase (FC). The average molecular weight of the CC was at least three times the molecular weight of the FC. The amounts of each enzyme were adjusted so that the degree of solubilization after 2 h was the same. The degree of solubilization of Avicel with CC was higher than that with FC in the late stage of reaction. The degree of solubilization of pretreated lignocelluloses was much greater than that of Avicel, but the degree of solubilization with CC was lower than that with FC at all times during the reaction. The degree of solubilization of artificial lignified Avicel was higher with FC than with CC, but the degree of solubilization of de-lignified the artificial lignified Avicel was lower with FC than with CC. The degree of solubilization of amorphous celloulose with FC was the same as that with CC at all times during the reaction. These behaviors are examined by the hypothesis that when small pores dominate, the smaller enzyme components diffuse into the pores and become inactive since synergism with the larger components is no longer possible, whereas, when larger pores dominate, the entire enzyme can diffuse in and therefore the available surface area is increased. This hypothesis is supported by direct measurement of the pore size in two of the substrates and by diffusion inside Avicel of only smaller molecular cellulase component.
TL;DR: Results are presented which show how the microcarrier concentration affects the hydrodynamic environment in animal cell bioreactors and a new mechanism of hydrod dynamic damage was identified which is second order in microcarriers concentration.
Abstract: Results are presented which show how the microcarrier concentration affects the hydrodynamic environment in animal cell bioreactors. At low levels of agitation, no physical effects of microcarrier concentration were found. However, cell growth was strongly influenced by cell concentration. At high levels of agitation, a strong detrimental effect of microcarrier concentration was found. A new mechanism of hydrodynamic damage was identified which is second order in microcarrier concentration. The identification of this mechanism adds to the fundamental understanding of hydrodynamic phenomena in microcarrier bioreactors.
TL;DR: The cells appeared to regulate themselves such that energy generation is optimal subject to the constraint that the cells do not produce more reducing equivalents than can be oxidized by the electron transport system.
Abstract: Bacillus polymyxa produces (R, R)-2,3-butanediol from a variety of carbohydrates. Other metabolites are also produced including acetoin, acetate, lactate, and ethanol. The excretion of each metabolite was found to depend on the relative availability of oxygen to the culture. When the relative oxygen uptake rate was high, enhanced yields of acetate and acetoin were noted. At an intermediate oxygen availability, the butanediol yield was maximal. When the availability of oxygen was more restricted, higher yields of lactate and ethanol occurred. The cells appeared to regulate themselves such that energy generation is optimal subject to the constraint that the cells do not produce more reducing equivalents than can be oxidized by the electron transport system. The dependence of each product yield on the relative oxygen availability was determined, and this knowledge was used to carry out a fed-batch fermentation that attained a final butanediol concentration of over 40 g/L in 50 h.
TL;DR: A model was proposed which establishes a relationship between the mycelial growth and the water activity value of the substrate and optimal aw values were determined for growth and sporogenesis.
Abstract: The water activity (a(w)) of substrates has been related to the mycelial growth and the sporogenesis of two molds. In the absence of other limiting factors, optimal a(w) values were determined for growth and sporogenesis as 0.99 and 0.98, respectively, for Trichoderma viride TS and 0.97 and 0.96 for Penicillium roqueforti. In all cases, the accuracy of the optimal value would justify the regulation of this parameter. A model was proposed which establishes a relationship between the mycelial growth and the water activity value of the substrate.
TL;DR: The kinetics of anaerobic degradation of a molasses wastewater were measured under constant pH conditions in a laboratory scale packed bed reactor and, contrary to the literature and the thermo‐dynamic calculations, no inhibition was detected, biofilm diffusional effects may be the reason.
Abstract: The kinetics of anaerobic degradation of a molasses wastewater were measured under constant pH conditions in a laboratory scale packed bed reactor. In continuous and batch experiments the formation and degradation rates of the organic acids (butyric, propionic and acetic) have been followed. The influence of hydrogen gas on the acid degradation rates has been measured and, contrary to the literature and the thermo-dynamic calculations, no inhibition was detected, biofilm diffusional effects may be the reason. Two dynamic simulation models were tested, a heterogeneous model, which considered the biofilm diffusion-reaction phenomena and a quasihomogeneous model with the same kinetics. Except for hydrogen, the diffusion effects were found to be negligible. Otherwise both models gave essentially the same results and the time profiles of acids, hydrogen, carbon dioxide and methane agreed relatively well with dynamic startup experiments. Batch experiments showed the acid concentrations to be highly sensitive to the initial molasses concentration. This aspect was not included in the model but is being investigated further.
TL;DR: The results suggest that the method of formation of the cell aggregate and the details of the structure of the cells have little influence on the effective diffusive permeability, and these findings should be applicable to the transport of other small uncharged solutes, such as oxygen, that can diffuse through cells.
Abstract: Aggregates of Escherichia coli confined within hollowfiber reactors were either formed in place by culturing cells within the reactors, or were prepared by injecting a cell suspension that had been concentrated by centrifugation. The effective diffusive permeability of an uncharged nonreacting tracer, nitrous oxide, within the cell aggregates was calculated from measurements of the tracer flux through the aggregates. Estimates of the hydraulic permeability were also obtained for the aggregates that were grown in place. The effective diffusive permeability was found to decrease with increasing cell volume fraction to a value, for aggregates comprising 95% cells, of ca. 30% that obtained for cell-free buffer solution. The dependence on the cell volume fraction was described adequately by the well-known HashinShtrikman bounds for a two-phase medium. The transport properties of aggregates cultivated in place were not significantly different from those of aggregates prepared by centrifugation. Furthermore, the effective diffusive permeabilities of the tracer in aggregates prepared from cells treated with detergent or disrupted by dehydration and grinding differed only slightly from the values obtained for aggregates formed from untreated cells. The results suggest that the method of formation of the cell aggregate and the details of the structure of the cells have little influence on the effective diffusive permeability. These findings should be applicable to the transport of other small uncharged solutes, such as oxygen, that can diffuse through cells. The hydraulic permeability estimates for the aggregates cultured in place were several orders of magnitude larger than the values predicted by a theory formulated with the assumption that the cells are impervious to flow and homogeneously distributed within the aggregates. Two possible reasons for this discrepancy are, first, that there is some flow through the cells themselves, and second, that the cells may form discrete clusters separated by relatively open regions.
TL;DR: Gas holdup and oxygen transfer studies in non‐Newtonian suspensions of cellulose fibres conducted in two large reactors are described and, under identical conditions, the bubble column performed better than the airlift.
Abstract: Gas holdup and oxygen transfer studies in non-Newtonian suspensions of cellulose fibres conducted in two large (0.098 m(3) each) reactors are described. Both reactors-a bubble column and a similar internal loop airlift-were unusual in that they had rectangular cross-sections. In all cases gas holdups and k(L)a(L) declined with increasing solid concentration and, under identical conditions, the bubble column performed better than the airlift. The fluid systems used were carefully selected to represent mould fermentation broths.The behavior of true mass transfer coeffcient k(L) with changes in bubble size is discussed for these systems.
TL;DR: A laboratory model constant‐depth film fermentor was developed that enables film to be grown on any substratum and allows discrete, reproducible, and representative samples to be taken.
Abstract: A laboratory model constant-depth film fermentor was developed. Film grew on the surface of polytetrafluoroethylene (PTFE) plugs and was limited to a predetermined depth by mechanically removing excess film. Six film-forming organisms were isolated from river water and used to assess the operating characteristics of the fermentor. Film accumulation was logarithmic, and a steady state was maintained. Electron micrographs show early film development. The fermentor enables film to be grown on any substratum and allows discrete, reproducible, and representative samples to be taken.
TL;DR: In this article, a simple mathematical treatment is proposed to explain the results of the kinetics of protein degradation by alpha-amylase, and the results support evidence for an active disentanglement of chains, carried out by the different subsites of alpha-AMylase molecules.
Abstract: Native starch granules from wheat have been subjected to enzymatic depolymerization with an alpha-amylase from Bacillus subtilis. Crystallites made from short-chain amylose and residues from mild acid hydrolysis have been also tested. Electron microscopy, particle size analysis, DSC, and x-ray diffractometry reveal that enzymatic degradation occurs granule by granule. Gel permeation chromatography shows off the macromolecular nature of the remaining material. In contrast, acid erodes simultaneously all the granules, leading to a splitting into small particles. Crystalline fractions are completely degraded by alpha-amylase. These results support evidence for an active disentanglement of chains, carried out by the different subsites of alpha-amylase molecules. A simple mathematical treatment is proposed to explain the results of the kinetics.