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Showing papers in "Biotechnology and Bioengineering in 1985"


Journal ArticleDOI
TL;DR: The rate of the hydrolysis of cellulose was so low that this was shown to be the rate‐limiting step in overall anaerobic digestion and elucidated the true rate‐ Limiting step of an aerobic digestion.
Abstract: The characteristics of the degradation of cellulose, soluble starch, and glucose in the acidogenic phase and the effects of the substrate loading rate and biological solids retention time on the methanogenic phase of anaerobic digestion were investigated. The results obtained from continuous experiments using laboratory-scale anaerobic chemostat reactors elucidated the true rate-limiting step of anaerobic digestion. The specific rate of substrate utilization decreased in the following order: glucose, soluble starch, acetic acid, and cellulose. The rate of the hydrolysis of cellulose was so low that this was shown to be the rate-limiting step in overall anaerobic digestion. Among methanogenic bacteria Methanosarcina would provide a higher substrate utilization rate than Methanothrix, and the maximum allowable substrate loading rate in the methanogenic phase was 11.2 g acetic acid/L day.

364 citations


Journal ArticleDOI
TL;DR: The microencapsulation procedure, by protecting transplanted tissue from the components of the immune system, has great clinical potential as a new form of treatment for diseases such as diabetes and liver disease.
Abstract: An improved membrane has been developed for the microencapsulation of islets of Langerhans which protects these cells from the immune system. These requirements were accomplished through the optimization of important microencapsulation parameters and through the improved biocompatibility of a new alginate-poly-l-lysine (PLL)-alginate capsule membrane. Spherical and smooth microcapsules could be formed by utilizing a purer sodium alginate and by keeping the viscosity of the sodium alginate solution above 30 cps. The strength of the capsule membrane was enhanced by increasing the alginate-PLL reaction time as well as the PLL concentration. The permeability of the membrane [4 mum thick, 93% (w/w) water] was a function of the viscosity average molecular weight (Mv) of the PLL (Mv = 4000-4 x 10(5)) used in the encapsulation procedure. Microcapsules prepared with PLL with Mv = 1.7 x 10(4) were the least permeable, being impermeable to normal serum immunoglobulin, albumin, and haemoglobin. The microencapsulation procedure, by protecting transplanted tissue from the components of the immune system, has great clinical potential as a new form of treatment for diseases such as diabetes and liver disease.

359 citations


Journal ArticleDOI
TL;DR: The inhibitory effect of ethanol on yeast growth and fermentation has been studied for the strain Saccharomyces cerevisiae ATCC No. 4126 under anaerobic batch conditions and two kinetic models appear to accurately represent the experimental data.
Abstract: The inhibitory effect of ethanol on yeast growth and fermentation has been studied for the strain Saccharomyces cerevisiae ATCC No. 4126 under anaerobic batch conditions. The results obtained reveal that there is no striking difference between the response of growth and ethanol fermentation. Two kinetic models are also proposed to describe the kinetic pattern of ethanol inhibition on the specific rates of growth and ethanol fermentation: microi/micro0 = 1 - (P/Pm)alpha (for growth) nui/nu0 = 1 - (P/P'm)beta (for ethanol production). The maximum allowable ethanol concentration above which cells do not grow was predicted to be 112 g/L. The ethanol-producing capability of the cells was completely inhibited at 115 g/L ethanol. The proposed models appear to accurately represent the experimental data obtained in this study and the literature data.

280 citations


Journal ArticleDOI
TL;DR: During the course of the delignification reaction, O2 is evolved from the reaction mixture indicating active H2O2 decomposition, and the total amount of O2 evolved is inversely proportional to the amount of substrate present, indicating that some of the peroxide oxygen becomes incorporated into lignin degradation products.
Abstract: Alkaline solutions of hydrogen peroxide partially delignify wheat straw and other lignocellulosic materials, leaving a cellulosic residue that is highly susceptible to enzymatic digestion by cellulase. The delignification reaction is strongly dependent upon the pH of the reaction mixture, with an optimum at pH 11.5-11.6, pKa for the dissociation H(2)O(2) right harpoon over left harpoon H(+) + HOO(-). The data are consistent with a mechanism in which H(2)O(2) decomposition products such as .OH and O(2) (-)., rather than H(2)O(2) or HOO(-), are the primary lignin oxidizing species. During the course of the delignification reaction, O(2) is evolved from the reaction mixture indicating active H(2)O(2) decomposition. At a given concentration of H(2)O(2), the rate of O(2) evolution is proportional to the amount of lignocellulosic substrate present in the reaction mixture. However, the total amount of O(2) evolved is inversely proportional to the amount of substrate present, indicating that some of the peroxide oxygen becomes incorporated into lignin degradation products. The amount of peroxide oxygen incorporated can range as high as 2 O(2) per lignin C(9) unit, depending upon the initial concentration of lignocellulosic substrate.

263 citations


Journal ArticleDOI
TL;DR: The microbial epoxidation of propene and 1‐butene was used to study some fundamental aspects of two‐liquid‐phase biocatalytic conversions and high activity retention was favored by a low polarity in combination with a high molecular weight.
Abstract: The microbial epoxidation of propene and 1-butene was used to study some fundamental aspects of two-liquid-phase biocatalytic conversions. Introduction of a water-immiscible organic solvent phase in a free-cell suspension gave rise to a series of undesired phenomena, e.g., inactivation by the solvent, clotting of biomass, and aggregation of cells at the liquid-liquid interface. Immobilization of the cells in hydrophilic gels, e.g., calcium alginate, prevented direct cell-organic solvent contact and the related clotting and aggregation of biomass. However, the gel entrapment did not seem to provide additional protection against the organic solvent. The influence of various organic solvents on the retention of immobilized-cell activity was related to solvent properties like the polarity (as expressed by the Hildebrand solubility parameter) and the molecular size (as expressed by the molecular weight or molar volume). High activity retention was favored by a low polarity in combination with a high molecular weight. The solubility parameter also proved useful to describe the capacity of various organic solvents for oxygen and alkene oxides. This facilitated the optimization of the solvent polarity.

248 citations


Journal ArticleDOI
TL;DR: The overall efficiency of plasmid gene expression, measured as the ratio of β‐lactamase specific activity toplasmid content, decreased significantly with increasing plasmids content in LB medium.
Abstract: Plasmid–host cell interactions have been investigated experimentally using Escherichia coli HB101, plasmid RSF1050 which contains the origin of replication of pMB1, and four other closely related copy number mutant plasmids. Growth characteristics of these recombinant strains and β-lactamase activity expressed from a plasmid gene were investigated in Luria broth (LB) and in minimal medium (M9) containing in some cases casamino acids or different concentrations of α-methylglucoside, a competitive inhibitor of glucose transport. Maximum specific growth rates in LB and minimal media were reduced for increasing plasmid content per cell. Plasmid copy number increased when specific growth rate was reduced by changing medium composition. Growth rates of high copy number strains were less sensitive to α-methylglucoside than lower copy number strains and the plasmidfree host. The overall efficiency of plasmid gene expression, measured as the ratio of β-lactamase specific activity to plasmid content, decreased significantly with increasing plasmid content in LB medium.

241 citations


Journal ArticleDOI
TL;DR: The two major types of airlift contactors, concentric‐tube and external‐loop, were investigated for their gas holdup (riser and downcomer) and overall mass transfer characteristics.
Abstract: The two major types of airlift contactors, concentric-tube and external-loop, were investigated for their gas holdup (riser and downcomer) and overall mass transfer characteristics. Results obtained in batch charges of tap water and 0.15 kmol/m(3) NaCl solution are reported for external-loop airlift contactors having downcomer-to-riser cross-sectional area ratios, A(d)/A(r), ranging from 0.11

192 citations


Journal ArticleDOI
TL;DR: Hydrolysis of xylan‐associated acetyl groups was found to occur at the same rate as that ofxylan, except at 100°C, where acetyl is released preferentially, and no effect of acid concentration on the rate of acetyl removal relative to that of x Dylan was evident.
Abstract: Batch hydrolysis kinetics of paper birch (Betula papyrifera) xylan and its associated acetyl groups in dilute sulfuric acid have been measured for acid concentrations of between 0.04 and 0.18M and temperatures of between 100 and 170°C. Only 5% of the cellulose was hydrolyzed for up to 85% xylan removal. Rate data were correlated well by a parallel reaction model based on the existence of reactive and resistant xylan portions. The resulting rate equation predicts the experimental xylan concentrations in the residue to within 10%. Hydrolysis of xylan-associated acetyl groups was found to occur at the same rate as that of xylan, except at 100°C, where acetyl is released preferentially. No effect of acid concentration on the rate of acetyl removal relative to that of xylan was evident.

192 citations


Journal ArticleDOI
TL;DR: The growth of the hydrocarbon‐rich alga Botryococcus braunii was studied under “air‐lift” conditions using batch and continuous cultures and the main features of phosphate nutrition in B.braunii and its effects on hydrocarbons were examined.
Abstract: The growth of the hydrocarbon-rich alga Botryococcus braunii was studied under “air-lift” conditions using batch and continuous cultures. Large variations in the physiological state of B. braunii were achieved in batch cultures and in continuous cultures with various dilution rates. The possible effects of these variations upon hydrocarbons (nature, relative abundance, location, level, productivity) and also on the production of exocellular polysaccharides were examined. The relationships between the physiological state of B. braunii and its hydrocarbon and polysaccharide production were discussed and compared with those generally observed in unicellular algae. The factors giving rise to the transition from high to low productivity stages were considered. To this end we examined, at first, the variations in cell ultrastructure and the resulting degeneration occurring during batch cultures. Afterward the parallel changes in some parameters of the medium (pH, phosphate level) were determined and their possible relationships with B. braunii growth and hydrocarbon production were discussed. The main features of phosphate nutrition in B. braunii and its effects on hydrocarbons were finally examined.

188 citations


Journal ArticleDOI
TL;DR: The use of a two‐stage continuous culture system coupled with a temperature sensitive expression system allows a high trpA productivity from the derepressed plasmid for more than 48 h and also offers a possibility of minimizing the instability problem of high expression recombinants.
Abstract: Derepression of the phage lambda p(L) promoter on recombinant plasmid pPLc 23-trpAl caused a rapid increase of plasmid free segregants in the population. In continuous culture, increased production of trpA protein follwing derepression was accompanied by a continuous deceleration of specific growth rate. In the repressed condition, plasmid loss per generation in continuous culture decreased as dilution rate increased from 0.06 to 1.08 h(-1). Over this range, the concentration of plasmid DNA within the cell decreased eightfold corresponding to a decrease in plasmid number from 74 to 32 molecules/cell. The use of a two-stage continuous culture system coupled with a temperature sensitive expression system allows a high trpA productivity from the derepressed plasmid for more than 48 h and also offers a possibility of minimizing the instability problem of high expression recombinants. Such a system also permits the critical study of the effects of fermentation and other regulatory parameters on expression under better controlled conditions than is possible in a batch culture or single-stage continous culture.

183 citations


Journal ArticleDOI
TL;DR: Human embryonic kidney cells grown as an attached, confluent monolayer on a flat substrate were subjected to steady, uniform laminar flow of medium in a specially designed chamber in which flow patterns and shear stress are accurately defined and controlled.
Abstract: Human embryonic kidney cells grown as an attached, confluent monolayer on a flat substrate were subjected to steady, uniform laminar flow of medium in a specially designed chamber in which flow patterns and shear stress are accurately defined and controlled. Experiments were performed for shear stress levels ranging from 0.2 to 6.0 N/m(2) with times of exposure to the shear stress ranging from 2 to 24 h. The influence of the shear field was slight at low shear stress (0.26 N/m(2)). Higher stress levels (0.65 N/m(2) and higher) had significant effects on cell morphology, and on the post-shear release of urokinase enzyme. Still higher stress levels (2.6 N/m(2) and higher) caused marked reduction in cell viability. These results may be of interest in addressing practical problems in developing commercial biosynthesis reactors.

Journal ArticleDOI
TL;DR: The experiments seem to confirm the hypothesis that solvent production is controlled by the demand and availability of ATP, and that the pH affects the availability of organic nitrogen.
Abstract: In batch fermentations of C. acetobutylicum, with 5 g/L yeast extract and 50mM glucose, the ratio of ammonium to glucose affected solvent production when the pH was left to vary uncontrolled from 4.5 to 3.65. High solvent production was observed for a low ratio. When the pH was controlled at 4.5, only acids were produced for all ratio values. At a low ammonium-to-glucose ratio, solvents were produced when the pH was controlled at 3.7. Acids only were produced for a low ratio value at pH 4.0 or for a high ratio value at pH 3.7. In continuous cultures, mostly acids were produced under glucose limitation, but solvents were produced under nitrogen limitation. It was concluded that the nitrogen availability controls solvent production and that the pH affects the availability of organic nitrogen. Biomass autolysis at the stationary phase of batch cultures was reversibly inhibited at pH values less than 3.8. In batch fermentations, the overall molar growth yields on ATP (Y(ATP)) varied from 5.5 to 9.0 and the transient yields from 5.5 to 15.5. In continuous cultures, the Y(ATP) values varied from 5.5 to 14.7 under glucose limitation, and from 6.1 to 9.3 under nitrogen limitation. The Y(ATP) depended on the ammonium to glucose ratio and the culture pH, but did not show the usual dependence on the specific growth rate in batch cultures. The experiments seem to confirm the hypothesis that solvent production is controlled by the demand and availability of ATP.

Journal ArticleDOI
TL;DR: A solubilization model was developed which was used to predictBiodegradability of whole samples based on solids and filtrate biodegradabilities and the effect of NaOH on the solubILization of cell wall constituents and potential problems of toxicity are discussed.
Abstract: Wheat straw was treated with NaOH and anaerobically digested for methane production. Alkaline treatment resulted in a greater than 100% increase in biodegradability of wheat straw. The potential of a process flow scheme employing high alkali concentration at ambient temperature with solids separation and recycle of filtrate containing residual alkali was explored. The effect of NaOH on the solubilization of cell wall constituents and potential problems of toxicity are discussed. A solubilization model was developed which is used to predict biodegradability of whole samples based on solids and filtrate biodegradabilities. Energy requirements and chemical costs are also addressed.

Journal ArticleDOI
TL;DR: Comment les cellules initient la biodegradation, mecanisme d'attaque des composes xenobiotiques, devenir des produits provenant du metabolisme and du cometabolisme, besoins associes a l'emploi de systemes avec substrats melanges.
Abstract: Article de synthese sur la base microbiologique de la biodegradation de composes organiques: comment les cellules initient la biodegradation, mecanisme d'attaque des composes xenobiotiques, devenir des produits provenant du metabolisme et du cometabolisme, besoins associes a l'emploi de systemes avec substrats melanges, importance et interaction dans les communautes microbiennes, evolution de nouvelles voies (genie genetique et plasmide). Tests de biodegradabilite aerobies et anaerobies

Journal ArticleDOI
TL;DR: High‐level yeast inocula was investigated as a means of overcoming the toxicity problem in ethanol fermentation of acid hydrolyzate of wood cellulose, and continuous fermentation with cell recycle was superior to batch fermentation in that there was no overall cell decline and the ethanol yield was substantially higher.
Abstract: High-level yeast inocula was investigated as a means of overcoming the toxicity problem in ethanol fermentation of acid hydrolyzate of wood cellulose. When the inoculum level exceeded 10(8) initial cells/mL, 50% of the yeast cells survived the initial cell death period during which furfural and HMF were depleted. The fermentation thus proceeded to completion by virtue of cell regrowth. The specific ethanol productivity in batch fermentation on the basis of viable cells was comparable to that of pure glucose fermentation. Continuous fermentation with cell recycle was superior to batch fermentation in that there was no overall cell decline and the ethanol yield was substantially higher. The maximum ethanol productivity in continuous fermentation was 4.9 g/L h and it occurred at a dilution rate of 0.24 hr(-1).

Journal ArticleDOI
TL;DR: A new technique is presented for the production of immobilized biocatalyst/presupport mixture in uniform droplets by means of a resonance technique, which is small and comparable to that found in the corresponding conventional procedures.
Abstract: A new technique is presented for the production of immobilized biocatalysts in large quantities. It consists of breaking up a jet of the biocatalyst/presupport mixture in uniform droplets by means of a resonance technique. Entrapment of yeast and plant cells in calcium alginate has been used as the model. The production capacity of the nozzles used (0.5, 0.8, and 1.1 mm exit diameters) is two orders of magnitude larger than the production capacity of the conventional techniques (maximum capacity with a 1.1-mm nozzle diameter is 24 L/h). Depending on frequency, nozzle diameter, and volumetric flow rate, the bead size varies between 1 and 2 mm, with standard deviations of 3-5% for yeast immobilization and 10-15% for plant cells. The deactivation of both yeast and plant cells is small and comparable to that found in the corresponding conventional procedures.

Journal ArticleDOI
TL;DR: The thermophilic UASB process was investigated, with Glucose chosen as the substrate because granulation is reported to occur in UASb reactors when it is the substrate for a acid-formation process.
Abstract: In recent years numerous designs have been developed for the high-rate anaerobic treatment of wastewater.'-6 All these processes have their advantages and drawbacks, which have been discussed repeatedly (see, for example, ref. 7). Of these processes, the upflow anaerobic sludge blanket (UASB) process is currently the most widely applied, at least in Western Europe. It is successfully applied in the treatment of wastewaters from maize and potato starch industries and sugar beet and potato processing industries.' Perhaps the main advantage of the UASB process is that no specific support material is required. However, this main advantage may sometimes be a serious drawback: the absence of support material necessitates the availability of a sludge with very good settling properties. Whenever such a sludge is obtained, or can be maintained, successful operation of the UASB process is readily achieved. Under certain circumstances the settleability of the sludge in UASB reactors is greatly improved because bacterial growth is in the form of spherical flocs with a quite consistent structure, normally referred to as granular sludge.6 Although already considerable research has been performed on factors considered to be important in the phenomenon of gran~lation,~-" the knowledge on this matter is still relatively poor. Thermophilic anaerobic digestion may become an attractive alternative for mesophilic digestion because of the higher growth rates of the bacteria involved and, consequently, the higher maximum activities per unit of biomass. As the specific growth rates of the methane-forming bacteria of the genus Methanothrix, which are believed to be the predominant acetoclastic methanogens in methane digestion processes with a high biomass retention time,L2313 is ca. 2.5 times as high at 55°C as at 30°C,'2.'3 also a 2.5 times higher methanogenic acitivity per unit of biomass may be expected. Also, in thermophilic sewage sludge digestion a Methanosarcina was found to be the predominant acetoclastic methanogen, which even has a higher specific growth rate than the thermophilic Methanothrix. l 4 The successful operation of high-rate thermophilic systems requires a high activity per unit of volume, and therefore a high biomass retention is a prerequisite. In view of the successful use under mesophilic conditions, we investigated the thermophilic UASB process for this purpose. Glucose was chosen as the substrate because granulation is reported to occur in UASB reactors when it is the substrate for a acid-formation process."

Journal ArticleDOI
TL;DR: Fermentation (stoichiometric) equations are derived for anaerobic saccharolytic fermentations of butanediol and mixed acids and it is shown that the equations are useful for checking the consistency of experimental data, for calculating maximal yields and selectivities for the fermentation products, and calculating the extent of utilization of the Embden–Meyerhof–Parnas pathway versus the Hexose Monophosphate pathway of glucose utilization.
Abstract: Using the available information of fermentation biochemistry, fermentation (stoichiometric) equations are derived for anaerobic saccharolytic fermentations of butanediol and mixed acids. The equations describe the interrelations among the fermentation products, biomass, and consumed substrate (glucose). The validity of the equations is tested using a variety of batch data from the literature. The validity of the equations is expected to extend to steady-state and transient fermentations, as well. Uses, improvements, and extensions of the equations are also discussed in detail. Among others, it is shown that the equations are useful for checking the consistency of experimental data, for calculating maximal yields and selectivities for the fermentation products, and calculating the extent of utilization of the Embden-Meyerhof-Parnas pathway versus the Hexose Monophosphate pathway of glucose utilization. 37 references.

Journal ArticleDOI
TL;DR: The results show that agitation and pressure are important parameters for solvent productivity in acetone‐butanol fermentation.
Abstract: Batch fermentations were run at varying agitation rates and were either pressurized to 1 bar (15.2 psig) or nonpressurized. Agitation and pressure both affect the level of dissolved hydrogen gas in the media, which in turn influences solvent production. In nonpressurized fermentations volumetric productivity of butanol increased as the agitation rate decreased. While agitation had no significant effect on butanol productivity under pressurized conditions, overall butanol productivity was increased over that obtained in the nonpressurized runs. Maximum butyric acid productivity, however, was found to occur earlier and increased as agitation increased. Peak hydrogen productivity occurred simultaneously with peak butyric acid productivity. The proporation of reducing equivalents used in forming the above products was determined using a redox balance based on the fermentation stoichiometry. An inverse relationship between the final concentrations of acetone and acetoin was found in all fermentations studied. The results show that agitation and pressure are important parameters for solvent productivity in acetone-butanol fermentation.

Journal ArticleDOI
TL;DR: A critical cell number model was proposed to elucidate the mechanism of the inoculum requirement and used to simulate cell distribution and growth on microcarriers under different cultivation conditions and identified a critical number of cells per microcarrier.
Abstract: For the cultivation of mammalian cells on microcarriers a minimum inoculum concentration is required to initiate cell attachment and subsequent cell growth. A critical cell number model has been proposed to elucidate the mechanism of the inoculum requirement. In this model it was hypothesized that after inoculation a critical number of cells per microcarrier is required for normal growth to occur; failure to acquire enough cells will impede cell growth. This critical cell number model was expressed mathematically and used to simulate cell distribution and growth on microcarriers under different cultivation conditions. By comparing the simulated growth kinetics with the experimental results, the actual critical cell number per microcarrier was identified. The critical number could be reduced by employing an improved medium for the cultivation.

Journal ArticleDOI
TL;DR: A cybernetic framework is presented which views microbial response in multiple substrate environments as a judicious investment of cellular resources in synthesizing different key proteins according to an optimal regulatory strategy.
Abstract: A cybernetic framework is presented which views microbial response in multiple substrate environments as a judicious investment of cellular resources in synthesizing different key proteins according to an optimal regulatory strategy. A mathematical model is developed within the cybernetic framework for the diauxic growth of Klebsiella pneumoniae on a mixture of D-glucose and D-xylose. The "bang-bang" optimal policy describes well the experimental observations obtained using a fermenter coupled to an Apple II microcomputer. Striking variations in respiratory levels are observed experimentally during the switching of the cell's adaptive machinery for the utilization of the less preferred substrate.

Journal ArticleDOI
TL;DR: A new hybrid reactor, the upflow blanket filter (UBF), which combined on open volume for a sludge blanket and submerged plastic rings (Flexiring, Koch Inc., 235 m2/m3) in the upper one‐third of the reactor volume, was studied and was found to be very efficient in retaining biomass.
Abstract: A new hybrid reactor, the upflow blanket filter (UBF), which combines an open volume in the bottom two-thirds of the reactor for a sludge blanket and submerged plastic rings (Flexiring, Koch Inc., 235 squared m/cubic m) in the upper one-third of the reactor volume, was studied. This UBF reactor was operated at 27 degrees C at loading rates varying from 5 to 51 g chemical oxygen demand (COD)/l day with soluble sugar wastewater (2500 mg COD/l). Maximum removal rates of 34 g COD/l day and CH/sub 4/ production rates of 7 vol/vol day (standard temperature and pressure (STP)) were obtained. The biomass activity was about 1.2 g COD/g volatile suspended solids per day. Conversion (based on effluent soluble COD) was over 93% with loading rates up to 26 g COD/l day. At higher loading rates conversion decreased rapidly. The packing was very efficient in retaining biomass. 11 references.

Journal ArticleDOI
TL;DR: The equations for anaerobic fermentations of propionic‐acid bacteria and for production of various oxychemicals from pentoses, hexoses, and cellobiose are shown to be valuable for calculating maximal yields and selectivities of the various fermentation products and as “gateway sensors” for monitoring of the fermentations.
Abstract: Fermentation (stoichiometric) equations are derived for anaerobic fermentations of propionic-acid bacteria (of both the Propionibacterium and acrylate pathways) and for production of various oxychemicals (butanol, acetone, isopropanol, butanediol, butyrate, acetate, propionate, succinate, lactate, and acrylate) from pentoses, hexoses, and cellobiose. The derivations of the equations are based on the fermentation biochemistries of the various bacterial classes. The validity of the equations is tested using fermentation data from the literature. The equations are shown to be valuable, among other uses, for calculating maximal yields and selectivities of the various fermentation products, as "gateway sensors" for monitoring of the fermentations, and for calculating the extents of the various intracellular reactions of the fermentation biochemistry.

Journal ArticleDOI
TL;DR: Cell biomass grown on solid substrate was estimated by measuring oxygen consumption rate and glucosamine content of the cells and this reliable method of estimating the cell growth rate enabled us to simulate the enzyme production in a solid culture system by means of multiple linear regression analysis.
Abstract: Production of cellulase using solid culture systems of Trichoderma reesei QM9414 and Sporotrichum cellulophilum on wheat bran was studied. By using moisture-controlled solid culture equipment, the effect of water content of wheat bran on cell growth and cellulase production was investigated. Cellular biomass grown on solid substrate was estimated by measuring oxygen consumption rate and glucosamine content of the cells. These parameters were shown to have a good linear correlation with the specific growth rate. This reliable method of estimating the cell growth rate enabled us to simulate the enzyme production in a solid culture system by means of multiple linear regression analysis which takes into account of the water content, cell mass, and the oxygen consumption rate as variables. The cell growth and cellulase production were maximized at different water content of the medium. A high water content, 57% for T. reesei and 70% for S. cellulophilum, favored mycelial growth, while the maximum cellulase activity was obtained at a lower water content such as 50% for both fungi. It was observed that cellulase production by T. reesei depended on the culture conditions that support the optimal growth rate for the maximum enzyme production.

Journal ArticleDOI
TL;DR: The model agrees well with two existing experimental studies of anaerobic digestion of biomass particulates and Hypothetical computer simulations are presented to illustrate possible instabilities of theAnaerobic process under various operating scenarios.
Abstract: Anaerobic digestion of biological organic particulates to methane has been described by a structured mathematical model based on multiple-reaction stoichiometry, conventional material balances, and liquid phase equilibrium chemistry. A general stoichiometric treatment for any set of multiple biological reactions is derived based on a unit mass of oxggen equivalents of the reactions limiting substrate. The model agrees well with two existing experimental studies of anaerobic digestion of biomass particulates. Hypothetical computer simulations are presented to illustrate possible instabilities of the anaerobic process under various operating scenarios.

Journal ArticleDOI
TL;DR: The effect of feast/famine growth conditions on activated sludge cultures indicates that nonfilamentous cultures can be selected by providing proper substrate gradients and extended periods of endogenous metablism, suggesting a selection advantage to microbes capable of readily assimilating substrate materials and maintaining viability during extended starvation periods.
Abstract: The effect of feast/famine growth conditions on activated sludge cultures indicates that nonfilamentous cultures can be selected by providing proper substrate gradients and extended periods of endogenous metablism. Reactor operating strategies providing intermittently high substrate concentrations result in cultures characterized by high peak substrate and oxygen uptake activities, rapid settling rates, and high resistance to starvation. Sludge settleability can be manipulated using controlled variations in growth environment with corresponding changes noted in sludge activity. In combination with the low net growth rates associated with activated sludge systems, feast/famine environments would logically convey a selection advantage to microbes capable of readily assimilating substrate materials and maintaining viability during extended starvation periods.

Journal ArticleDOI
TL;DR: The extension from static column cultivation to stirred tank reactor of 65 L capacity gave similar yields of cellulase and the effects of fermentation conditions, such as moisture content, pH, temperature, and aeration, on cellulase production by Trichoderma harzianum using a mixture of wheat straw and bran were investigated.
Abstract: Cellulase production from lignocellulosic materials was studied in solid-state cultivation by both static and mixed techniques under nonaseptic conditions. The effects of fermentation conditions, such as moisture content, pH, temperature, and aeration, on cellulase production by Trichoderma harzianum using a mixture of wheat straw (80%) and bran (20%) were investigated. With a moisture content of 74% and a pH of 5.8., 18 IU filter paper activity and 198 IU endoglucanase activity/g initial substrate content were obtained in 66 h. The extension from static column cultivation to stirred tank reactor of 65 L capacity gave similar yields of cellulase.

Journal ArticleDOI
TL;DR: The bistaged pH process for the production of pullulan enhanced the polysaccharide concentration in the medium, influenced the rheological properties of the fermentation broth, and has a potential of operation under nonsterile and nonaseptic conditions.
Abstract: Two strains of the yeast-like fungus Aureobasidium pullulans 2552 and 140B have been used for the fermentative production of the polysaccharide pullulan from a sucrose synthetic medium. In the batch fermentation, either in Erlenmeyers or in the fermentor, the pH of the culture medium was decreased rapidly from its initial pH value of 5.5 to the self-stabilized final value of 2.5 within 24 h. Experiments on the effect of initial pH on the fermentation revealed that at very low initial pH values, such as at pH 2, the polysaccharide production was in-significant. However, the biomass concentration obtained was very high at this very low initial pH value. This interesting phenomenon was served as the basic principle for the development of the bistaged pH fermentation process for the production of pullulan. In this process the first stage of fermentation was conducted at the very acidic pH for the best production of biomass. When the biomass concentration reached its maximum value, the second stage of fermentation was initiated by adjusting the medium pH to a higher value for promoting the synthesis of the polysaccharide. Experiments conducted in Erlenmeyers and in the fermentor confirmed this concept. The bistaged pH process enhanced the polysaccharide concentration in the medium, influenced the rheological properties of the fermentation broth, and has a potential of operation under nonsterile and nonaseptic conditions.

Journal ArticleDOI
TL;DR: The best mode of fermentation was a semicontinuous fed‐batch fermentation where one‐half of the fermented material was removed at three‐day intervals and replaced by fresh substrate, and protein production was 20% higher than in batch mode, protein productivity was maintained over 12 days, and sporulation was prevented.
Abstract: Optimal conditions for solid substrate fermentation of wheat straw with Chaetomium cellulolyticum in laboratory-scale stationary layer fermenters were developed. The best pretreatment for wheat straw was ammonia freeze explosion, followed by steam treatment, alkali treatment, and simple autoclaving. The optimal fermentation conditions were 80% (w/w) moisture content; incubation temperature of 37°C; 2% (w/w) unwashed mycelial inoculum; aeration at 0.12 L/h/g; substrate thickness of 1 to 2 cm; and duration of three days. Technical parameters for this optimized fermentation were: degree of substance utilization, 27.2%; protein yield/substrate, 0.09 g; biomass yield/bioconverted substrate, 0.40 g; degree of bioconversion of total available sugars in the substrate, 60.5%; specific efficiency of bioconversion, 70.8%; and overall efficiency of biomass production from substrate, 42.7%. Mixed culturing of Candida utilis further increased biomass production by 20%. The best mode of fermentation was a semicontinuous fed-batch fermentation where one-half of the fermented material was removed at three-day intervals and replaced by fresh substrate. In this mode, protein production was 20% higher than in batch mode, protein productivity was maintained over 12 days, and sporulation was prevented.

Journal ArticleDOI
TL;DR: Cellulose samples from cotton and wood pulps with varying low degrees of crystallinity (mechanically decrystallized) were studied and revealed some recrystallization during enzymatic hydrolysis which probably occurs simulataneously with a selective enzyme attack on the amorphous regions of cellulose.
Abstract: Cellulose samples from cotton and wood pulps with varying low degrees of crystallinity (mechanically decrystallized) were studied. The influence of initial cellulose crystallinity on sugar yield after enzymatic hydrolysis was determined by two different methods. As expected, samples with low crystallinity were much more accessible to enzymatic attack and glucose yields were higher than were samples of high initial crystallinity. Hydrolysis of cellulose seems more dependent on cellulose crystallinity than on the source of cellulose. It is known that decrystallized or amorphous cellulose can recrystallize under proper conditions, e.g., during acid hydrolysis. The data reported here also reveal some recrystallization during enzymatic hydrolysis which probably occurs simulataneously with a selective enzymatic attack on the amorphous regions of cellulose. In all cases, the amorphous celluloses recrystallized in the original lattice form, that of native cellulose.