bluuebunny/crossref_metadata_2025 huggingface dataset:
The enzymatic hydrolysis and fermentation of pretreated wheat straw to ethanol
Authors: Szczodrak Janusz
Published: December 2004

Autohydrolysis and ethanol‐alkali pulping were used as pretreatment methods of wheat straw for its subsequent saccharification by Trichoderma reesei cellulase. The basic hydrolysis parameters, i.e., reaction time, pH, temperature, and enzyme and substrate concentration, were optimized to maximize sugar yields from ethanol‐alkali modified straw. Thus, a 93% conversion of 2.5% straw material to sugar syrup containing 73% glucose was reached in 48 h using 40 filter paper units/g hydrolyzed substrate. The pretreated wheat straw was then fermented to ethanol at 43°C in the simultaneous saccharification and fermentation (SSF) process using T. reesei cellulase and Kluyveromyces fragilis cells. From 10% (w/v) of chemically treated straw (dry matter), 2.4% (w/v) ethanol was obtained after 48 h. When the T. reesei cellulase system was supplemented with β‐glucosidase from Aspergillus niger, the ethanol yield in the SSF process increased to 3% (w/v) and the reaction time was shortened to 24 h.
Kinetics and mathematical modeling of homoacetic fermentation of lactate by Clostridium formicoaceticum
Authors: Yang S. T. , Tang I. C. , Okos M. R.
Published: December 2004

Fermentation kinetics of Clostridium formicoaceticum grown on lactate at pH 7.0 and 35°C was studied. Acetate was the only fermentation product and its production was growth associated. The growth of this bacterium was insensitive to the lactate concentrations studied, but was inhibited by acetic acid. A Monod‐type expression with product inhibition similar to the noncompetitive inhibition of enzyme kinetics was used to model the batch fermentation. An integrated equation was developed and used to help estimating the kinetic parameters in the model. This mathematical model can be used to simulate the homoacetic fermentation of lactate by C. formicoaceticum at pH 7.0 and 35°C.
Large‐scale production of monoclonal antibodies in suspension culture
Authors: Backer M. P. , Metzger L. S. , Slaber P. L. , Nevitt K. L. , Boder G. B.
Published: December 2004

Monoclonal antibodies are being manufactured for clinical trials in suspension culture at the 1300‐L scale. Suspension culture offers some advantages relative to high‐density mammalian cell culture methods; in particular, the ability to closely monitor the behavior of cells in a homogeneous environment. Computer control and on‐line mass spectrography of exit gases provide instantaneous information about the culture metabolic activity. Air sparging and agitation by marine impeller provide aeration sufficient to maintain a constant dissolved oxygen tension at cell concentrations up to 5.0 × 106 cells/mL without causing apparent cell damage.
Serial propagation of mammalian cells on gelatin‐coated microcarriers
Authors: Tao Teh‐Yi , Ji Guang‐Yong , Hu Wei‐Shou
Published: December 2004

The ability to serially propagate mammalian cells in microcarrier cultures is essential for large‐scale operation. The success of such serial propagation depends on viable dissociation of cells from microcarriers and the normal growth and product formation after subsequent reinoculation. The high pH treatment developed for dissociating cells from DEAE‐derivatized microcarriers was not as effective for a number of cell strains cultivated on gelatin‐coated microcarriers. By prewashing the cell‐laden microcarriers with buffer containing a chelating agent, bovine kidney cells, BK, human embryonic foreskin fibroblasts, FS‐4, and continuous human kidney cells, TCL‐598 which produces prourokinase, were viably dissociated from commercially available gelatin‐coated microcarriers, Cytodex‐3. Cells dissociated from microcarriers reattached and grew on micro‐carriers subsequent to inoculation into subcultures. However, after subculturing, cells may attach at different rates to newly added beads and to conditioned microcarriers which cells had previously grown. It resulted in an uneven cell distribution on microcarriers and inferior growth kinetics. This effect was more profound for BK and FS‐4 cells which are propagated with a low multiplication ratio. Specifically, BK cells attach to conditioned beads at a faster rate than to new beads, while FS‐4 cells attach to new beads faster than to conditioned beads. Thus, for these two cell strains, a separator was used to separate the microcarriers from the suspension of dissociated cells before subsequent inoculation. For TCL‐598 cells, which are propagated at a high multiplication ratio, this dissociation technique can be applied directly without the separation of dissociated cells and conditioned microcarriers. All the three cell lines tested exhibit normal growth kinetics in serial propagation on microcarriers. Furthermore, the production of prourokinase by TCL598 cells serially propagated on microcarriers was comparable to that inoculated from roller bottles.
Mass transfer in a rectangular air‐lift reactor: Effects of geometry and gas recirculation
Authors: Siegel Marc H. , Merchuk Jose C.
Published: December 2004

The interrelationships between the three parts of the air lift reactor, the riser, the downcomer, and gas–liquid separator, were examined with relation to the overall mass transfer in the reactor. This involved studying the mass transfer of oxygen from the gas phase to the liquid phase for 20 different reactor geometries. Both one‐ and two‐sparger systems were studied. It was demonstrated that the gas–liquid separator plays a major role in reactor behavior and must be considered in reactor design. It was found that the overall reactor mass transfer coefficient KLA could be correlated to the pneumatic power of gas input per total dispersion volume (P/VD) and to the true riser superficial gas velocity JGR for all experimental conditions examined. The KLA is directly related to the P/VD with an exponent of approximately 1. “Two‐sparger” systems, where an auxiliary gas sparger is placed near the downcomer entrance, have higher ab solute values for KLA than single‐sparger systems.
The kinetics and mechanism of shear inactivation of lipase from Candida cylindracea
Authors: Lee Yuan‐Kun , Choo Choon‐Liang
Published: December 2004

Shearing experiments were conducted in a stirred tank reactor with 0.1% lipase solutions of Candida cylindracea. Inactivation of the lipase solutions were observed at various shear rates from 50 to 150 s−1 after continuous shearing for ca. 30‐240 min under optimal pH and temperature conditions. However, there was no shear stress denaturation of the lipase when it was subjected to shear stresses of 0.72‐109.2 kg/m/s2 and shear rate of 100 s−1. In the presence of polypropylene glycol, the rate of denaturation of the lipase decreased by 93%. When the lipase solution was filled to the brim, the rate of denaturation of the lipase decreased by 97% compared to that when reactor was half‐filled. The rate of denaturation of the lipase decreased by 61% when probes in the fermentor were removed. There was no significant difference in the rate of denaturation of the lipase under ambient conditions compared with that in the absence of oxygen, or in the absence of free metal ions. Recovery of lipase activity from the first hour of shearing was observed at a shear rate of 150 s−1. The native lipase and the lipase which had recovered its activity showed similar pH profiles, temperature profiles, and activation energies. Temperature was found to have no effect in the rate of shear‐induced denaturation of the lipase in the range 20 to 30°C during shearing at 100 s −1and optimal pH. Above 30°C, the rate of denaturation of the lipase increased drastically as a function of temperature. The significance of the findings in the de sign of reactor systems for hydrolysis or esterification of oils by lipase will be discussed.
The use of the maharanobis and modified distances for the improvement of simulation of glutamic acid production
Authors: Kishimoto Michimasa , Alfafara Catalino G. , Nakajima Mikio , Yoshida Toshiomi , Taguchi Hisaharu
Published: December 2004

A modified simulation procedure based on a statistical approach was investigated. The procedure predicts the time course of fed‐batch culture for glutamic acid production by a temperature‐sensitive strain of Brevibacterium flavum. The statistical approach requires only a data base of state points obtained in experiments, and not perfect identification of fermentation models. The simulation procedure is based on regression analysis to estimate specific rate parameters of system equations using the data points selected with reference to the Euclid distance. It was modified in that the data selection procedure included the use of the Maharanobis distance as well as a modified distance defined in this study. Simulation results using the modified procedure allow reasonable prediction of the time course of fed‐batch culture for glutamic acid compared to that involving the Euclid distance alone.
Estimating cell and product yields
Authors: Andrews G.
Published: December 2004

The balance equations for carbon, reduction potential, and energy during cell growth and product formation are rederived in a general form. Cells are treated simply as a very complex product, and the YATP concept is extended to products. Limitations on the theoretical yield are discussed for different product types. Simple aerobic products cannot be energy limited unless the maintenance requirement is large, while complex products cannot be reduction limited. A maximum yield is defined for products much more oxidized than their substrate (carbon limited) because the theoretical yield conditions may violate the energy balance. For reduced complex products the yield on available electrons is related to YATP, the P/O ratio, and the product composition. Narrow bounds are established on the actual yields in simple anaerobic fermentations, and the significance of the yields in the linear growth equation is discussed.
Immobilization of endo‐polygalacturonase from Aspergillus niger on various types of macromolecular supports
Authors: Pifferi Pier Giorgio , Tramontini Maurilio , Malacarne Alberto
Published: December 2004

Endo‐polygalacturonase (endo‐PG) was immobilized on a wide range of natural and synthetic macromolecular supports and their modified derivatives representing many chemical classes, including esters, amides, phenols, alkyl‐ and arylamines, and carboxyl derivatives. The immobilization entailed methods of adsorption alone as well as covalent bond formation using glutaraldehyde or carbodiimide or via the diazo‐coupling reaction. The most promising system proved to be immobilization on trimalehylchitosan (TMC) via adsorption followed by treatment with glutaraldehyde (GA). The binding capacity of the support is on the order of 13,000 IU/g, half of which is active. Various properties of immobilized endo‐PG were evaluated. The optimum pH of the enzyme shifted to the alkaline side. The relative catalytic activity was considerably high even at room temperature and remained so above 70°C. The thermal stability at pH 3‐4 was notably improved by immobilization, the half‐time doubling. Finally, the apparent Km was greater for immobilized endo‐PG than for native enzyme, while the Vmax was smaller for the immobilized enzyme.
High enthalpy and low enthalpy death in Saccharomyces cerevisiae induced by acetic acid
Authors: Pinto Isabel , Cardoso Helena , Leão Cecélia , van Uden N.
Published: December 2004

Acetic acid at concentrations as may occur during vinification and other alcoholic yeast fermentations induced death of glucose‐grown cell populations of Saccharomyces cerevisiae IGC 4072 at temperatures at which thermal death was not detectable. The Arrhenius plots of specific death rates with various concentrations of acetic acid (0–2%, w/v) pH 3.3 were linear and could be decomposed into two distinct families of parallel straight lines, indicating that acetic acid induced two types of death: (1) High enthalpy death (HED) predominated at lower acetic acid concentrations (> 0.5%, w/v) and higher temperatures; its enthalpy of activation (ΔH≠) approached that of thermal death (12.4 × 104 cal/mol); (2) Low enthalpy death (LED) predominated at higher acetic acid concentrations and lower temperatures with ΔH≠ of 3.9 × 104 cal/mol. While the ΔH≠ values for HED induced by acetic acid were similar with those reported earlier for HED induced by other fermentation endproducts, the values for the entropy coefficients were different: 127–168 entropy units mol−1L for acetic acid as compared with 3.6–5.1 entropy units mol−1L for ethanol, which agreed with experimental results indicating that acetic acid is over 30‐times more toxic than ethanol with respect to yeast cell viability at high process temperatures.
Automatic on‐line growth estimation method for outdoor algal biomass production
Authors: Guterman H. , Ben‐Yaakov S. , Vonshak A.
Published: December 2004

An on‐line measuring procedure for estimating productivity in outdoor algal cultures was developed and tested experimentally. The procedure is based on a previously described method for on‐line measuring net O2 production rate (OPR). The data obtained by this method was found to correlate well with the conventional procedures for estimation productivity by measuring the changes in biomass concentration in the culture. The new procedure seems to be superior to the latter since it can be carried out in an almost continuous way and can give immediate indication on the productivity. OPR could be used to monitor on‐line the photosynthetic and/or respiration activity in small research fermentors or in large‐scale open systems outdoors.
Oxidation of benzyl alcohol by whole cells of Pichia pastoris and by alcohol oxidase in aqueous and nonaqueous reaction media
Authors: Duff Sheldon J. B. , Murray William D.
Published: December 2004

The low substrate specificity of alcohol oxidase from Pichia pastoris makes this enzyme system of potential biotechnological interest. Whole cells of Pichia pastoris are able to oxidize benzyl alcohol to benzaldehyde in aqueous reaction media. The low water solubility of the reactant and product of this bioconversion, combined with the ability of both to strongly inhibit the reaction, favor the use of nonaqueous reaction fluids. Purified alcohol oxidase was shown to function in a number of 2‐phase reaction systems of varied aqueous to organic phase ratios (0.01–0.05 v/v). The apparent Vmax and Km were 5.26 g/Lh and 7.41 g/L respectively, for the oxidation of benzyl alcohol to benzaldehyde in hexane containing 3% aqueous phase. The volume of the aqueous phase had a strong effect on the reaction, with an aqueous: organic ratio of 3–5% found to be optimum. The enzyme could be firmly immobilized on DEAE‐Biogel (Biorad) to enhance stability and biocatalyst recovery.
On‐line analysis of avermectin fermentation cell growth kinetics in an industrial pilot plant
Authors: Gbewonyo K. , Jain D. , Hunt G. , Drew S. W. , Buckland B. C.
Published: December 2004

Experimental data are presented which show that on‐line calculation of oxygen uptake rate can be used to estimate the cell concentration of Streptomyces avermitilis during the active growth phase of this fermentation. Moreover, by dividing the oxygen uptake rate by the total oxygen consumed, an on‐line estimate of specific growth rate of this culture can be generated. A theoretical basis is provided for this model. Use of a mass spectrometer for vent gas analysis coupled with computer data acquisition has made this information both very accurate and readily available. Examples are given which illustrate the kinetics of the avermectin fermentation as well as the effect of a temperature shift on the specific growth rate.
Characteristics of tyrosinase in AOT–isooctane reverse micelles
Authors: Bru Roque , Sanchez‐Ferrer Alvaro , García‐Carmona Francisco
Published: December 2004

Isooctane–AOT–H2O is a suitable system for studying enzyme behavior in organic solvents. Tyrosinase was able to catalyze a well‐known reaction in aqueous medium: oxidation of 4‐methylcatechol to yield 4‐methyl‐o‐benzoquinone. This reaction was studied using the preceding ternary system with adequate amounts of each component to make up reverse micelles. 4‐Methyl‐o‐benzoquinone stability was demonstrated in isooctane even at alkaline pH values. Apparent Km and Vmax were similar to those in water, but substrate inhibition was more evident. The pH and temperature appear to be shifted toward high and low values, respectively. Characteristic parameters of reverse micelles, ω0 (= H2O/AOT) and percentage of H2O (v/v), were investigated. The results obtained showed that the steady‐state rate varies either with ω0 or with percentage of H2O. The variation observed with ω0 showed an optimal value while an increase in percentage of H2O can lead to decreased or increased activity depending on substrate concentration.
A flow injection analysis system for fermentation monitoring and control
Authors: Garn Morten , Gisin Marcus , Thommen Christian , Cevey Pierre
Published: December 2004

An automated analysis system for on‐line fermentation monitoring is presented. The modular system consists of an in‐line sterilizeable crossflow microfilter, a selection valve that allows injection of sample or standards, a degassing unit, a dilution module, and a FIA manifold with a spectrophotometric UV/VIS detector. In the dilution module samples are conditioned and diluted depending upon concentration of analyte and the working range of the analyzer. Methods for the monitoring of glucose, ethanol, ammonia and phosphate are described. Results from the monitoring of glucose and their use in fermentation control are presented. The maximal analysis frequency is 30 samples per hour including the dilution of 1 : 200. Detection limits are 5 mg/L for ethanol and glucose, 1 mg/L for phosphate and 50 mg/L for ammonia.
Cross‐flow membrane microfiltration of a bacteriol fermentation broth
Authors: Nagata Naohiko , Herouvis Kay J. , Dziewulski David M. , Belfort Georges
Published: December 2004

Although cross‐flow membrane filtration is a very attractive option for harvesting cells and recovering enzymes from cell homogenates, the process is not without its problems. Foremost of these is the deposit of dissolved and suspended solutes onto the membrane surface during operation. The formation of these dense and sometimes compressive sublayers (often called cakes) offers additional resistance to axial and permeate flows and often affects the retention characteristics of the process. In view of the complex nature of the sublayer formation process and its sensitivity to cross‐flow velocity, this investigation was undertaken to determine the main factors responsible for the decline in performance during the harvesting of B. polymyxa broth by membrane microfiltration. System parameters varied include axial flow rate, concentration of cells, proteins and other components in the feed, membrane materials (ceramic, polypropylene, and stainless steel), and cleaning methods. To help explain the observed results, a new mass transport model—the solids flux model—based on the assumptions that back migration of particles from the sublayer or membrane surface is negligible and that particles that reach the solid–solution interface attach (stick) completely, is tested. Using a variety of diagnostic methods, magnesium ammonium phosphate precipitate is formed during steam sterilization of the medium and is implicated as the major foulant in this study.
Improvement of proteolytic resistance of immunoadsorbents by chemical modification with polyethylene glycol
Authors: Kondo Akihiko , Kishimura Masaaki , Katoh Shigeo , Sada Eizo
Published: December 2004

Immunoadsorbents were modified with monomethoxy‐polyethylene glycol (PEG; average molecular weights of 5000 (PEG‐5000) and 1900 (PEG‐1900)) activated with cyanuric acid (activated PEG) by four different methods. In the two methods, anti‐BSA antibodies were modified with activated PEG with and without protection of antigen binding sites with BSA and then were coupled to CNBr‐activated Sepharose 4B. In the other two methods, Immunoadsorbents, which were prepared by coupling anti‐BSA antibodies to CNBr‐activated Sepharose 4B, were modified with activated PEG with and without the protection. The effects of PEG modification by these four methods on the binding ratio (the ratio of the numbers of moles of antigen adsorbed to the numbers of moles of binding sites of antibody coupled), the antigen binding property and the resistance to proteolytic digestion of immunoadsorbents were studied. The decrease in the binding ratio by the modification with activated PEG was small enough to use modified immunoadsorbents for industrial purification processes. The resistance to proteolytic digestion of immunoadsorbents was improved by modification with activated PEG. The modification without protection of antigen binding sites gave higher resistance to proteolytic digestion than that with protection, while the former caused larger decrease in the binding ratio of modification. The immunoadsorbents modified with activated PEG‐5000 showed higher resistance to proteolytic digestion than those modified with activated PEG‐1900.
Transcription from plasmid genes, macromolecular stability, and cell‐specific productivity in Escherichia coli carrying copy number mutant plasmids
Authors: Peretti S. W. , Bailey J. E. , Lee James J.
Published: December 2004

Experiments were performed to evaluate, qualitatively and quantitatively, the adaptation of Escherichia coli to plasmid maintenance and cloned gene expression. Experimental findings indicate that the metabolic response to low plasmid levels is an increase of the biosynthetic capacity of both transcription and translation. At high copy number levels the gene‐specific transcription rate continues to increase but the stability of plasmid‐derived mRNA drops sharply. Protein levels are maintained, but translation efficiency decreases. These results indicate that cellular biosynthetic capacity may not be limiting productivity in recombinant systems. If macromolecular stability is the bottleneck, then current efforts to increase gene expression that focus on enhancing synthesis rates will be ineffective.
Covalent immobilization of lipase in organic solvents
Authors: Stark Maj‐Britt , Holmberg Krister
Published: December 2004

Lipase from Rhizopus sp. has been immobilized covalently on tresyl activated silica. Three different coupling media were evaluated: aqueous buffer, n‐hexane, and a microemulsion based on n‐hexane, aqueous buffer, and the nonionic surfactant triethylene glycol monododecyl ether. In addition, coupling via a very long, hydrophilic spacer arm, polyethylene glycol 1500 (PEG 1500), was compared with attachment to the silica via a short silane bridge only. The enzyme preparations were tested in hydrolysis and transesterification reactions. In the hydrolysis no marked differences in activity were found between the coupling media used. In the transesterification, on the other hand, the choice of immobilization medium had a very large effect on lipase activity, the preparation from microemulsion being the most active one. The use of the hydrophilic spacer had a large effect on activity in the hydrolysis reaction. Whereas direct coupling gave an activity of immobilized lipase of 26–34% of that of free enzyme, depending on the reaction medium, lipase bound via the spacer exhibited 56–67% activity. The latter values are considerably higher than previously reported in the literature for covalently immobilized lipase. The hydrophilic spacer had no effect on enzyme activity in the transesterification, however, a fact which is attributed to the hydrophobic medium of this reaction. The spacer is incompatible with the reaction medium and will, therefore, adsorb on the particles rather than stretch out into the bulk phase. The stability of the bound lipase was extremely good, no loss in activity being observed after a period of three weeks in aqueous solution of 37°C.
Growth of microbial populations in nonminimal media: Some considerations for modeling
Authors: Pavlou Stayros , Fredrickson A. G.
Published: December 2004

Ramkrishna and his co‐workers have developed so‐called cybernetic models which purport to describe, among other things, how microorganisms make choices when presented with two or more functionally equivalent, or substitutable, nutrients that are sources of carbon and available energy. In general, however, organisms are presented with choices not just between nutrients that are substitutable for one another, but also between sets of nutrients some of which are by no means substitutable for one another. It is postulated herein that the main ideas of cybernetic modeling apply to these more general choices as they seem to apply to the choices considered by Ramkrishna and his co‐workers. Some consequences of the postulate are worked out for steady‐state growth situations where two, or in one case three, nutrients limit or potentially limit growth rate. If predicted phenomena are observed experimentally so as to verify the postulate, a significantly improved basis for understanding growth of microorganisms in practical fermentation media as well as in natural situations will be provided by this application of cybernetic modeling ideas.
Growth and gas production for hyperthermophilic archaebacterium, Pyrococcus furiosus
Authors: Malik B. , Su W.‐w. , Wald H. L. , Blumentals I. I. , Kelly R. M.
Published: December 2004

Pyrococcus furiosus represents one of the most important hyperthermophilic bacteria isolated thus far because of its relatively high cell yields and rapid growth rates. Pyrococcus furiosus exhibits several interesting growth characteristics, especially in terms of biotic gas production, which were examined in this study. In the presence of elemental sulfur, both carbon dioxide and hydrogen sulfide production appeared to be strongly growth associated, while no significant hydrogen production was observed. In the absence of sulfur, hydrogen and carbon dioxide were produced by the organism and hydrogen inhibition was observed. The addition of elemental sulfur to the medium apparently eliminated, hydrogen inhibition as growth proceeded normally even when hydrogen was added to the gas phase. Also, no apparent substrate limitation or toxic product could be attributed to the cessation of growth as cell growth in spent media was at least as good as in fresh media. An unstructured growth model was used to correlate growth and gas production for P. furiosus in complex seawater‐based media at 98° C both in the absence and presence of elemental sulfur. The model was shown to be useful for examining some of the observations made in this study.
Microfiltration cell‐recycle pilot system for continuous thermoanaerobic production of exo‐β‐amylase
Authors: Nipkow André , Zeikus J. Gregory , Gerhardt Philipp
Published: December 2004

A microfiltration cell‐recycle pilot‐scale system was developed comprised of a conventional continuous‐flow fermentor connected to an in situ steam‐sterilizable cross‐flow ceramic filter with a backflushing device. A microcomputer was used to control filtration pressure, tangential flow velocity, and backflushing. Performance of the system was tested with the anaerobic production of thermostable extracellular β‐amylase at 60°C by Clostridium thermosulfurogenes on maltose or malto‐dextrin media. Filtration rates during continuous cultivation were between 20 and 60 L/m2/h. The maltodextrin and cell debris occurring at high retentate flow rates or filtration pressures impaired the performance of the filter. Backflushing initially improved the permeate flux to 42% in a maltose medium and to 10% in a maltodextrin medium, but the effect diminished with time. The productivity of β‐amylase (as much as 48 U/mL/h) and concentration of biomass (as much as 14 g/L) were increased 11‐ and 12‐fold, respectively, if compared to values obtained in a chemostat. The concentration of β‐amylase rose to 220 U/mL in the reactor, which was 5.5‐fold more than under comparable conditions in a chemostat.
A new isolation and purification method for staphylococcal protein A using membrane encapsulated rabbit IgG‐agarose
Authors: Sakoda Akiyoshi , Wang Henry Y.
Published: December 2004

A new isolation and purification method for bioproducts using membrane‐encapsulated affinity adsorbents was investigated. The new method involves encapsulation of affinity adsorbents, batch adsorption of the bioproduct from whole fermentation broth and rapid batch desorption after dissolution of the capsule membranes. Recovery of protein A from Staphylococcus aureus was used as the model experimental system. Affinity adsorbents such as rabbit IgG‐agarose were successfully encapsulated within calcium alginate membranes and used directly to recover protein A from whole cell homogenate containing a number of macromolecular contaminants as well as suspended solids. Both high yield and high purity of protein A were recovered by this method in comparison with various previously reported methods.
Measurement of KLa by a gassing‐in method with oxygen‐enriched air
Authors: Chang Ho Nam , Halard Benoit , Moo‐Young Murray
Published: December 2004

The dynamic gassing‐out method using nitrogen for gas–liquid KLa measurements has been modified so that gassing‐out is performed with air and gassing‐in with oxygen‐enriched air. This new method was proven theoretically valid for use in inert model systems and in actual fermentation systems. The KLa values were measured in a 1‐m‐high bubble column and compared with those obtained from the traditional gassing‐in method for three different mixing models in batchwise contacting: mixed gas and liquid (MMB); plug‐flow gas and mixed liquid (PMB); and plug‐flow gas and plug‐flow liquid (PPB). The KLa values obtained from the new method were consistent with those of the method of Bartholomew et al. Discrimination between the models appeared to be not important for the 1‐m‐high column, but the theoretical analysis revealed that it would become necessary for columns about 10 m and higher.
Culture of photomixotrophic soybean and pine in a modified fermentor using a novel impeller
Authors: Treat W. J. , Engler C. R. , Soltes E. J.
Published: December 2004

Photomixotrophic suspensions of Glycine max (soybean) and Pinus elliottii (slash pine) have been successfully cultured in a hybrid stirred tank photobioreactor using a novel cell‐lift impeller. A cell‐lift impeller exhibited cell viabilities over 90% and an average cell aggregate size of 1.0 mm or less. Flat‐bladed turbines produced equivalent biomass to the cell‐lift impeller, but cell viability was reduced (85%) and cell aggregate size increased (3–5 mm diameter). Maximum fresh weights of 82 g L−1 (soybean) and 52 g L−1 (slash pine) were achieved in 15 days using continuous lighting (90–100 μE m−2 s−1) and supplemental 2% CO2 inlet gas. Maximum biomass was achieved using an impeller speed of 60 rpm with air‐flow rate of 0.2 vvm for the cell‐lift impeller and the pair of flat bladed turbines. The lag and early exponential phases were characterized by (1) rapid hydrolysis of sucrose followed by preferential use of glucose and (2) a reduction in chlorophyll levels. Carbon dioxide (2%–5%) was an essential nutrient for photomixotrophic cell culture in the bioreactors.
Influence of dilution rate on the acidogenic phase products distribution during two‐phase lactose anaerobiosis
Authors: Kisaalita W. S. , Lo K. V. , Pinder K. L.
Published: December 2004

Acidogenic fermentation of lactose was carried out in a continuous stirred reactor with a mixed anaerobic culture. From the variation of the reactor products with pH and dilution rate two possible carbon flow schemes were proposed for the reaction. In both schemes the carbon flow from pyruvate to butyrate and lactate was assumed to occur in parallel. A change in gas composition and in product concentrations at dilution rates between 0.1 and 0.15 h−1 for pH levels between 4.5 and 6.0 was ascribed to a shift in microbial population. To clarify the mechanism radiotracer tests were made using [U–14C]‐butyrate, [2–14C]‐propionate and [U–14C]‐lactate to determine the path of carbon flow during acidogenesis of lactose using a mixed culture. At a dilution rate between 0.1 and 0.15 h−1 and pH from 4.5 to 6.0 a rise in the lactate concentration in the product was shown to be due to a microbial population shift which disabled the conversion of lactate to other intermediary metabolites. It was also found that the flow of carbon from pyruvate to butyrate and lactate occurred by parallel pathways. Also, in the presence of hydrogen reducing methanogens, lactate was almost completely converted to acetate and not propionate. Butyrate was found to be converted to acetate at a slow rate as long as hydrogen reducing methanogens were present. The role played by propionibacteria in this lactose acidogenic eocosystem was minor. From the carbon flow model it can be concluded that lactate is the most suitable marker for optimizing an acidogenic reactor in a two‐phase biomethanation process.
Fast inferential adaptive optimization of a continuous yeast culture based on carbon dioxide evolution rate
Authors: Chang Yong K. , Lim Henry C.
Published: December 2004

A fast inferential, multivariable adaptive optimization algorithm based on a fast responding off‐gas data, the carbon dioxide evolution rate (CER), has been developed and applied to a continuous baker's yeast culture to maximize the cellular productivity in simulation and experimental studies. In the simulation study the process was optimized based on CER measurements using readily available steady‐state data on the ratio between the cellular productivity and the CER. It was shown that the algorithm is two to three times faster than the algorithm based on cell mass concentration measurements. In the experimental study the CER was maximized without any information on the relationship between the cellular productivity and the CER. It took about 40 h for the process to converge, while about 80 h was required when the optimization was based on cell mass measurements. The attained steady state was found to be different but fairly close to that obtained with cell measurements. Briefly discussed is a switching to the cell‐mass‐based algorithm at the final stage of the optimization to overcome a potential inaccuracy.
Optimization of sulphur production in a biotechnological sulphide‐removing reactor
Authors: Buisman Cees J. N. , Geraats Bert G. , Ijspeert Peter , Lettinga Gatze
Published: December 2004

A new biotechnological process for sulphide removal is proposed. The principle of this process is that sulphide is converted into elemental sulphur, which can be removed by sedimentation. In this article, investigations on the optimization of the sulphur production are reported. It seems that less than 10% sulphate is produced at low oxygen concentration, when the sulphide concentration in the reactor exceeds 10 mg/L. At sulphide concentrations higher than 20 mg/L only 5% of the incoming sulphide is converted to sulphate even at high oxygen concentrations. An immobilized biomass on recticulated polyurethane produced more sulphate than a free cell suspension at the same oxygen and sulphide concentration.
A mathematical model for examining growth and sporulation processes of Bacillus subtilis
Authors: Jeong J. W. , Snay J. , Ataai M. M.
Published: December 2004

A mathematical model for the growth process of the bacterium Bacillus subtilis is described. The model is a highly structured one. The driving motivation for development of the model and explicit accounting of major interactions of metabolic networks in the model is related to our eventual goal that the model will be used in the analysis of complex biological patterns. Bacillus subtilis was chosen in our study due to the interesting sporulation process that these cells undergo in response to adverse environmental conditions including nutrient limitation. Sporulation process in B. subtilis represents a primordial prototype of cellular differentiation in higher cellular systems. Thus a model for the B. subtilis growth process should prove extremely useful for understanding questions of developmental biology. The model is capable of simulating the transition between the exponential and stationary phase of growth in a batch culture. Since during the transition period the growth process and the metabolism become decoupled and many transient processes are taking place, such predictions are a severe test for the validity of any model. A strategy to examine the leading hypothesis on B. subtills sporulation implementing GTP as a component which signals sporulation initiation is described.
A general model for aerobic yeast growth: Batch growth
Authors: Barford J. P.
Published: December 2004

A general model for aerobic yeast growth in batch culture is presented. It is based on the concept that the aerobic metabolism of all yeasts is determined by the relative sizes of the transport rate of sugar into the cell and the transport rate of respiratory intermediates into the mitochondrion. If the rate of sugar uptake rate exceeds the rate of transport of respiratory intermediates into the mitochondrion (as in Saccharomyces cerevisiae, S. uvarum, and S. pombe), the metabolism exhibits the features of ethanol excretion and limited specific oxygen uptake rate. If the rate of transport of respiratory intermediates into the mitochondrion is of the same order as the transport of sugar into the cell (as in Candida utilis), the metabolism is characterized by little or no ethanol excretion and a much higher specific oxygen uptake rate. Batch data from an extensive range of yeast and carbon sources is used to illustrate the use of this model. The ability of this model to fit such an extensive range of experimental data suggests that it can be used as a generalized model for aerobic yeast growth.
A general model for aerobic yeast growth: Continuous culture
Authors: Barford J. P.
Published: December 2004

A general model for the aerobic growth of yeast in continuous culture is presented. The model is capable of simulating the complete range of metabolic responses observed for yeast growth in continuous culture including respiratory repression, saturated respiratory capacity, and respiratory depression.

It is postulated that respiratory depression is the result of the adaptation (increase in capacity of the respiratory intermediate transport proteins located at the mitochondrial membrane). Respiratory repression and subsequent saturated respiratory capacity is postulated to be the result of the gradual transfer of biosynthetic intermediates provision from the mitochondrion to the cytoplasm or, possibly, the adaptation (increase) in the capacity of the cell to excrete ethnol. It is difficult to provide a definitive experimental verification of these postulates.

Irrespective of the biochemical basis of respiratory repression and depression, the model described is capable of simulating the complete range of metabolic responses obtained for yeast growth in continuous culture. It is the only model reported in the literature capable of achieving this.
Use of an oxygen microsensor for the determination of intrinsic kinetic parameters of an immobilized oxygen reducing enzyme
Authors: Hooijmans C. M. , Geraats S. G. M. , Luyben K. Ch. A. M.
Published: December 2004

An oxygen microsensor was used to measure internal oxygen profiles in biocatalyst particles of different diameter and activity. The particles were made of agarose gel and contained an oxygen reducing enzyme, L‐lactate mono‐oxygenase. The kinetics of the enzyme could be well described by the Michaelis–Menten equation. From the internal substrate concentration profile the intrinsic kinetic parameters were determined by means of fitting a simulated profile to the measurements, using Marquardt's algorithm. The intrinsic kinetic parameters found following this procedure appeared to be independent of particle radius or enzyme loading used, proving the method to be reliable. These parameters were also compared with the kinetic parameters of the free enzyme which were determined in a biological oxygen monitoring system. The intrinsic kinetic parameters showed a decrease with a factor 2.3 for Vm value and with a factor 2.7 for the Km value compared to the parameters for the free enzyme. From this the conclusion can be drawn that the immobilization as such or the carrier material not only can have an effect on the maximum intrinsic conversion rate (Vm) but also on the affinity of the enzyme (Km) for oxygen.
Development of a strategy to control the dissolved concentrations of oxygen and carbon dioxide at constant shear in a plant cell bioreactor
Authors: Smith Jeffrey M. , Davison Stowell W. , Payne Gregory F.
Published: December 2004

To examine the effects of volatile components on plant cell growth, a bioreactor control system was developed to simultaneously control the dissolved concentrations of both oxygen and carbon dioxide. The first step in this work was to develop a mathematical model to account for gas–liquid mass transfer; biological utilization and production of O2 and CO2; and the series of chemical reactions of CO2 in water. Using this model and dynamic measurements for dissolved O2 and CO2, it was observed that (1) both absorption and desorption of a volatile component could be described by a single mass transfer coefficient, Kla, and (2) Kla values for oxygen and carbon dioxide transfer were directly proportional. The second step of this work was to employ the mathematical model in an adaptive feed‐forward strategy to control the dissolved O2 and CO2 concentrations by manipulating the inlet gas composition to the bioreactor. This strategy allowed dissolved concentrations to be controlled without the need for changing either the total gas flow rate or agitator speed. Adaptive control was required because the volumetric rates of O2 and CO2 consumption and production vary with time during long term operation and therefore these rates must be continually updated. As the final step, we demonstrated that this control strategy was capable of controlling the dissolved gas concentrations in both short‐ and long‐term studies involving the cultivation of Catharanthus roseus plant cells.
Degradation kinetics of pentachlorophenol byPhanerochaete chrysosporium
Authors: Lin Jian‐Er , Wang Henry Y. , Hickey Robert F.
Published: December 2004

The extracellular enzymes and cell mass from the pregrownPhanerochaete chrysosporiumcultures were used for the degradation of PCP. The use of both extracellular enzymes and cell mass resulted in extensive mineralization of PCP, while the action of only the crude extracellular enzymes led to the formation of a degradation intermediate (TCHD). A kinetic model, which describes the relationship among PCP degradation, initial PCP concentration, dosage of extracellular enzymes, and cell mass concentration, was developed. Based on this model, various effects of initial PCP concentration, dosage of extracellular enzymes, and cell mass concentration were evaluated experimentally. It was found that when initial PCP concentration is lower than 12 μmol/L, the model of a parallel‐series first‐order reaction is sufficient to describe the degradation process. PCP disappearance and mineralization were enhanced by increasing either the extracellular enzyme concentration or the cell mass concentration. As high as 70% of PCP mineralization could be obtained by using a higher dosage of extracellular enzymes and cell mass. Various parameters of the kinetic model were determined and the model was verified experimentally. Simulation using this model provided the criteria needed to choose rational dosages of extracellular enzymes and cell mass for the degradation of PCP. Data reported allow some insight into the function of the extracellular enzymes and cell mass ofP. chrysosporiumin degradation processes of toxic pollutants and assist in the design and evaluation of practical bioremediation methods.
Increased mass transfer to microorganisms with fluid motion
Authors: Logan Bruce E. , Dettmer James W.
Published: December 2004

The effect of fluid flow and laminar shear on bacterial uptake was examined under conditions representative of the fluid environment of unattached and attached cells in wastewater treatment bioreactors. Laminar shear rates below 50 s−1 did not increase leucine uptake by suspended cultures of Zoogloea ramigera. However, leucine uptake by cells fixed in a flow field of ∼ 1 mm s−1 was 55–65% greater than uptake by suspended cells. Enhanced microbial uptake with advective motion is consistent with mass transfer rates calculated using Sherwood number correlations. Advective flow increases microbial uptake by increasing collisions between substrate molecules and cells through compression of the concentration boundary layer surrounding a cell. The rate of leucine uptake suggests that binding proteins used to transport leucine into the cell can occupy approximately 1% of the cell surface area.
Oxidation of hydrogen sulfide by Thiobacilli
Authors: Cadenhead Patricia , Sublette Kerry L.
Published: December 2004

It has been previously demonstrated that the chemoautotroph and facultative anaerobe, Thiobacillus denitrificans, may be cultured aerobically or anaerobically in batch and continuous reactors on H2S(g) under sulfide‐limiting conditions. A process has been proposed for the removal of H2S from gases based on oxidation of H2S by T. denitrificans. Described here is a study of H2S oxidation by other Thiobacilli, the purpose of which has been to determine whether other Thiobacilli offer any advantages over T. denitrificans in the aerobic oxidation of H2S. Although four other species of Thiobacillus were found to grow on H2S as an energy source, none offer a clear advantage over T. denitrificans.
Air‐bubbling, hollow‐fiber reactor with cell bleeding and cross‐flow filtration
Authors: Nishii Kunio , Sode Koji , Karube Isao
Published: December 2004

Continuous asymmetric reduction of dyhydrooxoisophorone (DOIP) to 4‐hydroxy‐2,2,6‐trimethylcyclo‐hexanone (4‐HTMCH) was achieved by a thermophilic bacterium Bacillus stearothermophilus NK86‐0151. Three reactors were used: an air‐bubbling hollow‐fiber reactor with cell bleeding and cross‐flow filtration, an air‐lift reactor, and a CSTR with PAA immobilized cells. The maximum cell concentration of 11.1 g dry wt L−1 was obtained in an air‐bubbling hollow‐fiber reactor, while in the other reactors the cell densities were between 3.5 and 4.1 g dry wt L−1 The optimum bleed ratio was 0.1 at the dilution rate 0.3 h−1 in the hollow‐fiber reactor. The highest viable cell concentration was maintained in the dilution range of 0.4–0.7 h−1 by a combination of proper cell bleeding and cross‐flow filtration. The maximum volumetric productivity of 4‐HTMCH reached 826 mg L−1 h−1 at the dilution rate 0.54 h−1. This value was 4 and 2 times higher than those in the air‐lift reactor and CSTR, respectively. The increasing viable cell concentration increased the volumetric productivity of 4‐HTMCH. A cell free product solution was continuously obtained by cross‐flow filtration.