bluuebunny/crossref_metadata_2025 huggingface dataset:
Substituent effects on the puckering mode of the cyclobutane ring and the glycosyl bond of cis–syn photodimers
Authors: Kim Jong‐Ki , Wallace John C. , Alderfer James L.
Published: December 2004

The cyclobutane ring (CB) puckering of a cis–syn DNA photodimer (cis–syn d‐T[p]T) differs from that of a cis–syn RNA photodimer (cis–syn r‐U [p] U) [J.‐K. Kim and J. L. Alderfer (1992) Journal of Biomolecular Structure and Dynamics, Vol. 9, p. 1705]. In cis–syn d‐T [p] T, interconversion of the CB ring between CB+ and CB− is observed, while in cis–syn r‐U [p] U only CB− is observed. In the CB+ conformation, the two thymine rings of the dimer are twisted in a right‐handed fashion, as are the bases in B‐form DNA. In case of CB− they are twisted in a left‐handed fashion. The C5 (base) and/or C2′ (sugar) substituents apparently affect the CB ring flexibility in cis–syn d‐T [p] T and cis–syn r‐U [p] U. To study the effects of the C5 substituent on CB ring flexibility, two‐dimensional nuclear Overhauser effect (NOE) and 31P‐nmr experiments were performed on cis–syn d‐T [p] U, cis–syn d‐U [p] T, and cis–syn d‐U [p] U photodimers to investigate the CB puckering mode and overall molecular conformation and dynamics. The NOE results indicate the 5‐methyl group in the photodimer induces conformational flexibility of the CB ring. In cis–syn d‐T [p] U and cis–syn d‐U [p] T, both CB+ and CB− puckering modes are observed. This indicates interconversion between two modes takes place as observed in cis–syn d‐T [p] T. In the case of cis–syn d‐U [p] U, only the puckering CB− mode is observed. All three DNA‐type dimers—cis–syn d‐T [p] U, cis–syn d‐U [p] T, cis–syn d‐U [p] U—show a characteristic flexibility of glycosidic bonds at the 5′ residue; cis–syn d‐T [p] T demonstrates syn–anti interconversion for both the 3′ and 5′ sides, while the others are exclusively anti on the 3′ side. In contrast, the ribophotodimer, cis–syn r‐U [p] U, lacking the C5 methyls and having a C2′‐OH, demonstrates no conformational flexibility in the CB ring or in either of the glycosidic bonds. Differential flexibility of the three DNA‐type dimers (cis–syn d‐T [p] U, cis–syn d‐U [p] T, cis–syn d‐U [p] U) and the RNA dimer (cis–syn r‐U [p] U) in the sugar‐phosphate backbone region is also apparent from the temperature dependence of the 31P chemical shifts of these photodimers compared to their normal dimer analogues. Over the temperature range 18‐63°C, the chemical shift change is reduced 22–42% in three DNA‐type dimers, while it is reduced 71% in cis–syn r‐U [p] U, suggesting the RNA‐type dimer is more rigid. © 1993 John Wiley & Sons, Inc.
Molecular dynamics simulations of poly(dA)·poly(dT): Comparisons between implicit and explicit solvent representations
Authors: Fritsch V. , Ravishanker G. , Beveridge D. L , Westhof E.
Published: December 2004

The program AMBER 3.0 has been used to generate molecular dynamics trajectories of a poly (dA)·poly (dT) decamer. The simulations were performed using different methods to treat solvent effects. Results of a simulation including 18 counterions NH and 4109 water molecules under (N, P, T) conditions were compared to simulation runs with implicit solvent representation in which solvent screening effects were represented by the use of a sigmoidal distance‐dependent dielectric function. In the latter case, the system was simulated under microcanonical (N, V, E) and canonical (N, V, T) conditions. For the fully hydrated system simulation, a preequilibration protocol was developed since it was observed that long and progressive periods of heating and equilibration on the overall system were necessary in order to avoid energetic collisions between the solute and the solvent molecules, leading to severe irreversible deformation of the solute. A detailed analysis of DNA conformations, sugar puckers, and stability of the hydrogen bonds, Watson–Crick and three‐center H bonds, is reported. The results show that DNA remains essentially in the B conformer with a tendency in the hydrated model to adopt a slightly distorted, unwound, and stretched conformation in comparison to standard B‐DNA. Concerning sugar puckers, the mean pseudorotation phases of the adenine residues are systematically higher than those of the thymine residues, except in the case of the hydrated model for which a particular behavior is observed for the adenine strand. In this case, the terminal bases oscillate between C2′,‐endo and O4′,‐endo and the central ones stay in the C3′,‐endo domain. The mean lifetimes of the internal Watson–Crick H‐bond (A)HN6O4(T) are also dependent on the base pairs included in the calculation, excepted for the implicit solvent simulation at constant temperature. The three‐center H bonds have very small mean lifetimes in all three cases of MD simulation. In the minor groove of the hydrated model, a spine of hydration is found as observed by x‐ray crystallography and other theoretical simulations. On the basis of the rms deviations, it appears that the fully hydrated simulation has not reached a plateau at the end of the run, while the implicit simulation at constant energy seems to have converged. At constant temperature, very large oscillations in rms deviations are observed. © 1993 John Wiley & Sons, Inc.
Structural changes in 16S RNA from Escherichia coli upon unfolding by urea
Authors: Timchenko A. A. , Langowski J. , Serdyuk I. N.
Published: December 2004

The urea‐induced unfolding of 16S RNA at low ionic strength has been studied by dynamic light scattering, uv spectroscopy, and some hydrodynamic methods. Three components could be resolved in the photon correlation spectra of scattered light, using the inverse Laplace transform SIPP program [G. R. Danovich and I. N. Serdyuk (1983) in Photon Correlation Techniques in Fluid Mechanics, vol. B38, E. O. Schulz‐Dubois, Ed., Springer, Berlin/Heidelberg, New York, p. 315]. One component is assigned to the center‐of‐mass translation of the RNA, another one to a combination of translational and internal motion, and the last to diffusion of urea clusters. The hydrodynamic dimensions of RNA increase strongly upon transition from 4 to 6M urea. We conclude that up to 2M urea, 16S RNA is highly elongated, and coiled above 4M urea, with a great increase of the hydrodynamic dimensions of RNA being observed upon transition from 4 to 6M urea. A scheme for RNA unfolding is proposed. © 1993 John Wiley & Sons, Inc.
Aeration in tower‐type fermentors: Effect of tower diameter and number of aeration disks
Authors: Clark D. S.
Published: December 2004

The rate of oxygen absorption by aqueous sodium sulphite solutions in tower‐type fermentors up to 6 in. in diameter was related both to tower diameter and to the number of sintered Pyrex disks used for dispersing air entering the towers. Maximal rates of absorption were obtained in towers 2.5 in. in diameter. Under comparable conditions, rates of oxygen transfer in towers containing one aeration disk were approximately 30% higher than those in similar towers containing two or more disks. In towers greater than 6 in. in diameter, the absorption rate was independent of vessel diameter and number of aeration disks when more than one disk was used. Bubble coalescence was the main cause of the difference in the rate of oxygen absorption.
Methods for the production of mutants suitable as amino acid fermentation organisms
Authors: Karlström Olle
Published: December 2004

In order to find effective methods to isolate microorganisms that excrete large amounts of amino acids, a number of mutants of Escherichia coli ATCC 4157 were prepared and characterized. The majority were isolated for resistance to amino acid analogs. The penicillin method was also employed to select potential producer strains devoid of a biosynthetic enzyme in one case and a catabolic enzyme (tryptophanase) in another. Both of these enzymes were suspected of reducing the yield of an excerted amino acid. The identification of amino acid excreting colonies was aided by the use of pigmented auxotrophic test bacteria.

Amino acid analog resistance was frequently found to increase amino acid production. In particular, excretion of valine and glutamic acid could be achieved with comparative ease. Conditions of culture were of extreme importance for the amount and kind of amino acid produced. Under certain conditions a norvaline‐resistant strain and even better a leucine‐requiring derivative of it excreted more than 2 mg./ml. of valine into the culture medium. The acetolactate‐forming enzyme of this strain was not repressible by leucine in contrast to the same enzyme in the wild type. Reversal of the growth inhibitory effects of amino acid analogs by amino acids was studied on agar plates. This method gave too complex results to be a simple guide in the selection of analogs suitable for the isolation of a particular type of production mutant.
Purification and characterization of the amylase of B. subtilis NRRL B3411
Authors: Moseley Martha H. , Keay Leonard
Published: December 2004

The amylase of Bacillus subtilis NRRL B3411 has been purified and partially characterized. The specific activity can be increased from 300,000 units/g to 6,000,000 units/g with a 60% recovery of total units. The purified material consists of one major and one trace anodic component as determined by disc gel electrophoresis. The molecular weight was 48,000 as determined by bio‐gel filtration; the molecular weight was 44,900 ± 2400 as determined by sedimentation equilibrium methods. This purified enzyme is stable at, 70°C in the presence of 0.01 M Ca++ and 0.1 M NaCl over a broad pH range from 5.5–9.5. The pH activity profile indicates optimum activity at pH 6.0. This amylase exhibits maximum activity at 60°C. The enzyme is a liquefying α‐amylase as determined by analysis of hydrolysis products and immunological studies.
Comparative kinetic studies on the neutral protease and thermolysin catalyzed hydrolysis of simple dipeptide substrates
Authors: Feder Joseph , Schuck James M.
Published: December 2004

A comparative study of the Bacillus subtilis neutral protease and Bacillus thermoproteolyticus thermolysin calalyzed hydrolysis of a few dipeptide sustrates including furylacryloylglycyl‐L‐leucine amide is reported. While differences in the kcat/Km were observed between the two enzymes toward substrates in which phenylalanine or leucine donated the amino group of the peptide bond, secondary effects of substituents on the carbonyl donating amino acid and pH profiles were quite similar. Differences were also observed toward protein substrates as compared to dipeptides.
Dialysis fermentation. I. Enhanced production of salicylic acid from naphthalene Pseudomonas fluorescens
Authors: Abbott Bernard J. , Gerhardt Philipp
Published: December 2004

The conversion of naphthalene to salicylic acid by Pseudomonas fluorescens was studied as a model for dialysis fermentation. In a demonstration experiment, the continual removal of the product by dialysis and by intermittent replenishment of the dialysate reservoir caused cyclical changes in the concentrations of viable cells and product. The cumulative total amount of both cell mass and salicylate, however, continued to increase steadily until the experiment was terminated after 15 days. At this time the rate of product formation was highest and still increasing, although less than 10% of the cells were viable. The terminal amount of salicylate was about 20‐fold greater than the maximum reached in the control fermentation, and was calculated to be 2.6‐fold more productive even if the control were optimally recycled. Methods were projected to achieve still further improvements.
Degradation and mineralization of petroleum in sea water: Limitation by nitrogen and phosphorous
Authors: Atlas Ronald M. , Bartha Richard
Published: December 2004

Biodegradation and mineralization of petroleum, added at 1% (v/v) to freshly collected sea water, were measured using gas–liquid chromatographic, residual weight, and CO2‐evolution techniques. Only 3% of the added petroleum was biodegraded and 1% was mineralized in unamended sea water after 18 days of incubation. Added individually, nitrate (10−2 M) or phosphate (3.5 × 10−4 M) supplements caused little improvement, but when added in combination, they increased petroleum biodegradation and mineralization to 70% and 42%, respectively. Attempts to clean up oil spills with the aid of microorganisms should take into consideration the nutritional deficiencies of sea water.
Flocculant production from kerosene
Authors: Knettig E. , Zajic J. E.
Published: December 2004

Cultivation of Corynebacterium hydrocarboclastus, which is capable of synthesizing an extracellular polymer and utilized hydrocarbons, has been reported. Growth studies in shake flasks and fermenters were made to obtain maximum polymer production. Polymer formation was found to be growth associated. The highest level of polymer accumulation was attained after 50–60 hr cultivation in the fermenter and it amounted to approximately 5.5–6 g/liter of fermentation broth. The medium contained initially 2% (v/v) kerosene as a carbon source. The maximum yield obtained corresponds to 37–40% (w/w) of kerosene supplied. At the same time the cell concentration was 10–13 g/liter which represents the yield of 67–87% (w/w). The rate of polymer production in the exponential phase was 0.25 g/liter hr and cell production rate was 0.27 g/liter hr. Sodium nitrate, 0.5%, and yeast extract, 0.3%, (w/w) were the best nigrogen sources for polymer formation. The highest level of polymer produced in broth was 6 g/liter.
Thermal inactivation of immobilized enzymes in ideal continuous reactors
Authors: O'Neill S. P.
Published: December 2004

The limitation of thermal inactivation on catalytic activity in continuous enzymatic reactions is considered. Where an enzyme is retained in a reaction environment which is open to mass transfer of reaction components, the effect of enzyme inactivation on reactant conversion depends on the order of the chemical reaction and the pattern of fluid flow through the reaction volume. Equations expressing conversion as a function of time for first‐order inactivation are presented for Michaelis‐Menten kinetics and the limiting fluid flow conditions of plug flow and complete back‐mixing. Substrate protection or destruction of an enzyme is also considered and it is shown theoretically that the catalytic life of an enzyme may be optimized by the proper choice of fluid flow pattern.
Covalent coupling of pullulanase to an acrylic copolymer using a water soluble carbodi‐imide
Authors: Mårtensson Kaj , Mosbach Klaus
Published: December 2004

Pullulanase (EC 3.2.1.9) prepared from a culture of Acrobacter aerogeneshas been covalently bound to an inert crosslinked copolymer of aerylamide‐acrylic acid by using a water‐soluble carbodi‐imide. The binding yield based on the amount of added pullulanase was 34%. The residual enzymic activity was 43%, of that of free enzyme. Coupling in the presence of the substrate pullulan gave a 5‐fold increase in activity over that obtained when substrate was lacking. The effect of different carbodi‐imide concentrations on the coupling has been investigated. The isoelectric point of the pullulanase preparation (3.5–4.0) was determined using isoelectric, focusing, in order to find optimal pH conditions for the coupling procedure. The immobilized pullulanase in a packed bed column was used to debranch amylopeetin to low molecular weight amylose.
The fermentation of L‐sorbose by Gluconobacter melanogenus. II. Inducible formation of enzyme catalyzing conversion of L‐sorbose to 2‐keto‐L‐gulonic acid
Authors: Tsukada Y. , Perlman D.
Published: December 2004

Cell‐free extracts of Gluconobacter melanogenus cells grown in L‐sorbose‐containing media contained an enzyme system capable of converting L‐sorbose to 2‐keto‐L‐gulonic acid while cells grown in glycerol media did not. This inducible enzyme was located in the participate fraction of the cells.
Quantitative studies of the development of S. cerevisiae mitochondria
Authors: Ferdouse M. , Rickard Pamela A. D. , Moss F. J. , Blanch H. W.
Published: December 2004

The quantitative changes in mitochondria and cytochromes during transition of Saccharomyces cerevisiae from one steady state to another, while growing in continuous culture under controlled environmental conditions, were followed.

No Mitochondria, or mitochondria like structures, were detectable in electron micrographs of permanganate‐fixed anaerobic cells. Microaerobiosis (3μM dissolved oxygen) was sufficient to visualize mitochondrial profiles and induce cytochromes and their sections had a reduced number of mitochondrial profiles compared with cells grown in limiting glucose.

In the presence of ergosterol and Tween 80 mitochondriogenesis, whether induced by aerobiosis or glucose limitation, involved enhanced definition of crystal and outer mitochondrial membranes and increased number of profiles. Where membrane formation was limited, by the absence of aerobiosis involved eytochrome induction and profile visualization, but limited profile Proliferation; the adapted cells consequently contained fewer, but more eytochrome‐enriched, mitochondria than cells adapted in the presence of ergosterol and Tween 80.

Increase in dissolved oxygen from 3μM to 52μM further enhanced membrane definition and increased the size, but not the number, of mitochondrial profiles.

Evidence, obtained by measurement of eytochrome concentration per unit mitochondrial volume and per unit crystal area, support the concept that mitochondriogensis and cytochrome synthesis are not synchronized process and that cytochromes are added to or depleted from the mitochondrial cristae in response to culture conditions.
Binding of end product in the fermentation of nucleotides
Authors: Schwartz J. , Margalith P.
Published: December 2004

Flavor enhancing nucleotides may be produced by streptomycetes. Mutants of streptomyces 772 were found to produce, under ordinary fermentation conditions, considerable amounts of 5′‐IMP and 5′‐XMP, but only traces of 5′‐GMP. This was probably due to the feedback inhibition of the end product GMP. It was shown that through suitable fermentation techniques it was possible to overcome this internal control mechanism, leading to increased yields of 5′‐GMP.
Observations of continuous culture responses to additions of inhibitors
Authors: Borzani Walter , Vairo Marina L. R.
Published: December 2004

The effect of potassium sorbate addition to a continuous culture of Saccharomyces cerevisiae was observed. The influence on the yeast performance depended on the way the inhibitor was added. The unsteady state continuous method seems to be the best one to obtain microorganisms' adaptation to inhibitors, and for the experimental study of microbial inhibition.
The clarification of mechanically disrupted yeast suspensions by rotary vacuum precoat riltration
Authors: Gray P. P. , Dunnill P. , Lilly M. D.
Published: December 2004

Rotary vacuum precoat filtration of bakers' yeast disrupted in a high‐pressure homogenizer is reported. Different precoat materials, knife cutting rates, and body feeds were tested on disrupted yeast suspensions ranging from 10 to 40% wt packed yeast/vol. The flow rates, solids contents, and protein and enzyme concentrations before and after filtration were determined. Filtration rates were found to be independent of precoat thickness during debris filtration. For 20% disrupted yeast, flow rates of up to 17 cm3/cm2/hr were attained at a precoat and body feed usage of 35 kg/1000 liters. By reducing the knife cutting speed to 0.025 mm/min and the body feed to 1% the filter aid usage could be reduced to 13.5 kg/1000 liters while maintaining a flow rate of 9.3 cm3/cm2/hr. In all experiments protein recoveries were in the range of 80−90% and with the four enzymes examined, recoveries ranged from 67−92%. With all the precoats tested, the product had a lower solids content than that obtained from centrifuges capable of processing similar quantities of cell debris.
Response of completely mixed systems to pH shock
Authors: George T. K. , Gaudy A. F.
Published: December 2004

The response of aerobically growing heterogeneous microbial populations of sewage origin to step increases and decreases in pH were studied in both once‐through and cell recycle systems. The pH range studied was 2.7 to 8.0. All studies were conducted at a dilution rate of 0.125 hr−1, and all shocks were administered from a base or preshock pH level of 6.4 to 6.7. In each experiment, the preshock or initial “steady state” was assessed, the pH of the feed changed, and the resulting transient behavior of the system examined until attainment of the new or final “steady state” was approached. The major objectives of the work were to characterize the nature of the response with respect to biomass and effluent substrate concentrations, types of microbial populations present and chemical composition of the biomass, and to obtain guidelines as to allowable change in pH in waste streams. It was found in once‐through systems that substrate removal efficiency recovered from pH levels as low as 3.0 after rather long periods of transient leakage of substrate. Cell recycle attenuated the severity of substrate leakage. In all cases of severe acid shock, the microbial population changed from predominantly bacterial‐protozoan to one consisting predominantly of filamentous fungi. Changes in chemical composition of the sludge (protein and carbohydrate content) were consistent with the population changes. Based upon the results, it can be conservatively estimated that changes in pH of no more than one unit from the neutral preshock range can be tolerated without possible disruption of biochemical efficiency of substrate removal.
Studies on adsorption of amyloglucosidase on ion‐exchange resins
Authors: Solomon B. , Levin Y.
Published: December 2004

Highly charged water‐soluble conjugates of amyloglucosidase with a copolymer of ethylene‐maleic acid or styrene‐maleic acid were prepared and adsorbed on DEAE‐cellulose and other cationic resins. Negatively charged enzyme conjugates were also obtained by means of succinylation. The polyanionic conjugates of amyloglucosidase adsorbed on the cationic carriers show higher temperature stability than the native enzyme adsorbed on the same carriers under the same experimental conditions. The insoluble enzyme conjugate‐carrier complexes could be reused and retained their full activity while working continuously for three weeks. The application of the insoluble enzyme preparations with the above characteristics which could possibly satisfy the requirements for industry are discussed.
Immobilized enzymes: Pectin esterase covalently coupled to dorous glass particles
Authors: Weibel M. K. , Barrios Roberto , Delotto R. , Humphrey A. E.
Published: December 2004

Pectin esterase (E.C. 3.1.1.11) was covalently immobilized to porous glass particles by reaction of the native protein with pendant, benzoyl azide groups of the carrier. Enzyme loading on the carrier was 0.5 unit per ml as measured by pH stat, assay. Decreasing the size of the immobilized enzyme particles by grinding produced a 12‐fold increase in activity suggesting severe internal mass transport restrictions on turnover kinetics, Gross fractionation of the citrus pectin substrate into high and low molecular weight categories and their subsequent use in kinetic characterization shows no effect of molecular weight upon the kinetic behavior of the native enzyme. In contrast the immobilized enzyme displayed a 5‐fold increase in the apparent. Km for the high molecular weight fraction relative to that of the low molecular weight fraction. A striking difference exists in the low pH profile of immobilized pectin esterase relative to the native enzyme. Carrier matrix interactions with the polyelectrolyte substrate are invoked to explain this difference. The thermal stability of the immobilized enzyme is relatively low and displays a half‐life of approximately 2 weeks at 25°C.
Models for the continuous culture of microorganisms under both oxygen and carbon limiting conditions
Authors: Sinclair C. G. , Ryder D. N.
Published: December 2004

Two models for predicting the behavior of cultures of microorganisms under both oxygen and carbon limiting conditions have been evlauated on a chemostat growing Candida utilis on a glycolysis suppressing glycerol medium. The work indicated that parameter values obtained under wholly oxygen limiting or wholly carbon limiting conditions successfully predict the behavior of the chemostat under the wide range of flow and substrate concentration conditions tested. Both models are satisfactory and hence it is deduced that the simpler one may be used with confidence. It was found that Monod kinetics were applicable to the growth rate dependence on oxygen concentration but that Contois kinetics were superior for the corresponding dependence on carbon substrate concentration.
A kinetic model for microbial growth on liquid hydrocarbons
Authors: Chakravarty M. , Singh H. D. , Baruah J. N.
Published: December 2004

A kinetic model is presented to explain microbial growth using liquid n‐alkanes as substrate. The model is based on the assumption that growth occurs on the soluble alkane and that the metabolite produced by the growing cells helps the dissolution of liquid alkanes in the aqueous medium. Growth curves based on that model fit well with growth data for batch and continuous culture reported by various authors. The model also explains the differences between the relative length of exponential and linear phases of growth reported earlier.
Enzymatic preparation of 20β‐hydroxysteroids in a two‐phase system
Authors: Cremonesi Pietro , Carrea Giacomo , Ferrara Luigi , Antonini Eraldo
Published: December 2004

The behavior of 20β–hydroxysteroid dehydrogenase in a two–phase system consisting of an emulsion of water with an immiscible organic solvent was investigated. The effect of several organic solvents on the stability, activity, and kinetic profile of the enzyme was considered. The most suitable system for carrying out the enzymatic reactionproved to be water–butyl acetate.

The production of high quantities of 20β–hydroxysteroids in 100% yield using catalytic amount of cofactor was achieved by coupling the 20β–, hydroxysteroid dehydrogenase and the alcohol dehydrogenase–catalyzed reactions.
Microbial film fermenters: Their present and future applications
Authors: Atkinson B. , Knights A. J.
Published: December 2004

The productivity of growth associated fermentations is dependent upon the quantity of biomass contained in the fermenter (microbial hold‐up). In contrast, the performance characteristics of a fermenter are dominated by the form in which the microbial hold‐up occurs, i.e., whether as films, flocs, or a combination of both. Industrial fermentations using biological films include biological waste‐water treatment (trickling filter, rotating disc), the “quick” vinegar process, animal tissue culture, and bacterial leaching.

Atkinson and Davies (Trans. Inst. Chem. Eng., 50, 208 (1972)), proposed a completely mixed microbial film fermenter (CMMFF) based upon the fluidized bed principle, for application to continuous operation when using growth associated systems. The potential performance characteristics of this fermenter are reviewed and the construction of a laboratory scale unit capable ofaseptic operation is described (volume 9 liters, maximum throughput 15 liter/hr). The fermenter has been continuously used for periods up to 2500 hr without contamination when growing brewer's yeast (NCYC 1026 flocculating). The experimental performance characteristics have been interpreted with the aid of the theory for the CMMFF.

The knowledge and experience gained to date is used as a basis for speculation as to the future role of microbial film fermenters in the biochemical process industries.
Dynamics of liquid flow in an up‐flow reactor‐used for anaerobic treatment of wastewater
Authors: Heertjes P. M. , Van Der Meer R. R.
Published: December 2004

By means of stimulus‐response experiments with a Li+ tracer, a description of the fluid flow in a 30 m3 reactor, used for anaerobic treatment of wastewater, was derived. It appeared that of the three parts that could be distinguished in the reactor (the sludge bed. The sludge blanket, and the settler), the sludge bed could be described as a combination of two perfectly mixed regions with bypassing and return flows; the sludge blanket was perfectly mixed, while the fluid flow in the settler could be described as plug flow. From experiments performed under different conditions it was concluded that 60 m3 gas/day were sufficient to provide good mixing and also that the height of the sludge bed should be 2–3 m. From this last conclusion it follows, e.g., that scale‐up of the 30 m3 reactor should be done by increasing the cross section of the reactor while homogeneously distributing the influent over the bottom.
Production of microbial protein from tree bark by Phanerochaete chrysosporium
Authors: Daugulis A. J. , Bone Derek H.
Published: December 2004

Phanerochaete chrysosporium was grown in fermentors on NaOH‐extracted maple, pine, and cedar barks at the optimum substrate concentration of 1% (w/v). The yields (mg protein/liter) on maple, pine, and cedar were 1500, 1200, and 880, respectively, which are probably due to the different lignin contents of the barks. Lignin is not utilized. The productivities at 30°C obtained for pine (4.07 × 10−2 g protein/liter hr) and cedar (2.63 × 10−2 g protein/liter hr) barks were greater than for maple (2.63 × 10−2 g protein/liter hr). The substrate (bark) was the limiting component of the fermentation. Over the 26–38°C temperature range protein productivity increased by a factor of three (1.55 × 10−2 vs. 4.61 × 10−2 g protein/liter hr) for maple bark. Low agitation rates resulted in an overproduction of cellulase and reduced levels of microbial protein.
Effect of hydraulic regime on organic polymer uptake in the activated sludge process
Authors: Maxham John V. , Maier Walter J.
Published: December 2004

Mathematical models presented in a previous paper (Biotechnol. Bioeng., 20, 865 (1978)) describing unsteady‐state bacterial growth on organic polymers are modified to predict the holding time necessary to attain a given treatment level in a steady‐state activated sludge process. Various hydraulic regimes for the activated sludge aeration basin are assumed, and it shown that the hydraulic regime strongly influences the total holding time necessary to attain a given treatment objective. Maintaining the highest possible concentrations of bacteria, extracelluar enzyme, cleavable polymer bond, and utilizable oligomer in the aeration basin during the course of treatment yields the highest possible organic nutrient uptake. However, it is shown that aeration‐basin hydraulic regimes that maintain relatively high levels of bacteria and extracellular enzyme also maintain relatively low levels of polymer bond and utilizable oligomer and vice versa. Thus the efficacy of a particular aeration‐basin hydraulic regime depends on its ability to maintain at high levels those concentrations that most strongly influence the kinetics of enzymatic hydrolysis or utilizable oligomer uptake.
Modeling cell concentration in complex media
Authors: Alford J. S.
Published: December 2004

A model that continuously predicts the concentration of microorganisms in complex medium fermentations is suggested. The model uses carbon dioxide evolution as its primary input and assumes that respiration activity can be differentiated into growth‐related and maintenance‐related functions. This model can be programmed on computer‐coupled vessels and used to standardize on a physiological fermentation inoculum transfer time. The cell concentration estimate can also be used to calculate specific growth rate and can be combined with additional monitored information to calculate other important fermentation parameters such as specific oxygen uptake.
Laboratory‐scale production of acetoin plus diacetyl by Enterobacter cloacae ATCC 27613
Authors: Gupta K. G. , Yadav N. K. , Dhawan S.
Published: December 2004

Conditions for the laboratory‐scale production of acetoin plus diacetyl by Enterobacter Cloacae ATCC 27613 were studied. Thirty‐five g acetoin plus diacetyl/50 g sucrose were obtained when fermentation was carried out in 2. 5 liter medium containing 12.5 g peptone and 12. 5 g yeast extract, at pH 7.0, in a 5 liter conical flask on a shaker (240rpm) at 28–30°C for 48 hr. Recovery of pure diacetyl was 85% of the total plus diacetyl.
Influence of manufacturing variables on the characteristics and effectiveness of chitosan products. III. Coagulation of cheese whey solids
Authors: Wu A. C. M. , Bough W. A. , Holmes M. R. , Perkins B. E.
Published: December 2004

Ten chitosan products, prepared as described in part I of this study, were evaluated in jar tests that measured their effectiveness for coagulation of suspended solids and removing turbidity from cheese whey. A polynominal regression analysis was found to be useful for determining the optimal effectiveness of each chistosan preparation, and was expressed as the percent reduction on turbidity per unit concentration of chitosan added. The effectiveness of the chitosan products was found to be inversely related to their molecular‐weight values. This situation was different from the findings described in part II of this study, in which the filterability of activated sludge was tested. Enzymatic deproteination yielded chitosan products that performed better than those produced by alkali deproteination. Demineralized products were also more effective than those that had not been demineralized. The preparations deacetylated under a nitrogen atmosphere were more effective than those deacetylated in air, but this was shown to be true only for the first 5 min of deacetylation. When deacetylated for 15 min, no differences were noted. In this study, differences in performance between the various products were largely due to the differing dosages required to achieve the maximum reduction in turbidity of cheese whey, while the maximum responses achieved by the various products tested were about the same. A commercial product, which was less effective as a sludge coagulating agent in part II of this study, was more effective for cheese whey coagulation and turbidity removal than the majority of the experimental chitosan preparations tested.
Human interferon production with diploid fibroblast cells grown on microcarriers
Authors: Giard Donald J. , Loeb David H. , Thilly W. G. , Wang D. I. C. , Levine D. W.
Published: December 2004

A variety of diploid human fibroblast lines have been successfully grown to high densities (>106 cell/ml) on recently developed microcarriers. Interferon induction using poly I·poly C and a superinduction procedure resulted in yields greater than 10,000 units/ml with one cell line. A direct comparison of microcarrier cultures to roller bottle cultures showed equivalent interferon yields on a per cell basis and some apparent differences relating to optimum inducer concentrations and kinetics of interferon accumulation.
Kinetics and stability of immobilized chicken liver xanthine dehydrogenase
Authors: Tramper Johannes , Angelino Steven A. G. F. , Müller Franz , van der Plas Henk C.
Published: December 2004

Xanthine dehydrogenase (EC 1.2, 1.37) was isolated from chicken livers and immobilized by adsorption to a Sepharose derivative, prepared by reaction of n‐octy‐lamine with CNBr‐activated Sepharose 4B. Using a crude preparation of enzyme for immobilization it was observed that relatively more activity was adsorbed that protein, but the yield of immobilized activity increased as a purer enzyme preparation was used. As more activity and protein were bound, relatively less immobilized activity was recovered. This effect was probably due to blocking of active xanthine dehydrogenase by protein impurities. The kinetics of free and immobilized xanthine dehydrogenase were studied in the pH range 7.5–9.1. The Km and V values estimated for free xanthine dehydrogenase increase as the pH increases; the K'm and V values for the immobilized enzyme go through a minimum at pH 8.1. By varying the amount of enzyme activity bound per unit volume of gel, it was shown that K'm is larger than Km as result of substrate diffusion limitation in the pores of the support material. Both free and immobilized xanthine dehydrogenase showed substrate activation at low concentrations (up to 2μM xanthine). Immobilized xanthine dehydrogenase was more stable than the free enzyme during storage in the temperature range of 4−50°C. The operational stability of immobilized xanthine dehydrogenase at 30°C was two orders of magnitude smaller than the storage stability. t½ was 9 and 800 hr, respectively. The operational stability was, however, better than that of immobilized milk xanthine oxidase (t½ = 1 hr). In addition, the amount of product formed per unit initial activity in one half‐life, was higher for immobilized xanthine dehydrogenase than for immobilized xanthine oxidase. Unless immobilized milk xanthine oxidase can be considerable stabilized, immobilized chicken liver xanthine dehydrogenase is more promising for application in organic synthesis.
Data consistency, yield, maintenance, and hysteresis in batch cultures of Candida lipolytica cultured on n‐hexadecane
Authors: Ferrer Alexies , Erickson L. E.
Published: December 2004

Candida lipolytica was cultured batchwise using n‐hexadecane as the main carbon source. Biomass production, n‐hexadecane consumption, oxygen consumption, and carbon dioxide evolution were measured to follow the fermentation. The consistency of the measured data was examined using integrated and instantaneous available electron and carbon balances. Values of the “true” growth yield, ηmax, and maintenance coefficient, me were estimated using three different sets of data (biomass and n‐hexadecane, oxygen and biomass, and CO2 and biomass), and the results were compared with estimates obtained from literature data. Hysteresis patterns were observed in plots of specific rates of oxygen consumption and carbon dioxide evolution versus specific growth rate.
Saccharification of cellolulose by the cellulolytic enzyme system of Thermonospora sp. I. Stability of cellulolytic activities with respect to time, temperature, and pH
Authors: Hägerdal Bärbel , Ferchak John D. , Pye E. Kendall
Published: December 2004

The stabilities and optima with respect to temperature and pH of the β‐glucosidase, Avicelase, and carboxymethylcellulase (CMCase) activity of Thermomonospora sp., in the culture filtrate, culture whole broth, and filtrate after sonication of culture solids, are reported. The β‐glucosidase is cell associated and has an optimal activity at about pH 6.5 and 55°C. In the whole culture broth, it has a half‐life of about 8 hr at 55°C and less than 1 hr at 60°C, while the half‐life of the activity in the sonicated, cell‐free filtrate is less than 1 hr at 55°C. The Avicelase and CMCase activities occur in the extracellular culture fluid and have optima at about pH 7.0 and 5.9, and 65 and 70°C, respectively. The CMCase activity is stable over 24 hr at 60°C, but declines by 50% in the same period at 65°C. The Avicelase activity declines by 15% over 24 hr at 55°C, and by 50% at 60°C. The highest pH studied (pH 7.3) was the most destabilizing for all three activities. The thermostable characteristics of the cellulases from Themomonospora appear to make them suitable for commercial saccharification processes operating at elevated temperatures.
The monod equation: A revisit and a generalization to product inhibition situations
Authors: Levenspiel Octave
Published: December 2004

This paper shows how to treat the substrate‐limiting Monod equation in a straight forward manner for different types of fermentors (plug‐flow, batch, and mixed‐flow) using the general language of chemical reaction engineering. Straight‐line plots are developed for directly finding the kinetic constants of the equation, and an example using Monod's original data illustrates the procedure. The Monod equation is then generalized to account for the effects of both substrate and inhibitory toxic wastes. Finally, for pure product inhibition performance, expressions are derived for various reactor types, and correlation graphs are developed for finding the kinetic constants of the reaction. An example from the recent literature shows that this equation form fits the data extremely well.
Kinetics of biphasic growth of yeast in continuous and fed‐batch cultures
Authors: Toda K. , Yabe I. , Yamagata T.
Published: December 2004

The influence of dilution rate on the production of biomass, ethanol, and invertase in an aerobic culture of Saccharomyces carlsbergensis was studied in a glucose‐limited chemostat culture. A kinetic model was developed to analyze the biphasic growth of yeast on both the glucose remaining and the ethanol produced in the culture. The model assumes a double effect where glucose regulates the flux of glucose catabolism (respiration and aerobic fermentation) and the ethanol utilization in yeast cells. The model could successfully demonstrate the experimental results of a chemostat culture featuring the monotonic decrease of biomass concentration with an increase of dilution rate higher than 0.2 hr−1 as well as the maximum ethanol concentration at a particular dilution rate around 0.5 hr−1. Some supplementary data were collected from an ethanol‐limited aerobic chemostat culture and a glucose‐limited anaerobic chemostat culture to use in the model calculation. Some parametric constants of cell growth, ethanol production, and invertase formation were determined in batch cultures under aerobic and anaerobic states as summarized in a table in comparison with the chemostat data. Using the constants, a prediction of the optimal control of a glucose fed‐batch yeast culture was conducted in connection with an experiment for harvesting a high yield of yeast cells with high invertase activity.
Production of high‐fructose syrup by a heat‐fixed Lactobacillus sp.
Authors: Bhatia Mamta , Prabhu K. A.
Published: December 2004

A Lactobacillus sp. isolated from soil and capable of growing on xylose‐containing medium exhibited high glucose isomerase activity. The enzyme was thermostable, stable toward dialysis, and activated by heat treatment. It did not show the presence of xylose or ribose isomerase activities; the Km for glucose and xylose substrates were 0.48M and 0.513M, respectively. The heat treatment of ultrasonic crude extract gave insoluble fixed active glucose isomerase enzyme. The properties of free and immobilized enzyme in heat‐fixed whole cells differed in many respects. The optimum temperature for enzyme activity changed from 70 to 85°C, the optimum substrate concentration changed from 1.0M to 2.4M, and the optimum pH from 7.4 to 6.0. Co2+ and Mg2+ ions activated the enzyme when used singly, but in combination they inhibited the enzyme and Mn2+ had no effect on the enzyme. Free and immobilized enzymes, when used in the used in the conversions of corn and bagasse hydrolysates to fructose, gave 58, 25.6%, and 50, 27.6% conversions, respectively. Immobilized enzyme retained a significant activity for more than 30 hr and was able to operate at higher glucose concentrations showing less products inhibition effect as compared to free enzyme. In the batch process it was able to operate for about eight cycles.
Dynamics of commensalistic systems with self‐ and cross‐inhibition
Authors: Sheintuch M.
Published: December 2004

Up to three stable steady states are possible in a simple commensalistic system, taking place in an open‐loop mixed reactor when the growth rates of the two species are inhibited by the substrates they prey on (Self‐inhibition). Two stable states are possible in a system with noncompetitive inhibition of the species by the substrate they are not preying on (cross‐inhibition). A large number of steady states as well as oscillatory states are possible when both self‐ and cross‐inhibition are strong. Multiplicity of steady states is also possible in a reactor with biomas recirculation for these kinetics. Yet, the latter is more stable than the open‐loop reactor in the sense that the domain of steady‐state multiplicity is narrower. The stability of steady states and the dynamics of the systems for each of the investigated kinetics are summarized in a qualitative phase plane. The importance of the analysis for improving the selectively and yield of the system and for predicting the response of the system to changes in the operating conditions, is discussed.
Immobilization of proteins by reductive alkylation with hydrophobic aldehydes
Authors: Wu Hua‐Lin , Means Gary E.
Published: December 2004

A new method is described for the immobilization of enzymes and other proteins onto hydrophobic gels. Trypsin, for example, can be quantitatively immobilized by reaction with sodium cyanoborohydride and dodecyladehyde‐coated Octyl‐Sepharose. Noncovalent interactions between the hydrophobic gel and approximately 10 resulting dodecylamino groups in the modified enzyme bind it very strongly but do not affect its ability to hydrolyze benzolarginine ethyl ester. The same procedure can also be used to immobilize E. Coli asparaginase and yeast alcohol dehydrogenase in high yield.
Multilevel control of multistage continuous culture using a microprocessor
Authors: Fawzy A. S. , Hinton O. R.
Published: December 2004

This paper describes the implementation of multilevel techniques using a microprocessor to control multistage continuous culture systems. A system which produces gramicidin S is taken as an example. The single level technique using the conjugate gradient method is applied to solve the two‐stage and the three‐stage continuous culture and is compared with the multilevel one. The results show that the application of multilevel techniques is more advantageous and suitable for this system than any other method which has been utilized so far. The advantages of using a microprocessor will be stated.
Fermentation pattern of sucrose to ethanol conversions by Zymomonas mobilis
Authors: Lyness Ed , Doelle Horst W.
Published: December 2004

General patterns of sucrose fermentation by two strains of Zymomonas mobilis, designated Z7 and Z10, were established using sucrose concentrations from 50 to 200 g/liter. Strain Z7 showed a higher invertase activity than Z10. Strain Z10 showed a reduced specific growth rate at high sucrose concentration while Z7 was unaffected. High sucrose hydrolyzing activity in strain Z7 lead to glucose accumulation in the medium at high sucrose concentrations. Ethanol production and fermentation time depend on the rate of catabolism of the products of sucrose hydrolysis, glucose and fructose. The metabolic quotients for sucrose utilization, qs, and ethanol production, qp (g/g·hr), are unsuitable for describing sucrose utilization by Zymomonas mobilis, as the logarithmic phase of growth precedes the phase of highest substrate utilization (g/liter·hr) and ethanol production (g/liter·hr) in batch culture.