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Specific Rates (specific + rate)
Selected AbstractsCalculation of the Specific Rate of Catabolic Activity (Ac) from the Heat Flow Rate of Soil Microbial Reactions Measured by Calorimetry: Significance and ApplicationsCHEMISTRY & BIODIVERSITY, Issue 10 2004Nieves Barros The calculation of parameters involved in the kinetics of the microbial soil reactions linked to the carbon cycle is strongly limited by the methodologies employed. Hence, a mathematical model is proposed to quantify easily the specific rate of catabolic activity Ac by microcalorimetry based on Belaich's model. It permits to quantify Ac from the plots of the heat flow rate vs. time recorded from soil samples amended with glucose. It was applied for several soil samples collected in the Amazon. The results obtained were compared, and statistical and graphical analyses were used to provide the biophysical significance of Ac in soils. Results suggest that Ac could be used as an empirical measure of stress. It correlates positively with the heat yield, YQ/X, of the soil microbial growth reactions, indicating that higher specific rates of catabolic activity cause higher dissipation of energy per unit of cell, yielding less-efficient metabolic reactions, which could affect negatively the soil quality. It is strongly affected by the initial microbial population and by the percentage of nitrogen in the samples. The statistical analysis also demonstrated that Ac is more sensitive to changing environmental conditions than YQ/X, yielding more-accurate information about the soil metabolic processes. [source] Dissimilatory ferrous iron oxidation at a low pH: a novel trait identified in the bacterial subclass RubrobacteridaeFEMS MICROBIOLOGY LETTERS, Issue 2 2008Christopher G. Bryan Abstract A novel iron-oxidizing acidophilic actinobacterium was isolated from spoil material at an abandoned copper mine. Phylogenetic analysis placed the isolate within the Rubrobacteridae subclass of the Actinobacteria. Its optimum temperature and pH for growth are 30,35 °C and pH 3.0, respectively. Although it could catalyze the dissimilatory oxidation of ferrous iron, growth yields declined progressively in media containing ferrous iron concentrations >100 ,M. The isolate, Pa33, did not grow or oxidize iron in the absence of organic carbon, and appeared to be an obligate heterotroph. Specific rates of iron oxidation were much smaller than those determined for the autotrophic iron-oxidizing proteobacterium Acidithiobacillus ferrooxidans and the heterotrophic iron-oxidizing actinobacterium Ferrimicrobium acidiphilum. Iron oxidation by isolate Pa33 appears to be a defensive mechanism, in which iron oxidation converts a soluble species to which the bacterium is sensitive to an oxidized species (ferric iron) that is highly insoluble in the spoil from which it was isolated. This is the first report of acidophily or dissimilatory iron oxidation within the Rubrobacteridae subclass and one of very few within the Actinobacteria phylum as a whole. [source] Heteroatoms and substituent effects: The importance of heteroatom hyperconjugationHETEROATOM CHEMISTRY, Issue 5 2002James F. King We have found that the specific rate of ,-sulfonyl carbanion formation in a ,-substituted sulfone shows a sizable dependence on the HC,C,X torsion angle. Defining kN = (kexch)X/(kexch)model (where the model has X = H or an alkyl group) we observed for a collection of ,-alkoxy sulfones (X = OR) acceptable agreement with the expression log kN = a + b cos2 , (where a = 1.70 and b = 2.62). Extension to other ,-substituents (X = RS, R2N, and R3N+) yields the same pattern, with the last showing very large dependence of kN on the torsion angle (b = 6.3). These observations are ascribed to the presence (in addition to the inductive and field effects) of negative hyperconjugation responsible for accelerations of 1000-fold and more, deriving from donation of the incipient negative charge on carbon into the ,*CX orbital in the transition state. These observations reflect, and at the same time underline, the importance of the low-lying antibonding orbitals present in heteroatomic molecules. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:397,405, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10067 [source] Genome-derived minimal metabolic models for Escherichia coli MG1655 with estimated in vivo respiratory ATP stoichiometryBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2010Hilal Taymaz-Nikerel Abstract Metabolic network models describing growth of Escherichia coli on glucose, glycerol and acetate were derived from a genome scale model of E. coli. One of the uncertainties in the metabolic networks is the exact stoichiometry of energy generating and consuming processes. Accurate estimation of biomass and product yields requires correct information on the ATP stoichiometry. The unknown ATP stoichiometry parameters of the constructed E. coli network were estimated from experimental data of eight different aerobic chemostat experiments carried out with E. coli MG1655, grown at different dilution rates (0.025, 0.05, 0.1, and 0.3,h,1) and on different carbon substrates (glucose, glycerol, and acetate). Proper estimation of the ATP stoichiometry requires proper information on the biomass composition of the organism as well as accurate assessment of net conversion rates under well-defined conditions. For this purpose a growth rate dependent biomass composition was derived, based on measurements and literature data. After incorporation of the growth rate dependent biomass composition in a metabolic network model, an effective P/O ratio of 1.49,±,0.26,mol of ATP/mol of O, KX (growth dependent maintenance) of 0.46,±,0.27,mol of ATP/C-mol of biomass and mATP (growth independent maintenance) of 0.075,±,0.015,mol of ATP/C-mol of biomass/h were estimated using a newly developed Comprehensive Data Reconciliation (CDR) method, assuming that the three energetic parameters were independent of the growth rate and the used substrate. The resulting metabolic network model only requires the specific rate of growth, µ, as an input in order to accurately predict all other fluxes and yields. Biotechnol. Bioeng. 2010;107: 369,381. © 2010 Wiley Periodicals, Inc. [source] Dynamic gene expression regulation model for growth and penicillin production in Penicillium chrysogenumBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2010Rutger D. Douma Abstract As is often the case for microbial product formation, the penicillin production rate of Penicillium chrysogenum has been observed to be a function of the growth rate of the organism. The relation between the biomass specific rate of penicillin formation (qp) and growth rate (µ) has been measured under steady state conditions in carbon limited chemostats resulting in a steady state qp(µ) relation. Direct application of such a relation to predict the rate of product formation during dynamic conditions, as they occur, for example, in fed-batch experiments, leads to errors in the prediction, because qp is not an instantaneous function of the growth rate but rather lags behind because of adaptational and regulatory processes. In this paper a dynamic gene regulation model is presented, in which the specific rate of penicillin production is assumed to be a linear function of the amount of a rate-limiting enzyme in the penicillin production pathway. Enzyme activity assays were performed and strongly indicated that isopenicillin-N synthase (IPNS) was the main rate-limiting enzyme for penicillin-G biosynthesis in our strain. The developed gene regulation model predicts the expression of this rate limiting enzyme based on glucose repression, fast decay of the mRNA encoding for the enzyme as well as the decay of the enzyme itself. The gene regulation model was combined with a stoichiometric model and appeared to accurately describe the biomass and penicillin concentrations for both chemostat steady-state as well as the dynamics during chemostat start-up and fed-batch cultivation. Biotechnol. Bioeng. 2010;106: 608,618. © 2010 Wiley Periodicals, Inc. [source] Using the rate of respiration to monitor events in the infection of Escherichia coli cultures by bacteriophage T4BIOTECHNOLOGY PROGRESS, Issue 3 2010Dominic Sauvageau Abstract The growing interest in applications of bacteriophages creates a need for improvements in the production processes. Continuous monitoring of the phage production is an essential aspect of any control strategy and, at present, there is no completely satisfactory option. The approach presented here uses IR-spectrometry to continuously measure the rate of respiration (CO2 released) of Escherichia coli infected by phage T4 at various multiplicities of infection (MOI). Within the trends in these data, or in other aspects of the rate of respiration, it was possible to reliably and reproducibly identify five features that reflected specific events in the infection process. These included two events in the host cell apparent growth rate and events in the magnitude of the host cell density, in the measurement of OD600 or in the specific rate of respiration. All of these correlations were within 95% confidence showing that they are suitable for the monitoring and control of E. coli populations infected by phage T4. This method is reliable, cheap, and can be operated in-line and in real time. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Error propagation from prime variables into specific rates and metabolic fluxes for mammalian cells in perfusion cultureBIOTECHNOLOGY PROGRESS, Issue 4 2009Chetan T. Goudar Abstract Error propagation from prime variables into specific rates and metabolic fluxes was quantified for high-concentration CHO cell perfusion cultivation. Prime variable errors were first determined from repeated measurements and ranged from 4.8 to 12.2%. Errors in nutrient uptake and metabolite/product formation rates for 5,15% error in prime variables ranged from 8,22%. The specific growth rate, however, was characterized by higher uncertainty as 15% errors in the bioreactor and harvest cell concentration resulted in 37.8% error. Metabolic fluxes were estimated for 12 experimental conditions, each of 10 day duration, during 120-day perfusion cultivation and were used to determine error propagation from specific rates into metabolic fluxes. Errors of the greater metabolic fluxes (those related to glycolysis, lactate production, TCA cycle and oxidative phosphorylation) were similar in magnitude to those of the related greater specific rates (glucose, lactate, oxygen and CO2 rates) and were insensitive to errors of the lesser specific rates (amino acid catabolism and biosynthesis rates). Errors of the lesser metabolic fluxes (those related to amino acid metabolism), however, were extremely sensitive to errors of the greater specific rates to the extent that they were no longer representative of cellular metabolism and were much less affected by errors in the lesser specific rates. We show that the relationship between specific rate and metabolic flux error could be accurately described by normalized sensitivity coefficients, which were readily calculated once metabolic fluxes were estimated. Their ease of calculation, along with their ability to accurately describe the specific rate-metabolic flux error relationship, makes them a necessary component of metabolic flux analysis. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Oxidant-Free Dehydrogenation of Alcohols Heterogeneously Catalyzed by Cooperation of Silver Clusters and Acid,Base Sites on AluminaCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2009Ken-ichi Shimizu Dr. Abstract Trifunctional green catalysis: In-depth characterization shows that oxidant-free selective oxidation of alcohols by silver nanoparticles on ,-Al2O3, as a new heterogeneous catalyst, proceeds through cooperation of silver, acid, and base sites (see figure). A ,-alumina-supported silver cluster catalyst,Ag/Al2O3,has been shown to act as an efficient heterogeneous catalyst for oxidant-free alcohol dehydrogenation to carbonyl compounds at 373,K. The catalyst shows higher activity than conventional heterogeneous catalysts based on platinum group metals (PGMs) and can be recycled. A systematic study on the influence of the particle size and oxidation state of silver species, combined with characterization by Ag,K-edge XAFS (X-ray absorption fine structure) has established that silver clusters of sizes below 1,nm are responsible for the higher specific rate. The reaction mechanism has been investigated by kinetic studies (Hammett correlation, kinetic isotope effect) and by in situ FTIR (kinetic isotope effect for hydride elimination reaction from surface alkoxide species), and the following mechanism is proposed: 1),reaction between the alcohol and a basic OH group on the alumina to yield alkoxide on alumina and an adsorbed water molecule, 2),CH activation of the alkoxide species by the silver cluster to form a silver hydride species and a carbonyl compound, and 3),H2 desorption promoted by an acid site in the alumina. The proposed mechanism provides fundamental reasons for the higher activities of silver clusters on acid,base bifunctional support (Al2O3) than on basic (MgO and CeO2) and acidic to neutral (SiO2) ones. This example demonstrates that catalysts analogous to those based on of platinum group metals can be designed with use of a less expensive d10 element,silver,through optimization of metal particle size and the acid,base natures of inorganic supports. [source] Calculation of the Specific Rate of Catabolic Activity (Ac) from the Heat Flow Rate of Soil Microbial Reactions Measured by Calorimetry: Significance and ApplicationsCHEMISTRY & BIODIVERSITY, Issue 10 2004Nieves Barros The calculation of parameters involved in the kinetics of the microbial soil reactions linked to the carbon cycle is strongly limited by the methodologies employed. Hence, a mathematical model is proposed to quantify easily the specific rate of catabolic activity Ac by microcalorimetry based on Belaich's model. It permits to quantify Ac from the plots of the heat flow rate vs. time recorded from soil samples amended with glucose. It was applied for several soil samples collected in the Amazon. The results obtained were compared, and statistical and graphical analyses were used to provide the biophysical significance of Ac in soils. Results suggest that Ac could be used as an empirical measure of stress. It correlates positively with the heat yield, YQ/X, of the soil microbial growth reactions, indicating that higher specific rates of catabolic activity cause higher dissipation of energy per unit of cell, yielding less-efficient metabolic reactions, which could affect negatively the soil quality. It is strongly affected by the initial microbial population and by the percentage of nitrogen in the samples. The statistical analysis also demonstrated that Ac is more sensitive to changing environmental conditions than YQ/X, yielding more-accurate information about the soil metabolic processes. [source] Oxygen transfer effects in ,-lactamase fermentation by Bacillus licheniformis in a glucose-based defined mediumJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2005nar Çal Abstract The effects of oxygen transfer on the ,-lactamase production by Bacillus licheniformis were investigated in a glucose-based defined medium. The experiments were conducted in 3.0 dm3 batch bioreactor systems at three different air inlet (QO/VR = 0.2, 0.5 and 1.0 vvm) and agitation rates (N = 250, 500 and 750 min,1). During the fermentation, the concentrations of the cell, glucose, by-products, ie organic and amino acids, oxygen transfer coefficients (KLa), yield coefficients, specific rates and oxygen uptake rates (OUR) were determined, in addition to ,-lactamase activities. The highest ,-lactamase activity was obtained at QO/VR = 0.5 vvm and N = 500 min,1 and at QO/VR = 0.2 vvm and N = 500 min,1 conditions, as caA = 90 U cm,3. The highest cell concentration was obtained as CX = 0.67 kg m,3 at QO/VR = 0.5 vvm and N = 750 min,1 and at QO/VR = 0.2 vvm and N = 750 min,1 conditions. The values of KLa increased with increasing agitation and aeration rates and varied between 0.007 and 0.044 s,1, and the OUR varied between 0.4 and 1.6 mol m,3 s,1. With increasing QO/VR and/or N, the Damköhler number (ie the oxygen transfer limitation) decreased owing to the increase in mass transfer coefficients (KLa). The highest instantaneous yield of cell on substrate (YX/S) and yield of cell on oxygen (YX/O) values were respectively obtained at 0.5 vvm and 500 min,1 conditions at t = 2 h as YX/S = 0.72 kg kg,1 and YX/O = 1.49 kg kg,1. The highest instantaneous yield of substrate on oxygen (YS/O) was obtained at 0.5 vvm and 750 min,1 conditions at t = 20 h as YS/O = 8.07 kg kg,1. Copyright © 2005 Society of Chemical Industry [source] The fermentation of mixtures of D -glucose and D -xylose by Candida shehatae, Pichia stipitis or Pachysolen tannophilus to produce ethanolJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2002Sebastián Sánchez Abstract The fermentation of mixtures of D -glucose and D -xylose by three non-traditional yeasts: Candida shehatae (ATCC 34887), Pachysolen tannophilus (ATCC 32691) and Pichia stipitis (ATCC 58376) have been studied to determine the optimal strain and initial culture conditions for the efficient production of ethanol. The comparison was made on the basis of maximum specific growth rate (µm), biomass productivity, the specific rates of total substrate consumption (qs) and ethanol production (qE) and the overall yields of ethanol and xylitol. All the experiments were performed in stirred-tank batch reactors at a temperature of 30,°C. The initial pH of the culture medium was 4.5. The highest values of µm (above 0.5,h,1) were obtained with P stipitis in cultures containing high concentrations of D -xylose. All three yeasts consumed the two monosaccharides in sequence, beginning with D -glucose. The values of qs diminished during the course of each experiment with all of the yeasts. The highest values of the specific rates of total substrate consumption and ethanol production were obtained with C shehatae (for t,=,10,h, qs and qE were above 5,g,g,1,h,1 and 2,g,g,1,h,1, respectively), although the highest overall ethanol yields were fairly similar with all three yeasts, at around 0.4,g,g,1. © 2002 Society of Chemical Industry [source] Rate and product studies in the solvolyses of methanesulfonic anhydride and a comparison with methanesulfonyl chloride solvolyses,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2007Dennis N. Kevill Abstract The specific rates of solvolysis of methanesulfonic anhydride have been measured conductometrically at ,10,°C in 41 solvents. Use of the extended Grunwald,Winstein equation, with the NT scale of solvent nucleophilicity and the YOTs scale of solvent ionizing power, leads to sensitivity to changes in solvent nucleophilicity (, value) of 0.95 and a sensitivity to changes in solvent ionizing power (m value) of 0.61, with a multiple correlation coefficient (R) of 0.973. Product selectivity values (S) in binary hydroxylic solvents favor alcohol attack in EtOH,H2O (a value of 1.2 in 90% EtOH rising to 4.0 in 40% EtOH) and in MeOH,H2O (a value of 3.7 in 90% MeOH rising to 6.0 in 50% MeOH). In 2,2,2,-trifluoroethanol,H2O, the S values are much lower at about 0.1. Entropy of activation values are appreciably negative. Literature values for the specific rates of solvolysis of methanesulfonyl chloride have been extended to fluoroalcohol-containing solvents (titrimetric method) and, at 45.0,°C, for an overall 43 solvents values are obtained (using NT and YC1 scales) of 1.20 for , and of 0.52 for m (R,=,0.969). It is proposed that both substrates solvolyze by an SN2 pathway. Copyright © 2007 John Wiley & Sons, Ltd. [source] Correlation of the rates of solvolysis of benzoyl chloride and derivatives using extended forms of the Grunwald,Winstein equation,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2002Dennis N. Kevill Abstract Available specific rates of solvolysis at 25,°C of benzoyl chloride and four para -substituted derivatives for which both NT and YCl values are tabulated were analyzed using the extended (two-term) Grunwald,Winstein equation. The ionization pathway with appreciable nucleophilic solvation of the incipient carbocation observed for the p -methoxy derivative is accompanied by increasingly important regions of dominant operation of an addition,elimination pathway as the Hammett , value for the substituent increases. Accordingly, for the p -nitro derivative only the 97% HFIP data point deviates from the addition,elimination correlation. Correlations of the specific rates of solvolysis of 2,6-dimethylbenzoyl chloride are improved by incorporation of a term governed by the aromatic ring parameter (I). Copyright © 2002 John Wiley & Sons, Ltd. [source] Alcohol consumption patterns and predictors of use following liver transplantation for alcoholic liver diseaseLIVER TRANSPLANTATION, Issue 5 2006Andrea DiMartini For patients who receive a liver transplant (LTX) for alcoholic liver disease (ALD), investigators are focusing beyond survival to determine specific alcohol use outcomes. Studies suggest the use of alcohol ranges from 8 to 22% for the first post-transplant year with cumulative rates reaching 30 to 40% by 5 years following transplantation. Yet while investigators are interested in determining specific rates of alcohol use and predictors of use, only three studies since 1990 have been prospective. In 1998, we began a prospective study of post-LTX alcohol consumption in ALD recipients using multiple repeated measures of alcohol use. After 5 years of follow-up, we found that 22% had used any alcohol by the first year and 42% had a drink by 5 years. By 5 years, 26% drank at a heavier use (binge) pattern and 20% drank in a frequent pattern. In a univariate model, predictors of alcohol use included pre-transplant length of sobriety, a diagnosis of alcohol dependence, a history of other substance use, and prior alcohol rehabilitation. Liver Transpl 12:813,820, 2006. © 2006 AASLD. [source] External cause-specific summaries of occupational fatal injuries.AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 3 2003Part I: An analysis of rates Abstract Background Industries and occupations vary with respect to the incidence of fatal injuries and their causes. Methods Fatalities from the National Traumatic Occupational Fatality database (years 1983,1994) serve as the basis for examining external cause of death code specific rates. Industries and occupations are compared with respect to rate and frequency of fatal injuries. In addition, external causes of injury (E-codes) are examined across all industries and occupations as well as within industries and occupations to evaluate which events would be identified by frequency ordered comparisons versus injury rate ordered comparisons. Results Machinery, electric current, homicide, falls, and transportation-related events are identified by high frequency and rate of occurrence. Conclusions The external cause categories of homicide, machinery-related, motor-vehicle-related, electric current, and falls, account for over one-half of all occupational fatal injuries. Targeted interventions in homicide may be especially warranted in sales and service occupations and in the retail trade and services industries. In addition, younger workers might be targeted for special interventions designed to identify hazardous practices, procedures, and solutions to reduce fatalities associated with electrocution or falls from buildings. Am. J. Ind. Med. 43:237,250, 2003. Published 2003 Wiley-Liss, Inc. [source] Hydrogen photoproduction by nutrient-deprived Chlamydomonas reinhardtii cells immobilized within thin alginate films under aerobic and anaerobic conditionsBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009Sergey N. Kosourov Abstract A new technique for immobilizing H2 -photoproducing green algae within a thin (<400 µm) alginate film has been developed. Alginate films with entrapped sulfur/phosphorus-deprived Chlamydomonas reinhardtii, strain cc124, cells demonstrate (a) higher cell density (up to 2,000 µg Chl mL,1 of matrix), (b) kinetics of H2 photoproduction similar to sulfur-deprived suspension cultures, (c) higher specific rates (up to 12.5 µmol,mg,1,Chl,h,1) of H2 evolution, (d) light conversion efficiencies to H2 of over 1% and (e) unexpectedly high resistance of the H2 -photoproducing system to inactivation by atmospheric O2. The algal cells, entrapped in alginate and then placed in vials containing 21% O2 in the headspace, evolved up to 67% of the H2 gas produced under anaerobic conditions. The results indicate that the lower susceptibility of the immobilized algal H2 -producing system to inactivation by O2 depends on two factors: (a) the presence of acetate in the medium, which supports higher rates of respiration and (b) the capability of the alginate polymer itself to effectively separate the entrapped cells from O2 in the liquid and headspace and restrict O2 diffusion into the matrix. The strategy presented for immobilizing algal cells within thin polymeric matrices shows the potential for scale-up and possible future applications. Biotechnol. Bioeng. 2008. Biotechnol. Bioeng. 2009;102: 50,58. © 2008 Wiley Periodicals, Inc. [source] Error propagation from prime variables into specific rates and metabolic fluxes for mammalian cells in perfusion cultureBIOTECHNOLOGY PROGRESS, Issue 4 2009Chetan T. Goudar Abstract Error propagation from prime variables into specific rates and metabolic fluxes was quantified for high-concentration CHO cell perfusion cultivation. Prime variable errors were first determined from repeated measurements and ranged from 4.8 to 12.2%. Errors in nutrient uptake and metabolite/product formation rates for 5,15% error in prime variables ranged from 8,22%. The specific growth rate, however, was characterized by higher uncertainty as 15% errors in the bioreactor and harvest cell concentration resulted in 37.8% error. Metabolic fluxes were estimated for 12 experimental conditions, each of 10 day duration, during 120-day perfusion cultivation and were used to determine error propagation from specific rates into metabolic fluxes. Errors of the greater metabolic fluxes (those related to glycolysis, lactate production, TCA cycle and oxidative phosphorylation) were similar in magnitude to those of the related greater specific rates (glucose, lactate, oxygen and CO2 rates) and were insensitive to errors of the lesser specific rates (amino acid catabolism and biosynthesis rates). Errors of the lesser metabolic fluxes (those related to amino acid metabolism), however, were extremely sensitive to errors of the greater specific rates to the extent that they were no longer representative of cellular metabolism and were much less affected by errors in the lesser specific rates. We show that the relationship between specific rate and metabolic flux error could be accurately described by normalized sensitivity coefficients, which were readily calculated once metabolic fluxes were estimated. Their ease of calculation, along with their ability to accurately describe the specific rate-metabolic flux error relationship, makes them a necessary component of metabolic flux analysis. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Development of a Transient Segregated Mathematical Model of the Semicontinuous Microbial Production Process of DihydroxyacetoneBIOTECHNOLOGY PROGRESS, Issue 1 2006Rüdiger Bauer For the mathematical description of the semicontinuous two-stage repeated-fed-batch fermentation of dihydroxyacetone (DHA), a novel segregated model incorporating transient growth rates was developed. The fermentation process was carried out in two stages. A viable, not irreversibly product-inhibited culture was maintained in the first reactor stage until a predetermined DHA threshold value was reached. In the second reactor stage, high final product concentrations of up to 220 g L,1 were reached while the culture was irreversibly product-inhibited. The experimentally observed changes of the physiological state of the culture due to product inhibition were taken into account by introducing a segregation into the mathematical model. It was shown that the state of the cells was dependent on the current environment and on the previous history. This phenomenon was considered in the model by utilizing delay time equations for the specific rates of growth on the primary and the secondary substrate. A comparison with reproducible measurements gave a good correlation between computation and experiment. The mathematical model was validated using independent own experimental data. A comparison with a stationary and nonsegregated model demonstrated the essential improvements of the novel model. It was deduced from the model calculations that high product formation rates of 3.3,3.5 g L,1 h,1 as well as high final DHA concentrations of 196,215 g L,1 can be obtained with a residual broth volume in the first reactor stage of 2% and a DHA threshold value in the range of 100,110g L,1. [source] Logistic Equations Effectively Model Mammalian Cell Batch and Fed-Batch Kinetics by Logically Constraining the FitBIOTECHNOLOGY PROGRESS, Issue 4 2005Chetan T. Goudar A four-parameter logistic equation was used to fit batch and fed-batch time profiles of viable cell density in order to estimate net growth rates from the inoculation through the cell death phase. Reduced three-parameter forms were used for nutrient uptake and metabolite/product formation rate calculations. These logistic equations constrained the fits to expected general concentration trends, either increasing followed by decreasing (four-parameter) or monotonic (three-parameter). The applicability of this approach was first verified for Chinese hamster ovary (CHO) cells cultivated in 15-L batch bioreactors. Cell density, metabolite, and nutrient concentrations were monitored over time and used to estimate the logistic parameters by nonlinear least squares. The logistic models fit the experimental data well, supporting the validity of this approach. Further evidence to this effect was obtained by applying the technique to three previously published batch studies for baby hamster kidney (BHK) and hybridoma cells in bioreactors ranging from 100 mL to 300 L. In 27 of the 30 batch data sets examined, the logistic models provided a statistically superior description of the experimental data than polynomial fitting. Two fed-batch experiments with hybridoma and CHO cells in benchtop bioreactors were also examined, and the logistic fits provided good representations of the experimental data in all 25 data sets. From a computational standpoint, this approach was simpler than classical approaches involving Monod-type kinetics. Since the logistic equations were analytically differentiable, specific rates could be readily estimated. Overall, the advantages of the logistic modeling approach should make it an attractive option for effectively estimating specific rates from batch and fed-batch cultures. [source] Calculation of the Specific Rate of Catabolic Activity (Ac) from the Heat Flow Rate of Soil Microbial Reactions Measured by Calorimetry: Significance and ApplicationsCHEMISTRY & BIODIVERSITY, Issue 10 2004Nieves Barros The calculation of parameters involved in the kinetics of the microbial soil reactions linked to the carbon cycle is strongly limited by the methodologies employed. Hence, a mathematical model is proposed to quantify easily the specific rate of catabolic activity Ac by microcalorimetry based on Belaich's model. It permits to quantify Ac from the plots of the heat flow rate vs. time recorded from soil samples amended with glucose. It was applied for several soil samples collected in the Amazon. The results obtained were compared, and statistical and graphical analyses were used to provide the biophysical significance of Ac in soils. Results suggest that Ac could be used as an empirical measure of stress. It correlates positively with the heat yield, YQ/X, of the soil microbial growth reactions, indicating that higher specific rates of catabolic activity cause higher dissipation of energy per unit of cell, yielding less-efficient metabolic reactions, which could affect negatively the soil quality. It is strongly affected by the initial microbial population and by the percentage of nitrogen in the samples. The statistical analysis also demonstrated that Ac is more sensitive to changing environmental conditions than YQ/X, yielding more-accurate information about the soil metabolic processes. [source] | ||||||||||||||||