An unstructured model for the analysis of substrate consumption and product release in relation to biosynthesis and cell maintenance during batch cultures of Geotrichum candidum and Penicillium camembertii

An unstructured model has been developed to predict microbial growth based on carbon or nitrogen substrate consumption, ammonia or carbon dioxide production and proton transfer. The model has been validated for batch cultures of Geotrichum candidum and Penicillium camembertii growing on peptones and peptones + lactate based media. The contributions of the considered kinetics to biosynthesis and cellular maintenance can be deduced from this model. The nitrogen source (peptones) was mainly utilized in biosynthesis: for P camembertii growing on peptones, 86% of the metabolized peptones. G candidum metabolized peptones preferentially to lactate as a carbon source, resulting in lactate utilization by a maintenance mechanism during the stationary state. In contrast, P camembertii, which metabolized fewer amino acids as a carbon source, utilized lactate mainly for biosynthesis (83% of the consumed lactate). Most (up to 71%) of the ammonia released was produced by deamination of amino acids utilized as both carbon and nitrogen sources by growth‐associated metabolism. With peptones, proton transfer resulted from ammonia release, most likely as a result of the growth‐associated mechanism, as supported experimentally (55–58% of the released ammonia for both microorganisms). The contribution of lactate to proton transfer resulted in 76% of protons exchanged by a growth‐associated mechanism during P camembertii growth. For total carbon dioxide production, the contributions of the energy supplies for biosynthesis and cell maintenance were similar; except during P camembertii growth in the presence of lactate (65% of growth‐associated CO₂ production). © 2002 Society of Chemical Industry     

Amino acids as carbon,energy and nitrogen sources for Penicillium camembertii

Three groups of amino acids were previously characterized on their ability to be assimilated as carbon source by Penicillium camembertii. In view of a deeper understanding of their metabolic behaviour, growth of P. camembertii on glucose, the limiting substrate, and an amino acid was examined in batch culture. Amino acids from the first group (Cys, His, Lys, Met, Trp and Val) are convenient nitrogen sources, but cannot be assimilated as carbon sources. However, they are also dissimilated, namely used for energy supply by oxidation into CO₂, during stationary phase, after glucose depletion, as shown for lysine; and the corresponding nitrogen was released as ammonium. Growth exhibited diauxic behaviour for the second group of amino acids (Arg, Leu), since they can be assimilated as carbon sources, in addition to their assimilation as nitrogen sources, but only after glucose depletion, as shown for arginine. A clear differentiation between the assimilated and the dissimilated carbon was demonstrated for the third group of amino acids (Ala, Asp, Glu, Gly, Pro, Ser, Thr); it was shown that the carbon from glutamic acid was assimilated, while the carbon from glucose was dissimilated. Copyright © 2006 Society of Chemical Industry     

Diffusion of glutamic acid in relation to growth of Geotrichum candidum and Penicillium camembertii at the surface of a solid medium

Growth of pure cultures of Geotrichum candidum or Penicillium camembertii at the surface of a solid medium was studied. Consumption of nutrients by the microorganisms growing at the surface of the gel induced their diffusion from the core to the rind. Particular attention was paid to the diffusion of glutamic acid, the nitrogen source, in relation to the growth of the microorganism at the surface. The growth kinetic has been described using the Verlhust model. The diffusion coefficient of glutamic acid in sterile culture medium was measured and found to be 0.55 cm² day^?1. With this coefficient and assuming that the glutamic acid consumption was partially linked to growth, the experimental diffusion gradients have been fitted. Good agreement was found between experimental data and the diffusion/reaction model. The glutamic acid diffusion cannot be assumed to limit growth, since noticeable amounts of this substrate always remained at the upper surface of the gel. Copyright © 2004 Society of Chemical Industry     

Carbon assimilation and dissimilation during growth of Geotrichum candidum on amino acids and glucose

BACKGROUND: This work examines the metabolic behaviour of amino acids during Geotrichum candidum growth, in the presence of a primary carbon source like glucose. Amino acids were characterized based on their carbon assimilation and dissimilation by G. candidum, in the presence of glucose as the limiting substrate. RESULTS: The first group (Cys, His, Phe, Thr and Trp) was only used as nitrogen sources by G. candidum, with glucose being the carbon and energy source. Glucose repression was shown for the rest of the amino acids, since only after glucose depletion amino acids from the second group (Gly, Lys, Met, Val) were dissimilated for energy supply by oxidation into CO₂, while those from the third group (Ala, Arg, Asp, Glu, Leu, Pro and Ser) were assimilated as carbon sources (and additionally used as nitrogen sources), leading to a diauxic growth. CONCLUSION: This energy‐saving response was not previously shown for the second fungus involved in ripening of soft white cheese—P. camembertii—leading to simultaneous use of some amino acids and glucose as carbon and energy sources, and hence lower growth rates than those recorded during G. candidum growth. Copyright © 2007 Society of Chemical Industry     

间歇过程能量平衡和(火用)平衡分析方法的研究

通过分析间歇过程的用能特点,以能量演化为线索,在连续过程用能“三环节”模式基础上,提出了基于时间因素的间歇过程“三环节”用能模式和 平衡模式。建立了能量平衡和 平衡方程式。通过分析三个环节之间及整个体系与外界能量关系的模式,分析体系及三个环节间 平衡的关系,揭示了间歇过程的三个环节间密切的相互联系和相互制约的关系。深入剖析了间歇过程的用能规律,揭示了能量在间歇过程体系中的演化和变化的本质。为间歇过程的优化设计和节能降耗提供理论依据。     

Unstructured model for seed cultures without pH control of Lactobacillus helveticus growing on supplemented whey permeate

In cultures of Lactobacillus helveticus with pH controlled at 5.9, growth and lactic acid production were under the control of nutritional limitations (carbon and nitrogen). In the absence of pH control, as was the case for seed cultures, an inhibitory effect on growth of both pH and the undissociated lactic acid concentration were evident before nutritional limitations. The variations of the specific growth rate with the undissociated lactic acid concentration followed exponential decay. Then, the inhibitory effect of pH was also taken into account through the Henderson–Hasselbach equation. The specific growth rate history has been previously found to follow sigmoidal variation. Integration of these relationships gave the theoretical biomass and lactic acid production kinetics. The model fitted experimental kinetic data well and allowed fine analysis of the various growth phases, since the growth‐associated, the deceleration and the stationary states can be characterized by means of the model parameters. © 2002 Society of Chemical Industry     

Batch and continuous reactors for the production of novolacs

The behaviour of batch and continuous reactors for the production of standard novolacs is discussed theoretically. A kinetic model valid from low to high formaldehyde conversions is used. Results show the influence of the formaldehyde/phenol molar ratio as well as the stated formaldehyde conversion on the composition of the resulting novolac. For the limit of complete segregation, a series of three ideal stirred tanks are shown adequate for the continuous industrial production, at total mean residence times equivalent to those of batch reactors. The influence of partial micromixing is discussed.     

Analysis of the kinetics of growth and lactic acid production for Lactobacillus helveticus growing on supplemented whey permeate

Growth of Lactobacillus helveticus on supplemented whey permeate was divided into five phases: lag, exponential, deceleration, stationary and decline phases. Each phase was characterized by simple model kinetics. From this and by considering a partial association of lactic acid production with growth, with an additional term introduced to account for cessation of production when the carbon substrate became limiting, the lactic acid production was analytically deduced for each growth phase. For both growth and production data, on the whole culture, the calculated values were found to match experimental data. All the model parameters can be easily deduced from experimental data. The model allows therefore a fine analysis of growth and production kinetics. Copyright © 2005 Society of Chemical Industry     

The effect of specific growth rate and death rate on monoclonal antibody production in hybridoma chemostat cultures

Experimental data collected from bench-scale chemostat cultures of mouse-mouse hybridoma cells have been used for the development of a kinetic model of monoclonal antibody production. The specific antibody productivity was found to be proportional to the specific death rate, indicating a stimulating effect of stress on the ability of the cells to produce antibody. The death rate was found to be an exponential function of the average cell age in the culture. Furthermore, a Generalized Maintenance Energy (GME) model is proposed, to take account of the effects of culture stress on the nutrient uptake rates. The proposed relationships agreed very well with other mouse-mouse hybridoma chemostat culture data in the literature.     

Carbon- and nitrogen-limited growth of Penicillium chrysogenum in fed batch culture: The optimal ammonium ion concentration for penicillin production

Fed batch culture was used to investigate penicillin production when the growth of Penicillium chrysogenum was limited by the supply of either sucrose and or ammonium ions. It was found that a ‘quasi steady state’ (in which the growth rate was virtually equal to the dilution rate) could be established under these conditions. Some metabolic parameters (specific sucrose consumption rate and growth yields) were dependent on the ratio of sucrose: ammonium ions in the feed medium over a range of ammonium concentrations both above and below the double substrate-limited point. The maximum specific rate of penicillin production required the supply of a large excess of ammonium ion, about five times the growth-limiting level. That is, the ratio of ammonium-nitrogen: sucrose, fed to the (sucrose-limited) culture, was 0.11 and the residual ammonium ion concentration was in excess of 18 mmol dm^?3, at a dry biomass concentration of 0.6%.     

Effect of ammonium chloride on plasmid DNA production in high cell density batch culture for biopharmaceutical use

In this paper the influence of ammonium salt concentration on the production of pharmaceutical grade plasmid DNA from unfed high cell density batch culture on synthetic glycerol media is presented. Ammonium chloride in different concentrations (0 mmol dm^?3, 18.7 mmol dm^?3, 37 mmol dm^?3 and 74 mmol dm^?3 supplemented) was used beside sodium glutamate as nitrogen source. Plasmid DNA concentrations of more than 50 mg dm^?3 were obtained with 37 mmol dm^?3 ammonium. The homogeneity of the DNA produced was confirmed by agarose and capillary gel electrophoresis and found to fulfil the quality requirements set for biopharmaceutical plasmid DNA with more than 90% in the supercoiled form. Copyright © 2003 Society of Chemical Industry     

Mathematical model of growth and polyhydroxybutyrate production using microbial fermentation of Bacillus subtilis

Poly-3-hydroxybutyrate (PHB) has been extensively utilized as a biodegradable plastic. The value of substrate inhibition constant (K_I) was also established in shake flask cultures by varying the initial glucose concentration (20–160?g/L) in growth media. Excess carbon source adversely affected the growth of Bacillus subtilis cultures. The production kinetics of PHB was studied using batch fermentation strategy for B. subtilis culture. Batch cultivation was also performed in a 5-L stirred tank bioreactor to obtain a Biomass and PHB yield of 5.25 and 1.6?g/L, respectively. The kinetic data of biomass, PHB production, and substrate consumption was used to estimate the optimized values of the growth and product formation kinetic parameters. Optimal values of kinetic parameters (µ_m value of 0.325, K_S value of 10.53?g/L for glucose, Y value of 0.183?g/g of glucose, K_I value of 105?g/L, m value of 0.12?g/(g h), k₁ of 0.36?g/g, and k₂ value was 0.12?g/(g h)) and the initial values of biomass, substrate and PHB concentration (X?=?0.14?g/L, S?=?9.99?g/L, and P?=?0.13?g/L) were utilized to obtain a modified mathematical model for PHB production. Statistical validity of the mathematical model simulations were measured using F-test. The F-test showed that the statistical validity of the model was more than 95% when compared with experimentally obtained values. This model also predicted that the production of PHB using B. subtilis cultures is mainly growth associated.     

Critical temperature for production of MAG by esterification of different FA with glycerol using <Emphasis Type="Italic">Penicillium camembertii</Emphasis> lipase

Production of MAG by a lipase-catalyzed reaction is known to be effective at low temperature. This phenomenon can be explained by assuming that synthesized MAG are excluded from the reaction system because MAG, which have low m.p., are solidified at low temperatures. Consequently, MAG are efficiently accumulated and do not serve as the precursor of DAG. If this hypothesis is correct, the critical temperature for MAG production, defined as the highest temperature at which DAG synthesis is repressed, should depend on the m.p. of the MAG. Esterification of FFA with glycerol using Candida rugosa, Rhizopus oryzae, and Penicillium camembertii lipases produced MAG efficiently at low temperatures. However, Candida lipase showed very low esterification activity at high temperatures (>20°C), and Rhizopus lipase produced not only MAG but also DAG even at low temperatures. Meanwhile, P. camembertii lipase catalyzed synthesis of MAG only from FFA and glycerol at low temperatures, although the enzyme catalyzed synthesis of DAG from MAG in addition to synthesis of MAG at high temperatures. We thus studied the effect of temperature on esterification of C₁₀−C₁₈ FFA with glycerol using Penicillium lipase as a catalyst and determined the critical temperatures for production of MAG. The critical temperature for production of each MAG showed a linear correlation with m.p. of the MAG, which supported the hypothesis. In addition, because the m.p. of MAG are estimated from that of the constituent FA, the optimal temperature for production of MAG can be predicted from the m.p. of the FFA used as a substrate.     

Batch adsorption of trichlorotrifluoroethane (freon-113) onto activated carbon — surface diffusivity and pore diffusivity

Activated carbon was found more active than molécular sieve 13X and silica gel in adsorbing 1,1,2 trichloro-1,2,2 trifluoroethane (CFE). Batch adsorption experiments were carried out with activated carbon to adsorb CFE at 15, 25 and 30°C. The adsorption isotherms of CFE on activated carbon were of the Langmuir type: q(C) = q_m KC / (1 + KC) where q^m and K were evaluated for the three temperatures. The measured bulk concentration-time data were interpreted equally well with the surface diffusion model and the pore diffusion model; for the former model the surface diffusivity increased with increasing initial CFE concentration, and for the latter the pore diffusivity was independent upon the initial CFE concentration.     

Penicillium commune spore production in solid‐state fermentation of coffee pulp at laboratory scale and in a helical ribbons rotating reactor

Penicillium commune was grown on coffee pulp (CP) by solid‐state fermentation (SSF). The effects of the duration of CP thermal treatment and the effects of incubation temperature on spore production yield were studied at laboratory scale. The effect of mixing during fermentation was assayed at pilot plant scale in a 70 L stainless steel non‐aseptic reactor equipped with helical ribbons for mixing solids. For thermal treatments of CP at 121 °C for 10, 20, 30 and 40 min, no significant difference in spore production yield was observed. Maximum sporulation yield was found at 25 °C; when the incubation temperature was higher than 30 °C, the sporulation yield decreased significantly. A spore production yield of 3.7 × 10⁹ spores g^?1 dry CP was obtained when continuous mixing (0.25 rpm) was used at pilot plant scale; however, a decrease in spore yield (1.4 × 10⁹ spores g^?1 dry CP) was observed under static conditions. Spore production was not affected when a scale factor between 79 and 105 was assayed from laboratory to pilot plant; at this level, the productivity obtained was 3.1 × 10⁷ spores g^?1 dry CP h^?1. This value is similar to that found in other reports using natural substrates but working at a smaller scale. Copyright © 2006 Society of Chemical Industry     

Neural and Hybrid Neural Modeling and Control of Fed‐Batch Fermentation for Streptokinase: Comparative Evaluation under Nonideal Conditions

Fermentations involving competition between two or more kinds of cells under nonideal conditions show complex profiles that are sensitive to the extra‐cellular environment. These fermentations therefore require accurate and rapid on‐line data acquisition and control. However, both on‐line measurements and modelling are difficult and expensive for large bioreactors, thus limiting the usefulness of model‐based control. While neural networks offer an alternative, they require extensive training and can be difficult to optimize for large arrays. Hybrid networks combining a few neural networks with some mathematical equations offer a good compromise. The possibility of using a hybrid model for simulation‐cum‐control has been examined here for the fed‐batch production of streptokinase. Under noideal conditions, hybrid neural models outperformed both mathematical models and arrays of neural networks, thus suggesting their viability for large‐scale fermentation monitoring and control.     

间歇发酵螺孢菌产碱性果胶酶过程动力学研究

以自行筛选获得的螺孢菌ZG9901可以生产用于棉麻织品加工的碱性果胶酶。根据间歇发酵螺孢产碱性果胶酶过程菌体生长和孢子产生等规律，建立了螺孢菌ZG9901产碱性果胶酶过程动力学模型，并以摇瓶和发酵罐间隙发酵过程实验数据拟合了动力学模型参数。建立的模型同时考虑了菌丝体生长与孢子形成与产酶的关系和蛋白酶带来的产物失活。     

A hybrid neural model (HNM) for the on‐line monitoring of lipase production by Candida rugosa

A mechanistic model was proposed by Gordillo for the representation of lipase production by Candida rugosa, with the bioreactor in batch and fed‐batch operation. However, the model was not able to represent the lipolytic activity. The objective of the present study is to propose an efficient hybrid neural‐phenomenological model (HNM) for this process. The experimental data used corresponded to fed‐batch operation with constant substrate feed rate at 2.8 × 10^?7; 5.6 × 10^?7 and 9.7 × 10^?7 kg s^?1. Artificial neural networks (ANNs) were trained to represent the aqueous and intracellular lipase activity and were further associated with a reduced version of the mechanistic model of the proposed HNM. When compared to the experimental data, the HNM exhibited higher accuracy. The HNM can be employed in process monitoring using only on‐line measurements of CO₂ and substrate feed rate to infer enzyme activities and also substrate and biomass concentrations. Copyright © 2007 Society of Chemical Industry