Separation of dilute aqueous butanol and acetone solutions by pervaporation through liquid membranes

A simultaneous extraction-stripping process is proposed for separating volatile products from fermentation broths, it is based on pervaporation through a liquid membrane supported with a hydrophobic porous membrane. The liquid membrane prepared with oleyl alcohol was selected as the most suitable for separating volatile products resulting from acetone-butanol fermentation. The separation performance and stability of the oleyl alcohol liquid membrane were investigated by using dilute aqueous butanol and acetone solutions. The oleyl alcohol liquid membrane was found to be superior by far in both selectivity and permeability of butanol to the better known silicone rubber membrane in its high selectivity for alcohols. Using the oleyl alcohol liquid membrane, the dilute aqueous butanol solutions of around 4 g/L obtained in acetone-butanol fermentation could be concentrated up to 100 times. The stability of this liquid membrane was also quite good as long as the surface tension of the feed solution was less than the critical surface tension of the support membrane. No change in the separation performance was found after the continuous usage in a long period of 100 h.     

Enhanced acetone-butanol fermentation using repeated fed-batch operation coupled with cell recycle by membrane and simultaneous removal of inhibitory products by adsorption

A novel acetone-butanol production process was developed which integrates a repeated fed-batch fermentation with continuous product removal and cell recycle. The inhibitory product concentrations of the fermentation by Clostridium acetobutylicum were reduced by the simultaneous extraction process using polyvinylpyridine (PVP) as an adsorbent. Because of the reduced inhibition effect, a higher specific cell growth rate and thus a higher product formation rate was achieved. The cell recycle using membrane separation increased the total cell mass density and, therefore, enhanced the reactor productivity. The repeated fed-batchoperation overcame the drawbacks typically associated with a batch operation such as down times, long lag period, and the limitation on the maximum initial substrate concentration allowed due to the substrate inhibition. Unlike a continuous operation, the repeated fed-batch operation could beoperated for a long time at a relatively higher substrate concentration without sacrificing the substrate loss in the effluent. As a result, the integrated process reached 47.2 g/L in the equivalent solvent concentration (including acetone, butanol, and ethanol) and 1.69 g/L . h in the fermentor productivity, on average, over a 239.5-h period. Compared with a controlled traditional batch acetone-butanol fermentation, the equivalent solvent concentration and the tormentor productivity were increased by 140% and 320%, respectively. (c) 1995 John Wiley & Sons Inc.     

On-line monitoring and control of acetone-butanol fermentation by membrane-sensor mass spectrometry

A mass spectrometry (MS) membrane sensor was developed and applied to on-line product measurement in acetone-butanol fermentation. The sensor facilitated the monitoring of acetone, butanol, ethanol, H₂ and CO₂, and single-compound calibration curves for both acetone and butanol showed a linear relationship between the product concentration and the MS response. However, when an actual fermentation was monitored, the product concentration calculated from the MS response was smaller than the concentration determined by gas chromatography, and the relationship between the response and the product concentration was nonlinear. It was found that large amounts of gases (H₂, CO₂) entering the MS analyzation chamber were causing a ‘space charge effect’, which resulted in an MS response ceiling. The problem could be resolved by reducing the surface area of the sensor membrane. Under some fermentation conditions, a by-product, n-butyl butyrate, was produced, and this interfered with the measurement of butanol due to a peak overlapping effect. However, it was found that this could be compensated for by using an empirical equation. Application of the MS membrane sensor in a fed batch culture of acetone-butanol fermentation resulted in successful control of the butanol concentration.     

Continuous acetone-butanol fermentation with high productivity by cell ultrafiltration and recycling

To increase the productivity of the acetone-butanol fermentation, a hollow-fiber ultrafilter is used to separate and recycle cells in a continuous fermentation ofClostridium acetobutylicum. Under partial cell recycling and at a dilution rate of 0.5 hr^–1, a cellular concentration of 20 g/l and a solvent productivity of 6.5 g/l.hr is maintained for several days at a total solvent concentration of 13 g/l.     

Action of oligomycin on cultured mammalian cells. Permeabilization to translation inhibitors

Summary Oligomycin, an inhibitor of ATP synthesis, has been used as a model to study the effects of ATP depletion on macromolecular synthesis and modification of membrane permeability. Protein synthesis is totally blocked by the antibiotic, whereas RNA and DNA synthesis are less inhibited. Different concentrations of monovalent and divalent cations do not revert the inhibition of protein synthesis. Measurement of cellular ATP and ⁸⁶Rb⁺ content indicate that the blockade of translation depends on the ATP content. A significant decrease in cellular ATP does not lead to the reduction of monovalent ions in the cell, although hyperpolarization of the cell membrane does take place. An increased membrane permeability to some inhibitors develops when the cells are hyperpolarized by oligomycin.     

Rational optimization of culture conditions for the most efficient ethanol production in Scheffersomyces stipitis using design of experiments

Optimization of culture parameters for achieving the most efficient ethanol fermentation is challenging due to multiple variables involved. Here we presented a rationalized methodology for multi‐variables optimization through the design of experiments DoE approach. Three critical parameters, pH, temperature, and agitation speed, affecting ethanol fermentation in S. stipitis was investigated. A predictive model showed that agitation speed significantly affected ethanol synthesis. Reducing pH and temperature also improved ethanol production. The model identified the optimum culture conditions for the most efficient ethanol production with the yield and productivity of 0.46 g/g and 0.28 g/l h, respectively, which is consistent with experimental observation. The results also indicated the scalability of the model from shake flask to bioreactor. Thus, DoE is a promising tool permitting the rapid establishment of culture conditions for the most efficient ethanol fermentation in S. stipitis. The approach could be useful to reduce process development time in lignocellulosic ethanol industry. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

In silico Prediction of Human Oral Absorption Based on QSAR Analyses of PAMPA Permeability

The parallel artificial membrane permeation assay (PAMPA) was developed as a model for the prediction of transcellular permeation in the process of drug absorption. Our research group has measured the PAMPA permeability of peptide‐related compounds, diverse drugs, and agrochemicals. This work led to a classical quantitative structure–activity relationship (QSAR) equation for PAMPA permeability coefficients of structurally diverse compounds based on simple physicochemical parameters such as lipophilicity at a particular pH (log P_oct and |pK_a?pH|), H‐bond acceptor ability (SA_HA), and H‐bond donor ability (SA_HD). Since the PAMPA permeability of lipophilic compounds decreased with their apparent lipophilicity due to the unstirred water layer (UWL) barrier on membrane surfaces and to membrane retention, a bilinear QSAR model was introduced to explain the permeability of a broader set of compounds using the same physicochemical parameters as those used for the linear model. We also compared PAMPA and Caco‐2 cell permeability coefficients of compounds transported by various absorption mechanisms. The compounds were classified according to their absorption pathway (passively transported compounds, actively transported compounds, and compounds excreted by efflux systems) in the plot of Caco‐2 vs. PAMPA permeability. Finally, based on the QSAR analyses of PAMPA permeability, an in silico prediction model of human oral absorption for possibly transported compounds was proposed, and the usefulness of the model was examined.     

Protonophore anion permeability of the human red cell membrane determined in the presence of valinomycin

Summary A transport model for translocation of the protonophore CCCP across the red cell membrane has been established and cellular CCCP binding parameters have been determined. The time course of the CCCP redistribution across the red cell membrane, following a jump in membrane potential induced by valinomycin addition, has been characterized by fitting values of preequilibrium extracellular pHvs. time to the transport model. It is demonstrated, that even in the presence of valinomycin, the CCCP-anion is well behaved, in that the translocation can be described by simple electrodiffusion. The translocation kinetics conform to an Eyring transport model, with a single activation energy barrier, contrary to translocation across lipid bilayers, that is reported to follow a transport model with a plateau in the activation energy barrier. The CCCP anion permeability across the red cell membrane has been calculated to be close to 2.0×10^–4 cm/sec at 37°C with small variations between donors. Thus the permeability of CCCP in the human red cell membrane deviates from that found in black lipid membranes, in which the permeability is found to be a factor of 10 higher.     

In situ extractive fermentation of acetone and butanol

The productivity of the acetone-butanol fermentation was increased by continuously removing acetone and butanol from the fermentation broth during fed-batch culture. Whole broth containing viable cells of Clostridium acetobutylicum was cycled to a Karr reciprocating plate extraction column in which acetone and butanol were extracted into oleyl alcohol flowing counter-currently through the column. By continuously removing these toxic metabolites from the broth, end product inhibition was reduced, and a concentrated feed solution containing 300 g/L glucose was fermented at an overall butanol productivity of 1.0 g/L h, 70% higher than the productivity of normal batch fermentation. The continuous extraction process provides flexible operation and lends itself to process scale-up.     

Production of acetone-butanol by extractive fermentation using dibutylphthalate as extractant

Extractive fermentation of glucose, glucose-xylose mixtures and hydrolysates of lignocellulosics to acetone-butanol solvents were studied and compared with similar fermentations in the absence of extractant. The extractant selected for this research was dibutylphthalate which, in addition to having satisfactory physical properties for this purpose, is non-toxic and mildly stimulating to the growth of the organism used, Clostridium acetobutylicum P262. Sugar concentrations mainly in the range of 80 to 100 g/l resulted in solvent concentrations of 28 to 30 g/l in 24 h extractive fermentations, compared to 18 to 20 g/l for non-extractive control fermentations. Conversion factors of 0.33 to 0.37 g solvents/g sugar consumed were obtained. Rapid fermentation was achieved by high cell concentrations and cell recycle from each 24 h fermentation to the succeeding similar 24 h fermentation. Somewhat higher nutrients were also helpful. By this means, 255 l of acetone-butanol solvents were obtained per tonne of aspen wood, 298 l per tonne of pine and 283 l per tonne of corn stover. Such high product yields from inexpensive substrates offer the prospect of economic viability for the process.     

Fructan Biosynthesis by Intra‐ and Extracellular Zymomonas mobilis Levansucrase after Simultaneous Production of Ethanol and Levan

The chemical composition of the Zymomonas mobilis biomass and the culture liquid after ethanol and levan synthesis were studied. The activities of intra‐ and extracellular levansucrase produced by the Z. mobilis strain 113 “S” under optimum conditions both for levan and fructooligosaccharide (FOS) synthesis were also determined. It was shown that levan production relates to the reduction of the carbohydrate and lipid content in the biomass by increasing the nucleic acid and protein content. The levan producing activity of cellular levansucrase after ethanol and levan synthesis was approximately 30–40% of the total activity in the second fermentation stage. It was established that the cell free culture liquid, containing ethanol, levan, gluconic acid and sucrose (15%) at 25 °C, did not show any additional levan synthesising activity. At optimum FOS synthesis conditions (45 °C and 70% sucrose), the cell‐free culture liquid exhibited a high FOS synthesising activity (31% from total carbohydrates), with slightly reduced biomass activity. It was concluded that as a result of the simultaneous ethanol and levan production, the remaining biomass as well as the cell‐free culture liquid could be used for FOS production.     

Uptake and activation of acetate and butyrate in Clostridium acetobutylicum

Summary The pathway for uptake of acids during the solvent formation phase of an acetone-butanol fermentation by Clostridium acetobutylicum ATCC 824 was studied. ¹³C NMR investigations on actively metabolizing cells showed that butyrate can be taken up from the medium and quantitatively converted to butanol without accumulation of intermediates. The activities of acetate phosphotransacetylase, acetate kinase and phosphate butyryltransferase rapidly decreased to very low levels when the organism began to form solvents. This indicates that the uptake of acids does not occur via a reversal of these acid forming enzymes. No short-chain acyl-CoA synthetase activity or butyryl phosphate reducing activity could be detected. Based on our results and a critical analysis of literature data on acetone-butanol fermentations, it is suggested that an acetoacetyl-CoA: acetate (butyrate) CoA-transferase is solely responsible for uptake and activation of acetate and butyrate in C. acetobutylicum. The transferase exhibits a broad carboxylic acid specificity. The key enzyme in the uptake is acetoacetate decarboxylase, which is induced late in the fermentation and pulls the transferase reaction towards formation of acetoacetate. The major implication is that it is not feasible to obtain a batch-wise butanol fermentation without acetone formation and retention of a good yield of butanol.     

Indirect method for quantification of cellular biomass in a solidscontaining medium used as pre-culture for cellulase production

A process that combines the advantages of solid state fermentation (SSF) and submerged fermentation (SmF) could increase the efficiency of cellulase production required in the cellulosic ethanol industry. Due to the difficulty of measuring cellular biomass in the presence of solids, we developed a novel methodology for indirect quantification of biomass during production of the preculture for a combined fermentation process. Cultivation of Aspergillus niger was initiated as SSF using sugar cane bagasse as a solid substrate. Experiments were conducted in the absence of bagasse to determine growth kinetic parameters. Changes in glucose and biomass concentrations were measured. and the data were used for simulation employing a simple unstructured model. Parameters were estimated by applying a combination of Simulated Annealing (SA) and Levenberg-Marquardt (LM) algorithms to search for minimization of the error between model estimates and experimental data. Growth kinetics followed the Contois model, with a maximum specific growth rate (μ_max) of 0.042/h, a yield coefficient for biomass formation (Y_x/s) of 0.30 g/g and a death constant (k_D) of 0.005/h.These parameters were used to simulate cellular growth in the solids-containing medium. The proposed model accurately described the experimental data and succeeded in simulating the cell concentration profile. The selected pre-culture conditions (24 h as SSF followed by 48 h as SmF) were applied for cellulase production using the combined fermentation process and resulted in an endoglucanase activity (1,052 ± 34 U/L) greater than that obtained using the conventional SmF procedure (824 ± 44 U/L). Besides the standardization of pre-culture conditions, this methodology could be very useful in systems where direct measurement of cell mass is not possible.     

Electrophysical monitoring of culture process of recombinant Escherichia coli strains

A novel method for monitoring the cell culture process has been developed. The method is based on the measurements of electro-optical characteristics of cell suspension, calculation of cell structure parameters, and the relationship between accumulation of proteins and change of these parameters' employment. Application of the method for the monitoring of a culture process of a recombinant strain is considered. The process of growth of recombinant strains cannot be sufficiently predicted and the direct measurement of cell culture parameters is unlikely to be the most efficient way of solving the problem.Escherichia coli plasmid-free and recombinant strains synthesizing the fusion protein consisting of tumor necrosis factor-alpha (TNF) and thymosin-alpha(1) (T) were studied. It was found that cytoplasmic electroconductivity of the strains investigated increased during the culture process. The accumulation of insoluble recombinant pThy-315-encoded hybrid protein TNF(SINGLEBOND)T in cells resulted in a decrease of the membrane dielectric permeability. To determine variations of membrane dielectric permeability the amount of insoluble recombinant protein TNF(SINGLEBOND)T in the bacterial cells should be calculated.     

Use of fluorometry for monitoring and control of a bioreactor

A new fluorescent bioreactor monitoring probe-multiple excitation fluorometric system (MEFS)-has been developed. This probe was compared to the commercially available BioChem Technology FluroMeasure system (NADH probe). In this task the fluorescence behavior of three model fermentation systems, ethanol fermentation by Candida utilis, phenol fermentation by Pseudomonas putida, and glucose fermentation by Saccharomyces cerevisiae, were examined. The results indicated that the fluorescence intensity and behavior of various cellular fluorophors vary significantly between the different fermentation systems. Monitoring a fermentation process using only NAD(P)H fluorescence provided limited information. The NAD(P)H fluorescence was found not to be the best fluorescence signal for monitoring cell concentrations. The best way of monitoring a bioreactor by fluorometry may be to monitor several fluorophors in the whole culture broth simultaneously and to relate these fluorescence signals to various biological parameters.     

The fermentative production of acetone-butanol by Clostridium acetobutylicum.

Fourteen different media were used in the fermentative production of acetone-butanol. The highest total yields were achieved in medium I. Potato starch and soluble starch were suitable as carbon sources. The best concentrations of potato starch and soluble starch were 500.0 and 10.0 g/l, respectively. Peptone was the most favourable nitrogen source. The best concentration of peptone was 4.0 g/l. Calcium carbonate in 3.6 g/l acted as buffering agent in the fermentation process. The best initial pH value of the fermentation medium was 6.0. The optimum temperature was 32--33degreesC. The fermentation process required 120 h to obtain maximum yields of acetone-butanol.     

Metabolism analysis and on-line physiological state diagnosis of acetone-butanol fermentation

Fermentation equations for acetone-butanol (AB) were applied in a metabolic analysis of the reaction network under various conditions; that is, at different pHs and a high NADH2 turnover rate using methyl viologen, in a Clostridium acetobutylicum culture. The results disclosed variations in the pattern of rate changes that reflected changes in the physiological state. A linear relationship was found to exist between NADH2 generation and butanol production rate. By coupling an automated measurement system with the fermentation model, on-line estimation of the culture state was accomplished. Based on the AB fermentation model, new parameters were defined for on-line diagnosis of the physiological state and determination of the best timing for amplifying NADH2 generation by the addition of methyl viologen to obtain a high level of butanol productivity. A potential means of achieving optimal control for a high level of solvent production, involving the correlation of certain rates, is proposed.     

Inhibition of membrane functions in intact HeLa cells byClostridium difficile cytotoxic culture filtrates

The basis for cytotoxicity to intact HeLa cells by culture filtrates ofClostridium difficile has been investigated. Decrease in intracellular K⁺ levels and inhibition of -aminoisobutyric acid uptake were detected first after exposure to filtrates, followed by inhibition of macromolecular synthesis. Twenty-five percent of the K⁺ remained associated with the cell monolayer, and amino acid uptake and macromolecular synthesis were not totally abolished. These results indicate thatC. difficile culture filtrates preferentially inhibited membrane functions, either by exhausting ATP supplies or by disrupting the permeability barrier of the cell.     

Enhanced production of CoQ<Subscript>10</Subscript> by newly isolated <Emphasis Type="Italic">Sphingomonas</Emphasis> sp. ZUTEO3 with a coupled fermentation–extraction process

The use of coenzyme Q₁₀ (CoQ₁₀) as a complementary therapy in heart failure will increase in proportion to the growth of the ageing population and the expansion of statins consumption. Economical production of CoQ₁₀ by microbes will become more important due to the growing demands of the pharmaceutical industry. Process simplification and integration might be one desirable pathway for economic production of CoQ₁₀ by microbial fermentation. In this report, the effect of a coupled fermentation–extraction process on CoQ₁₀ production by newly isolated Sphingomonas sp. ZUTEO3 was evaluated. It was found that the CoQ₁₀ yield of the coupled process was significantly higher than that of the traditional process. As optimal conditions in our experiment, 2% soybean oil was added to the original culture to enhance cell membrane permeability, and 50 mL hexane was added to the 30 h culture as an extracting solvent for the subsequent coupled fermentation–extraction process. The maximal yield of CoQ₁₀ reached 43.2 mg/L and 32.5 mg/g dry cell weight after 38 h of total fermentation period. The coupled process represents one potential pathway for CoQ₁₀ production with even higher yield and lower cost. This is the first report of CoQ₁₀ production by Sphingomonas sp. using a coupled fermentation–extraction process.     

Application of process mass spectroscopy to the detection of metabolic changes in plant tissue culture

There is a clear need in the area of plant cell culture for methods of on-line estimation of culture parameters. The introduction of plant cells into culture can result in a loss of their photoautotrophic character so that they are largely heterotrophic. As a result, fermentation off-gas analysis may not be confounded by photosynthetically-related O₂ production. In this study performance of a suspension culture of Syringa vulgaris, in a pneumatically agitated bioreactor of in-house design, was investigated. The effect of light on growth, carbohydrate metabolism and the respiratory quotient (RQ), determined by process mass spectroscopy, was studied. Yield coefficients for cells grown in the light and dark were similar although the patterns of carbohydrate uptake were quite different. Maximum biomass yields were higher in this bioreactor than normally observed in shake flasks. The RQ was dynamic during the course of the fermentation, peaking during the transition from the lag phase to the growth phase. It is suggested that the RQ may prove useful as an on-line parameter for monitoring transitions in cellular metabolism during plant cell culture fermentations.Abbreviations RQ respiratory quotient - v.v.m. volume of gas fed to fermenter per unit volume per minute - Y_X/S growth yield coefficient based on total carbohydrate