The Escherichia coli K-12 strain TG1 was grown at 28 degrees C in aerobic glucose-limited continuous cultures at dilution rates ranging from 0.044 to 0.415 h(-1). The rates of biomass formation, the specific rates of glucose, ammonium and oxygen uptake and the specific carbon dioxide evolution rate increased linearly with the dilution rate up to 0.3 h(-1). At dilution rates between 0.3 h(-1) and 0.4 h(-1), a strong deviation from the linear increase to lower specific oxygen uptake and carbon dioxide evolution rates occurred. The biomass formation rate and the specific glucose and ammonium uptake rates did not deviate that strongly from the linear increase up to dilution rates of 0.4 h(-1). An increasing percentage of glucose carbon flow towards biomass determined by a reactor mass balance and a decreasing specific ATP production rate concomitant with a decreasing adenylate energy charge indicated higher energetic efficiency of carbon substrate utilization at higher dilution rates. Estimation of metabolic fluxes by a stoichiometric model revealed an increasing activity of the pentose phosphate pathway and a decreasing tricarboxylic acid cycle activity with increasing dilution rates, indicative of the increased NADPH and precursor demand for anabolic purposes at the expense of ATP formation through catabolic activities. Thus, increasing growth rates first result in a more energy-efficient use of the carbon substrate for biomass production, i.e. a lower portion of the carbon substrate is channelled into the respiratory, energy-generating pathway. At dilution rates above 0.4 h(-1), close to the wash-out point, respiration rates dropped sharply and accumulation of glucose and acetic acid was observed. Energy generation through acetate formation yields less ATP compared with complete oxidation of the sugar carbon substrate, but is the result of maximized energy generation under conditions of restrictions in the tricarboxylic acid cycle or in respiratory NADH turnover. Thus, the data strongly support the conclusion that, in aerobic glucose-limited continuous cultures of E. coli TG1, two different carbon limitations occur: at low dilution rates, cell growth is limited by cell-carbon supply and, at high dilution rates, by energy-carbon supply.

Degradation of phenol and benzoic acid was studied in a fluidized-bed reactor (liquid volume 2.17 L) under nonsterile conditions with special emphasis on maximizing the flow through the reactor and investigating reactor performance at fluctuating feeds. Reactor response to substrate pulses was investigated by applying substrate square-wave inputs at a liquid flow of 1.00 L h(-1). A twofold increase of the phenol and benzoic acid feed concentrations for 2.5 h did not lead to accumulation and breakthrough. The cells were able to survive four to fivefold increases of the feed concentration for 1 h without loss of viability, although the phenol pulse lead to phenol accumulation in the reactor. Reactor performance at constantly fluctuating loads was investigated by varying the feed concentrations using sine wave functions. No accumulation of phenol or benzoic acid was observed. Influence of induction was studied using shift experiments. After 35 days of operation (369 hydrodynamic residence times) with phenol as sole substrate (carbon source) the reactor was able to mineralize benzoic acid without any adaptation or lag phase. The capability of phenol degradation, on the other hand, was lost by most cells after only 3 days operation with benzoic acid as the sole substrate. The experiments underline the importance of induction. In order to maximize the flow through the reactor, the liquid flow was increased stepwise while the feed concentrations were reduced correspondingly, keeping the volumetric conversion rates of phenol (0.24 g L(-1) h(-1)) and benzoic acid (0.17 g L(-1) h(-1)) constant. By this means, liquid flow could be increased up to 13.32 L h(-1), which was more than 20-fold higher than the maximum liquid flow achievable in a chemostat using the same conditions.

Plasmid stability of recombinant Pseudomonas sp. B13 FR1 pFRC20P, a strain capable of mineralizing 3- and 4-chlorobenzoate and 4-methylbenzoate, was investigated in continuous culture. The hybrid cosmid pFRC20P enables the strain to mineralize 4-methylbenzoate. Rapid plasmid loss was observed under nonselective conditions using 3-chlorobenzoate as the substrate. Plasmid stability decreased with increasing dilution rate. Despite the growth advantage of the generated plasmid free cells a total depletion of plasmid bearing cells was not observed. After approximately 50 generations the fraction of plasmid bearing cells reached a constant level of 10%, which was stably maintained during the next 25 generations. Cells from this stage were used to inoculate a new culture that resulted in a stable level of 50% plasmid bearing cells. By a temporary substrate change to selective conditions (4-methylbenzoate), this level could be further increased to 70%. Literature models on plasmid stability could not be applied to describe the experimental data. Therefore, a new but unstructured model was developed to describe the experimental results. The model is based on the existence of three subpopulations: a plasmid free one, an original plasmid bearing one with a growth disadvantage compared to plasmid free cells, and a second plasmid bearing subpopulation with increased stability that is generated from the original one and has a growth rate comparable to the plasmid free cells.

Quinoline degradation by Comamonas acidovorans was investigated in a three phase fluidized bed reactor at dilution rates below and above the critical value (micro(max) = 0.42 h(-1)). Quinoline was used as the sole source of carbon, nitrogen, and energy. Two attachment carriers, polyurethane foam (Bayvitec) and modified cellulose (Aquacel), and a gel entrapment carrier (polyvinyl alcohol) were studied and compared with regard to their effectiveness to immobilize cells. Attachment and biofilm formation was best at higher dilution rates, regardless of carrier type used. Except for the maximum biomass concentration on the carrier, Y(V) (biomass per volume of solid particles), there was no significant difference in reactor performance between the investigated carriers under stationary conditions. The highest value for Y(V) was found for the gel entrapment carrier (Y(V) = 35 g L(-1)). In a long-term run (66 days), the gel entrapment carrier established a permanent biofilm on the surface of the gel beads after 900 h of cultivation time. Complete quinoline mineralization was achieved at a dilution rate of 2.0 h(-1), which is 4.7 times higher than the critical dilution rate. Identical substrate overloads were applied to the gel entrapment and the cellulose carrier by a step increase of the quinoline feed concentration at a dilution rate of 0.8 h(-1) (D approximately 2micro(max)). The cells survived the overload, but the accumulation of quinoline and quinoline degradation products and the degradation efficiency were different for the two systems during the overload, showing the influence of the carrier type on the dynamic performance and stability of the process.

Multiplicity of steady states of a continuous culture with an inhibitory substrate was used to estimate kinetic parameters under steady-state conditions. A continuous culture of Pseudomonas cepacia G4, using phenol as the sole source of carbon and energy, was overloaded by increasing the dilution rate above the critical dilution rate. The culture was then stabilized in the inhibitory branch by a proportional controller using the carbon dioxide concentration in the reactor exhaust gas as the controlled variable and the dilution rate as the manipulated variable. By variation of the set point, several unstable steady states in the inhibitory branch were investigated and the specific phenol conversion rates calculated. In addition, phenol degradation was investigated under substrate limitation (chemostat operation).The results show that the phenol degradation by P. cepacia can be described by the same set of inhibition parameters under substrate limitation and under high substrate concentrations in the inhibitory branch. Biomass yield and maintenance coefficients were identical. Fitting of the data to various inhibition models resulted in the best fit for the Yano and Koga equation. The well-known Haldane model, which is most often used to describe substrate inhibition by phenol, gave the poorest fit. The described method allows a precise data estimation under steady-state conditions from the maximum of the biological reaction rate up to high substrate concentrations in the inhibitory branch. Inhibition parameter estimation by controlling unstable steady states may thus be useful in avoiding discrepancies between data generated by batch runs and their application to continuous cultures which have been often described in the literature. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 567-576, 1997.

Degradation of 3-chlorobenzoic acid (3CB), 4-chlorobenzoic acid (4CB), and 4-methylbenzoic acid (4MB) as single substrates (carbon sources) and as a substrate mixture were studied in batch and continuous culture using the genetically modified microorganism Pseudomonas sp. B13 FR1 SN45P. The strain was able to mineralize the single compounds as well as the substrate mixture completely. Conversion of the three compounds in the substrate mixture proceeded simultaneously. Maximum specific substrate conversion rates were calculated to be 0.9 g g(-1) h(-1) for 3 CB and 4CB and 1.1 g g(-1) h(-1) for 4MB. Mass balances indicated the transient accumulation of pathway intermediates during batch cultivations. Hence, the rate limiting step in the degradative pathway is not the initial microbial attack of the original substrate or its transport through the cell membrane. Degradation rates on 3CB were comparable to those of the parent strain Pseudomonas sp. B13. The stability of the degradation pathways of strain Pseudomonas sp. B13 FR1 SN45P could be demonstrated in a continuous cultivation over 3.5 months (734 generation times) on 3CB, 4MB, and 4CB, which were used as single carbon sources one after the other.

Chemie Ingenieur TechnikVolume 68, Issue 9 p. 1169-1169 GVC-Jahrestagung 160. Mikrobieller Abbau von Chinolin im Dreiphasen-Wirbelschicht-Bioreaktor Dipl.-Ing. U. Kies, Dipl.-Ing. U. Kies (Am Poster) Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorDr.-Ing. C. Buchtmann, Dr.-Ing. C. Buchtmann Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorDr. V. Hecht, Dr. V. Hecht Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorProf. Dr. W.-D. Deckwer, Prof. Dr. W.-D. Deckwer Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this author Dipl.-Ing. U. Kies, Dipl.-Ing. U. Kies (Am Poster) Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorDr.-Ing. C. Buchtmann, Dr.-Ing. C. Buchtmann Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorDr. V. Hecht, Dr. V. Hecht Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorProf. Dr. W.-D. Deckwer, Prof. Dr. W.-D. Deckwer Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this author First published: September 1996 https://doi.org/10.1002/cite.3306809162AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume68, Issue9September 1996Pages 1169-1169 RelatedInformation

Chemie Ingenieur TechnikVolume 68, Issue 9 p. 1169-1169 GVC-Jahrestagung 161. Inhibierungsparameter für quasi-stationäre Bedingungen am Beispiel des Phenolabbaus durch Pseudomonas cepacia G4 Dipl.-Ing. M. Schröder, Dipl.-Ing. M. Schröder (Am Poster) Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorDipl.-Chem. C. Müller, Dipl.-Chem. C. Müller Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorDr. C. Posten, Dr. C. Posten Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorDr. V. Hecht, Dr. V. Hecht Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorProf. Dr. W.-D. Deckwer, Prof. Dr. W.-D. Deckwer Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this author Dipl.-Ing. M. Schröder, Dipl.-Ing. M. Schröder (Am Poster) Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorDipl.-Chem. C. Müller, Dipl.-Chem. C. Müller Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorDr. C. Posten, Dr. C. Posten Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorDr. V. Hecht, Dr. V. Hecht Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this authorProf. Dr. W.-D. Deckwer, Prof. Dr. W.-D. Deckwer Gesellschaft für Biotechnologische Forschung mbH, D-38124 BraunschweigSearch for more papers by this author First published: September 1996 https://doi.org/10.1002/cite.3306809163AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume68, Issue9September 1996Pages 1169-1169 RelatedInformation

Substrate inhibition is an important situation in the degradation of pollutants and xenobiotics. Short term adaptation of the cells and lacking model validation in batch experiments will lead to erroneous results making experiments in continuous cultivation necessary. Resulting unstable reactor dynamics can be stabilized employing model predictive control. Two examples are shown, namely degradation of phenol and degradation of quinoline. In the first case, a precise determination of substrate uptake kinetics including substrate inhibition is obtained. In the latter case, intermediates can diffuse through the cell membrane and accumulate in the medium. This makes intracellular metabolite concentrations observable without expensive analytics. This interesting feature is accompanied by increased problems in model validation. Model discrimination and parameter estimation are shown to be possible only under substrate inhibited steady state conditions. Experimental and modeling results are shown.

Quinolie degradation by Comamonas acidovorans was studied in a continuously operated three‐phase airlift reactor. Porous glass beads were applied as support matrix for cell imobilization by colonization. Under steady‐state conditions ( S ∼ 0), cell attachment was poor at low dilution rates but imporved considerably with increasing dilution rate. Conversion of quinoline was investigated below and above the washout for suspended culture ( D crit = μ max = 0.42 h −1 ). With immobilized cells the reactor could be operated at D > μ max , and complete conversion of quinoline was achieved as long as the specific quinoline feed rate D * S 0 / X did not exceed the maximum specific degradation rate ( r S , max ). The biofilm thickness was about 100 μm, and its efficiency was about 54% compared to suspended organisms. If quinoline overloads were supplied to the reactor, quinoline, as overloads were supplied to the reactor, quinoline, as well as its pathway intermediates, appeared in the reactor and conversion was low. Hence, the immobilized microorganisms remained viable and active. They could survive quinoline overloads. If the quinoline feed rate was reduced agains, complete conversion was reestablished. © 1995 John Wiley & Sons, Inc.

A bubble column bioreactor was used as bioscrubber to carry out a feasibility study for the cometabolic degradation of trichloroethylene (TCE). Phenol was used as cosubstrate and inducer. The bioreactor was operated like a conventional chemostat with regard to the cosubstrate and low dilution rates were used to minimize the liquid outflow. TCE degradation measurements were carried out using superficial gas velocities between 0.47and 4.07 cm s(-1) and TCE gas phase loads between 0.07 and 0.40 mg L(-1) Depending on the superficial gas velocity used, degrees of conversion between 30% and 80% were obtained. A simplified reactor model using plug flow for the gas phase, mixed flow for the liquid phase, and pseudo first order reaction kinetics for the conversionof TCE was established. The model is able to give a reasonable approximation of the experimental data. TCE degradation at the used experimental conditions is mainly limited by reaction rate rather than by mass transfer rate. The model can be used to calculate the reactor volume and the biomass concentration for a required conversion. (c) 1995 John Wiley & Sons Inc.

An estimation of the true growth yields and maintenance coefficients for Comamonas acidovorans DSM 6426 under continuous cultivation on quinoline has been performed. The data were checked for consistency using available electron, carbon and nitrogen balances. The true biomass energetic yields, eta(max), and energetic maintenance coefficients, m(e), were estimated using two models based on control of growth rate and control of substrate uptake rate, respectively. The estimations were converted to the various familiar true growth yield and maintenance units such as substrate-based (Y-X/S(max), m(S/X)), oxygen-based (Y-X/O2(max), m(O2/X)) and carbon dioxide-based (Y-X/CO2(max), m(CO2/X)) units. For the complete mineralization of quinoline by C. acidorvorans, values of eta(max) = 0.371 and m(e) = 0.0426 h(-1) were obtained.

Analysis of the growth of Pseudomonas cepacia G4 on phenol in continuous culture has been carried out. The data were checked for consistency using both available electron and carbon balances. Coupled with the covariate adjustment estimation technique, the best estimates for true biomass energetic yield, eta(max) and maintenance, m(e), were obtained when the carbon dioxide measurements were excluded. However, upon making corrections to the gas measurements, the best estimates were the maximum likelihood estimates (MLE) based on the complete data. The method therefore allows discrimination to be made between data. Also, similar estimates were obtained using Pirt's model based on the Monod approach and a modified form based on substrate uptake rate being the limiting factor. For the aerobic growth of P. cepacia G4 on phenol, eta(max) = 0.417 and m(e) = 0.0513 h-1 were obtained when the CO2 data were excluded. When corrections were made to the gas measurements to take into account the dissolved CO2 and the effect of operating temperature, eta(max) = 0.432 and m(e) = 0-0684 h-1 were obtained. From the 95% confidence intervals, a maximum of about 38-47.5% of the energy contained in phenol is incorporated into the biomass while the balance (52.5-62%) is evolved as heat with only a little energy needed for the maintenance of the organism.

The microbial degradation of quinoline by Comamonas acidovorans was studied in a laboratory scale stirred tank reactor. In continuous culture experiments using quinoline as a sole source of carbon and nitrogen, it was shown by means of mass balances that quinoline was converted completely to biomass, carbon dioxide, and ammonia. Degradation rates up to 0.7 g/L h were obtained. Measured yield coefficients Y(x/s) for quinoline were about 0.7 g/g, which is in agreement with the theoretical value for complete mineralization. Kinetic constants based on Haldane substrate inhibition were evaluated. The values were micro(max) = 0.48 h(-1), K(i) = 69 mg/L, and K(s) < 1.45 mg/L.

Abstract The aim of this paper is to quantify the emissions from food, drink and metal degreasing industries, and to discuss the potential for biotechnological abatement of VOCs from these sources. The combined emission from these industries was estimated at 600 ktonne per year, although our estimates of data quality suggest that further measurements are required to verify this figure. The biodegradability of the emissions from these industries were reviewed and the need for further research was identified.

To study the influence of ammonium on an antibiotic cultivation, mass transfer measurements of ammonium through microporous hydrophobic membranes using different stripping methods were carried out and compared. The higher overall mass transfer coefficients for ammonium were obtained with an acid stripping solution compared to water, vacuum, or sweeping air. A hollow fiber module for in situ removal of ammonium during cultivation was designed and operated in an external bypass to a 10-L fermentor. Compared to a control fermentation, the cell dry mass could be increased 2.6 times and the antibiotic concentration 8 times, if the in situ ammonium removal was in operation.

A vortex chamber for continuous adsorption of the antibiotic Myxovirescin A on XAD resins was developed. In this paper the design and use of the vortex chamber in an external bypass of a continuous process is described. Compared with the normal continuous process, the specific production rate of the antibiotic is four to five times higher when the antibiotic is continuously adsorbed. A semicontinuous process could be performed by using two chambers for adsorption and regeneration alternatively.

Based on the experimental measurements of Hecht and Rosen in previously published papers, mathematical models were developed for the continuous and semibatch cultivations of Chaetomium cellulolyticum on glucose and cellulose.

The batch cultivation of Chaetomium cellulyticum on glucose was described by a structured model based on the experimental investigations of Hecht et al. (1982) and Rosen (1982). The Monod model did not give satisfactory results. The structured model takes into account the adaptation of the transport system of cells to the substrate supply. The model parameters identified are presented. The agreement between calculated and measured courses of cell growth is excellent.