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71.
L. T. Chang E. L. McGrory R. P. Elander D. J. Hook 《Journal of industrial microbiology & biotechnology》1991,7(3):175-179
Summary Penicillin V (phenoxymethyl penicillin) is produced by industrial strains ofPenicillium chrysogenum in the presence of phenoxyacetic acid (POAc), a side-chain precursor for the penicillin V molecule. The wild-type strain ofP. chrysogenum produces an undesirable penicillin byproduct,para-hydroxypenicillin V (p-OH penicillin V), in addition to penicillin V, viapara-hydroxylation of POAc and subsequent incorporation of thep-OH phenoxyacetic acid into the penicillin molecule. Most of thep-OH penicillin V is produced late in cycle when the POAc concentration in the medium is nearly depleted. The level ofp-OH penicillin V produced by the control strain ranges up to 10–15% of the total penicillins produced. 3-Phenoxypropionic acid andp-bromophenylacetic acid partially inhibit the formation ofp-OH penicillin V with a minimal effect on penicillin V productivity. Mutants deficient in their ability to hydroxylate POAc were found to produce lower levels ofp-OH penicillin V. Multi-step mutation and screening, starting with the wild-type strain, have culminated in isolation of mutants which producep-OH penicillin V as 1% of the total penicillins with no adverse effect on penicillin V productivity. 相似文献
72.
V. A. Vinci T. D. Hoerner A. D. Coffman T. G. Schimmel R. L. Dabora A. C. Kirpekar C. L. Ruby R. W. Stieber 《Journal of industrial microbiology & biotechnology》1991,8(2):113-119
Summary A lovastatin-hyperproducing culture ofAspergillus terreus was shown to produce several co-metabolites extracted from whole broth. The predominant co-metabolite was the benzophenone, sulochrin, reported to arise from a polyketide biosynthetic pathway. This compound was targeted for elimination by classical mutagenesis and screening. A surface culture method employing microtiter, plates was used to ferment mutants for the primary screen. Qualitative determinations of lovastatin and sulochrin production were achieved by high-performance thin-layer chromatography. A mutant, strain AH6, which produced lovastatin titers equivalent to the parent culture and no detectable sulochrin was isolated. In addition, a lovastatin-hyperproducing mutant designated CB4 was capable of producing 16% more lovastatin and 30% less sulochrin than the parent culture in shake flask fermentations. In a pilot-scale 250-gallon fermentation, strain CB4 gave a 20% increase in lovastatin titer while producing 83% less sulochrin than the parent culture. 相似文献
73.
Summary Production of citric acid from beet molasses at a varying pH profile using cell recycle ofAspergillus niger was investigated. Best results in terms of citric acid concentration, yield, productivity and specific citric acid productivity were obtained with a substrate pH of 3.0. 相似文献
74.
A methodology for the design and evalution of bioprocess control strategies is presented. The strategies manage nutrient supply with demand and vary with the metabolic condition and phase of fermentation operation. Six carbon source addition strategies are based on different combinations of available measurements; they are described and evaluated under different operating conditions for yeast cultivation. It is concluded that a single control strategy is not the most appropriate under all possible operating conditions. An oxygen uptake rate-based control strategy performs better with a mean respiratory quotient (RQ) value less than 1.1 during an oxygen limitation than an ethanol control strategy which had a mean RQ of 14. The designed strategies and an approach of applying the strategy that best matches fermentation conditions consistently enables achievement of high cell densities 78.7 g DCW/L and yields 0.50 g DCW/g glucose as the mean values for three fermentations. 相似文献
75.
Extractive lactic acid fermentation using ion-exchange resin 总被引:6,自引:0,他引:6
Lactic acid fermentation is an end-product-inhibited reaction. The restriction imposed by lactic acid on its fermentation can be avoided by extractive fermentation techniques. Studies were performed by attaching an ion-exchange resin packed column with a 2-L fermentor for separation of lactic acid. The fermentation, in a conventional batch mode, resulted in a lactic acid yield of 0.828 g . g(-1) and a lactic acid productivity of 0.313 g . L(-1) . h(-1). However, these could be further enhanced to 0.929 g . g(-1) and 1.665 g . L(-1) . h(-1) by extractive fermentation techniques. The effect of temperature on extractive fermentation was remarkable and has been included in this work. 相似文献
76.
In production-scale, fed-batch fermentations, feed is often added to a single point at the top of the fermentor, which, combined with poor mixing, results in formation of a "feed zone" rich in nutrients. Frequent exposure of the culture to high concentrations of nutrients in the feed zone for sufficient duration can produce unexpected effects on its performance. The effect of the feed zone was evaluated by conducting aerobic fed-batch fermentations of Saccharomyces cerevisiae with both complex and defined media. The broth was recirculated between a recycle loop and a bench-scale fermentor, and feed was intermittently added into the recycle loop to simulate the circulation of cells through the feed zone. Experiments were carried out for a range of residence times in the recycle loop from 0.5 to 12 min. Biomass yields from the complex-media fermentations were not affected by exposure to high nutrient levels in the recycle loop for residence times up to 12 min. Ethanol consumption was reduced by as much as 50% for residence time in the loop up to 3 min. Very long exposure of yeast cells to excess nutrient levels (12 min) gave acetic acid formation. In a defined medium, the simulated feed zone effect increased biomass yield by up to 10%, but had no effect on ethanol levels. This study indicates that the feed zone effect on biomass yield in yeast fermentation, using complex substrates, will be negligible under fully aerobic conditions. 相似文献
77.
The existence of a yield stress in filamentous fermentation broths has important transport phenomena implications in the design and operation of bioreactors. In this study, the constant shear rate vane method was assessed for directly measuring the yield stress of filamentous Aspergillus niger fermentation broths, as well as model fluids (ketchup, yogurt, and pulp suspensions). The method involved rotating 4-, 6-, and 8-bladed vanes (7.2 cm = height = 15 cm; 4.0 cm = dia. = 6 cm) at speeds of 0.01 to 0.64 rpm in the fluid and plotting the torque as a function of time. Based on visual observations, the consistency of the results with vane type and speed and comparison with previous work on nonbiological samples, it was concluded that the method is an effective and consistent technique for yield stress measurements on filamentous fermentation broths. Based on comparisons with concentric cylinder viscometer results, it was also concluded that the value determined via the vane method was a "static" yield stress (values of up to 28 Pa) which was much greater than the extrapolated (or "dynamic") yield stress determined via the concentric cylinder viscometer. (c) 1992 John Wiley & Sons, Inc. 相似文献
78.
Continuous butanol/isopropanol fermentation in down-flow column reactor coupled with pervaporation using supported liquid membrane 总被引:2,自引:0,他引:2
Continuous butanol/isopropanol fermentation with immobilized Clostridium isopropylicum was performed in a downflow column reactor using molasses as the substrate. In order to prevent product inhibition and at the same time obtain high concentration of the products, the column reactor was coupled with a pervaporation module using a supported liquid membrane. The liquid membrane was prepared with oleyl alcohol nontoxic to the microorganism. In comparison with the continuous fermentation without product removal, the specific butanol production rate was 2 times higher. The butanol concentration in the permeate was 230 kg/m(3), which was about 50 times higher than that in the culture broth. A numerical investigation suggested a further increase in the productivity by improving the module construction. 相似文献
79.
On-line fluorescence-monitoring of the methanogenic fermentation 总被引:2,自引:0,他引:2
On-line in situ fluorescence measurements of the methanogenic fermentation were conducted with reactors receiving either glucose or a mixture of volatile fatty acids as the substrate. The reactors were perturbed from steady-state conditions in order to assess the response of fluorescencemonitoring probes. Two fluorescence-monitoring probes were evaluated over a period of 8 months; they performed in a consistent manner, and their response was not significantly affected by the changes in pH and redox potential encountered during routine reactor operation. A commercially available probe, designed to measure NAD(P)H, demonstrated particular promise for detecting imbalance caused by the entry of air, inhibitor addition and was capable of distinguishing between different substrates. This fluorescence-monitoring probe detected imbalance more rapidly than other on-line measurements such as pH, Eh, or gas production, or off-line measurements such as volatile fatty acid concentration or gas composition. An experimental fluorescence-monitoring probe, designed to measure coenzyme F(420), also showed some promise in this regard. The response of the fluorescence-monitoring probes also revealed details of the metabolic routes in the reactors and the probes represent a useful research tool. For example, a failure to observe the characteristic response of the NAD(P)H-monitoring probe to formate addition during the metabolism of acetate, propionate, or glucose strongly suggests that any formate liberated during their catabolism is degraded via a different route to exogenously added formate. 相似文献
80.
Acetic acid formation in Escherichia coli fermentation 总被引:2,自引:0,他引:2
Theoretical analysis of cellulase product inhibition (by cellobiose and glucose) has been performed in terms of the mathematical model for enzymatic cellulose hydrolysis. The analysis showed that even in those cases when consideration of multienzyme cellulase system as one enzyme (cellulase) or two enzymes (cellulase and beta-glucosidase) is valid, double-reciprocal plots, usually used in a product inhibition study, may be nonlinear, and different inhibition patterns (noncompetitive, competitive, or mixed type) may be observed. Inhibition pattern depends on the cellulase binding constant, enzyme concentration, maximum adsorption of the enzyme (cellulose surface area accessible to the enzyme), the range in which substrate concentration is varied, and beta-glucosidase activity. A limitation of cellulase adsorption by cellulose surface area that may occur at high enzyme/substrate ratio is the main reason for nonlinearity of double-reciprocal plots. Also, the results of calculations showed that material balance by substrate, which is usually neglected by researchers studying cellulase product inhibition, must be taken into account in kinetic analysis even in those cases when the enzyme concentration is rather low. (c) 1992 John Wiley & Sons, Inc. 相似文献