Initial Yeast Extract Concentration Research Articles

Bioreactor study of the metabolic repertoire and morphology of actinomycete Streptomyces rimosus ATCC 10970 under various initial concentrations of carbon and nitrogen sources

This work aims at investigating the influence of the initial concentrations of carbon (glucose) and organic nitrogen (yeast extract) sources on Streptomyces rimosus ATCC10970 secondary metabolism in the stirred tank bioreactors. Additionally, glucose utilisation, biomass formation, pH, redox potential and dissolved oxygen levels, and the morphological development of S. rimosus pseudomycelium were studied. Eighteen secondary metabolites were detected by mass spectrometry and identified with the use of the authentic standard, or putatively with the use of literature and database of secondary metabolites. Varied initial yeast extract concentration acted much stronger on the formation of secondary metabolites than glucose did. For example, oxytetracycline was not biosynthesised at high yeast extract concentration while the formation of three other metabolites was enhanced under these conditions. In the case of glucose its increasing initial concentration led to higher secondary metabolite levels with the exception of an unnamed angucycline. High initial yeast extract concentration also drastically changed S. rimosus pseudomycelial morphology from the pelleted to the dispersed one. Ultimately, the cultivation media with the varied initial levels of carbon and nitrogen sources were proved to have the marked effect on S. rimosus secondary metabolism and to be the simplest way to either induce or block the formation of the selected secondary metabolites.

Development of natural seawater-based continuous biohydrogen production process using the hyperthermophilic archaeon Thermococcus onnurineus NA1

Previously, we reported that the hyperthermophilic archaeon, Thermococcus onnurineus NA1 could produce hydrogen from various resources including carbon monoxide (CO) with high productivity. In this study, a high-performance and cost-effective fermentation process was developed as a prerequisite for the industrial implementation of H2 production from CO using the strain. Firstly, an economical medium was formulated on the basis of natural seawater. Cysteine as a reducing agent was found to be an important factor to consider. Secondly, three variables, initial concentration of yeast extract, CO supply rate and agitation rate, were statistically optimized in batch culture by applying a response surface methodology. Notably, biomass productivity of 0.39 g/L/h could be observed and cell density reached 14 optical units at 600 nm, which is exceptionally high among members of the order Thermococcales. Finally, continuous cultures were tested at various dilution rates with new medium formulation and optimized culture conditions. As a result, the steady state of H2 production and cell growth were stably maintained, yielding H2 production rate of 471.5 mmol/L/h at a dilution rate of 0.1 h−1, which is one of the highest values at ambient CO pressure to date. Our study shows that T. onnurineus NA1 has outstanding potential as an economical and high performance industrial strain suitable for long-term processes for CO-dependent H2 production.

Docosahexaenoic acid (DHA) production by Aurantiochytrium limacinum using cassava pulp hydrolysate as an alternative low-cost carbon source

Cost of nutrients is one of the major contributors to the production cost of docosahexaenoic acid (DHA) by thraustochytrids, and this remains the main challenge for economical and sustainable production of DHA. In the present study, cassava pulp (CP) was investigated as an alternative low-cost carbon source for DHA production by Aurantiochytrium limacinum SR21. Cultivation conditions, i.e., salinity level, type of nitrogen source, and concentrations of glucose and nitrogen sources, as well as pH, were optimized for cell growth. CP was enzymatically hydrolyzed, and used as the base medium, supplemented with artificial seawater salts, for DHA production under fed-batch cultivation. A. limacinum grew well at 18 g/L of NaCl (equivalent to 50% salinity level), and initial glucose concentration of 64 g/L, initial yeast extract concentration of 5 g/L, and pH 7.5 were optimum for cell growth. Fed-batch cultivation, with dissolved oxygen (DO) controlled at 10%, using CP-based medium as the carbon source gave a final cell dry mass of 26.3 ± 2.0 g/L, with 15.5 ± 0.1 g/L of lipid. DHA content in the lipid was 37.4 ± 1.5%, equivalent to 5.8 ± 0.3 g/L, and DHA productivity was 960 mg/(L·d). Medium-based economic analysis showed that an economic yield (EY) of this process was 0.86, which was higher than the 0.81 obtained using glucose as the substrate, assuming the same process and conditions. Overall, the results reveal that CP is a highly feasible feedstock for DHA production by A. limacinum SR21.

PRODUCTION OF 2,3-BUTANEDIOL BY KLEBSIELLA PNEUMONIAE FROM ENZYMATIC HYDROLYZATE OF SUGARCANE BAGASSE

Fermentation conditions for 2,3-butanediol (2,3-BD) production by Klebsiella pneumoniae CGMCC1.9131 were optimized statistically in shake flasks. Four significant factors including the initial concentrations of yeast extract, glucose, K2HPO4, and (NH4)2SO4 were optimized by Response Surface Methodology (RSM). To further improve the yield of 2,3-BD, EDTA Na2 was added to the medium. After optimization, the yield of 2,3-BD was 0.44 g/g glucose and the final concentration was 26.20 g/L when initial glucose concentration was 60 g/L. The enzymatic hydrolyzate of pretreated sugarcane bagasse by alkali-peracetic acid (PAA) and dilute acid were further used as feedstock to produce 2,3-BD under the optimized conditions, and the yields of 2,3-BD were 0.36 and 0.43 g/g consumed sugars, respectively. The experimental results indicated that the enzymatic hydrolyzate could be well converted to 2,3-BD.

Optimization of a biotransformation process to produce 4-(2,3,5,6-tetramethylpyrazine-1)-4′-demethylepipodophyllotoxin

The developed tandem biotransformation process for the directional biosynthesis of a designed compound 4-(2,3,5,6-tetramethylpyrazine-1)-4′-demethylepipodophyllotoxin (4-TMP-DMEP) by Alternaria alternata S-f6 was systematically optimized. 28°C of culture temperature and 120rpm of rotary shaker speed were suitable for the accumulation of 4-TMP-DMEP. The production (i.e., 11.1±1.4mg/L) of 4-TMP-DMEP was remarkably improved by using an initial yeast extract concentration of 2.5g/L. 2.0g/L of Span 80 was beneficial for the 4-TMP-DMEP production (i.e., 25.0±1.5mg/L). Furthermore, the 4-TMP-DMEP production was remarkably improved by one pulse feeding of 50mg/L of DMEP on day 6 and two pulse feedings of 40mg/L of TMP on days 8 and 14 when its residual level was below 50mg/L and 10mg/L, respectively. The 4-TMP-DMEP production of 45.1±1.6mg/L was obtained in the fed-batch biotransformation process, which was enhanced by 726% and 256%, comparing to that (i.e., 5.4±0.4mg/L and 0.9mg/L/day) obtained in the batch biotransformation before optimization.

Production and characterization of ectoine by Marinococcus sp. ECT1 isolated from a high-salinity environment

A halophilic bacterium isolated from a salt environment in southern Taiwan was identified as a Marinococcus sp. ECT1. This bacterium could synthesize and accumulate intracellular ectoine as a compatible solute capable of resisting osmotic stress in a hyper-osmotic environment. This study also developed a semi-synthesized medium (YAMS medium), capable of facilitating the growth of this Marinococcus sp. ECT1 with 600 mg/L crude ectoine production. Moreover, Marinococcus sp. ECT1 was grown on YAMS medium containing different initial yeast extract concentrations (C(YE)) (0 to 60 g/L) to demonstrate how C(YE) affects crude ectoine production. While the maximum cell concentration was increased by 23-fold when the C(YE) was 40 g/L, the maximum crude ectoine production reached 2.5 g/L when C(YE) was 40 g/L. In addition to demonstrating the success of the fermentation strategy of ectoine in increasing the production and production yield, experimental results further demonstrated that the fermentation medium of ectoine is highly promising for commercialization. Furthermore, the molecular weight and chemical structure of ectoine were identified and characterized by FAB-MS and (1)H-NMR.

The properties of Kluyveromyces lactis for the production of D-arabitol from lactose

Production of D-arabitol from lactose by Kluyveromyces lactis NBRC 1903 was investigated to make a solution for utilization of whey. It turned out that initial concentration of yeast extract, working volume and initial cell mass concentration are important factors in D-arabitol production from lactose by this strain. It was indicated that higher aerobic condition was preferable for D-arabitol production from lactose by K. lactis. Highest D-arabitol concentration of 13.5 g L -1 was obtained at 96 h cultivation with 0.002 g L -1 of initial cell mass concentration, 40 g L -1 of initial yeast extract concentration and 2 mL of working volume. Key words : D-Arabitol, lactose, Kluyveromyces lactis, ethanol.

Response surface modeling the significance of nitrogen source on the cell growth and Tuber polysaccharides production by submerged cultivation of Chinese truffle Tuber sinense

Truffles are hypogeous ascomycetes and ectomycorrhizal fungi with unique organoleptic properties. Effects of nitrogen source and its concentration were studied during the submerged fermentation of Chinese truffle Tuber sinense. Yeast extract was identified to be the most favorable for the cell growth, and the next was peptone. The maximal dry cell weight of 19.53 ± 0.13 g/L obtained at an initial yeast extract concentration of 25 g/L was higher by 40.9% compared to that at 10 g/L. Within the range of initial peptone concentration (i.e., 10, 20, 30 and 40 g/L) as investigated, the maximal biomass and the production of extracellular polysaccharide (EPS) were obtained at 30 g/L, while 20 g/L was favorable for the production of intracellular polysaccharide (IPS). A mathematical model, which was constructed by response surface methodology combination with Box-Behnken design (BBD), was applied to study the synergic effect of glucose, yeast extract and peptone. According to the model prediction, the optimal initial concentration of glucose, yeast extract and peptone was 60, 30 and 10 g/L, respectively. The validation experiment showed the experimental values agreed with the predicted values well. The highest biomass (i.e., 23.94 ± 0.49 g/L), the production of EPS (i.e., 1.59 ± 0.06 g/L) and IPS (i.e., 1.48 ± 0.26 g/L) were obtained under the predicted optimal conditions, which were higher by 22.6%, 42.0% and 16.5% compared with the best results of one-variable-at-a-time experiments, respectively.

Simultaneous biosynthesis of (+)-geodin by a lovastatin-producing fungus Aspergillus terreus

The simultaneous biosynthesis of lovastatin (mevinolinic acid) and (+)-geodin by Aspergillus terreus ATCC 20542 with regard to the medium composition, i.e. the concentrations of carbon and nitrogen source, was described in this paper. A. terreus is a lovastatin producer but the formation of lovastatin was accompanied by the significant amounts of (+)-geodin, when the elevated concentration of carbon source (lactose) was still present in the medium in the idiophase and nitrogen source (yeast extract) was deficient. It was observed for runs, in which the higher (above 20 g l −1) initial lactose concentration was applied or when the nitrogen deficiency led to the decrease of biomass content in the system. In contrast to lovastatin, there was not optimum initial concentration of yeast extract, as its lowest tested initial concentration (2 g l −1) led to the highest (+)-geodin volumetric formation rates and final yield. What is more, even higher final (+)-geodin concentrations were achieved at elevated initial lactose concentration (40 g l −1) and in the lactose-fed fed-batch run. In the fed-batch run lovastatin concentration increased significantly too, as this metabolite formation is also carbon source dependent. Finally, (+)-geodin occurred to be a metabolite, whose formation, in contrast to lovastatin, is non-growth associated.

Application of fractional factorial design to levan production by Zymomonas mobilis

Levan is a non-toxic, biologically active, extra cellular polysaccharide composed solely by fructose units. Optimization of levan production by Zymomonas mobilis strain ZAG-12 employing a 24-1 fractional factorial design was performed to analyze the influence of the temperature (20, 25 e 30oC) agitation (50, 75 e 100 rpm), and the initial concentrations of both sucrose (150, 200 e 250 g.L-1) and yeast extract (2.0, 3.5 e 5.0g.L-1) on final levan concentration. Aerobic fermentation was performed batchwise in 500mL Pyrex flasks for 72 hours. Biomass, ethanol, levan and sucrose were determined at beginning and also at end of the fermentations. The experiments showed that the final levan concentration depended on initial sucrose concentration, temperature and agitation velocity and that the initial concentration of yeast extract did not influence levan production. However, when the production of ethanol and biomass were considered, it became evident that yeast extract was a significant variable. The best conditions for levan production occurred at 100 rpm agitation, 20oC and 250g.L-1 of initial sucrose resulting in 14.67g.L-1 of levan.

Kinetics of Glycerol Biotransformation to Dihydroxyacetone by Immobilized Gluconobacter oxydans and Effect of Reaction Conditions

Biotransformation of glycerol to 1,3-dihydroxyacetone was carried out in an isothermal isochoric batch reactor with Gluconobacter oxydans immobilized in poly(vinyl alcohol) gel capsules. The reaction course was described with a three-step kinetic model. Two reaction schemes were proposed and compared with 8 kinetic experiments at 25 °C. The experimental dependences of glycerol and dihydroxyacetone concentrations on reaction time were simulated very well by the autocatalytic model. The effects of reaction temperature and initial concentrations of yeast extract and glycerol were studied. Temperature 25-30 °C, initial yeast extract concentration 2-4 g l-1 and initial glycerol concentration 20-50 g l-1 were found as optimal. The determined rate constants can be used to advantage for industrial production of dihydroxyacetone from glycerol.

Biological treatment of wastewater discharged from biodiesel fuel production plant with alkali-catalyzed transesterification

The biological treatment of wastewater discharged from a biodiesel fuel (BDF) production plant conducting alkali catalysis transesterification was investigated. BDF wastewater has a high pH and high hexane-extracted oil and low nitrogen concentrations, and inhibits the growth of microorganisms. The biological treatment of BDF wastewater is difficult because the composition of such wastewater is not suitable for microbial growth. To apply the microbiological treatment of BDF wastewater using an oil degradable yeast, Rhodotorula mucilaginosa, the pH was adjusted to 6.8 and several nutrients such as a nitrogen source (ammonium sulfate, ammonium chloride or urea), yeast extract, KH2PO4 and MgSO4.7H2O were added to the wastewater. The optimal initial concentration of yeast extract was 1 g/l and the optimal C/N ratio was between 17 and 68 when using urea as a nitrogen source. A growth inhibitor was also present in the BDF wastewater, and this growth inhibitor could be detected by measuring the solid content in an aqueous phase after the hexane extraction of the wastewater. Microorganisms could not grow at solid contents higher than 2.14 g/l in the wastewater. To avoid the growth inhibition, the BDF wastewater was diluted with the same volume of water. Oil degradation in the diluted BDF wastewater was observed and the best result was obtained under the determined optimal conditions. This treatment system is simple because no controllers, except for a temperature, are necessary. These results suggest that the biological treatment system developed for BDF wastewater is useful for small-scale BDF production plants.

Effects of process parameters on heterologous protein production in Aspergillus niger fermentation

AbstractFilamentous fungi such as Aspergillus niger are attractive hosts for recombinant DNA technology because of their ability to secrete bioactive proteins with post‐translational processing such as glycosylation. Foreign genes can be incorporated into the chromosomes of the filamentous fungi, providing superior long‐term genetic stability. However, heterologous protein production is often severely hampered by fungal proteases. In this work, a recombinant Aspergillus niger strain AB4.1[pgpdAGLAGFP]#11 which carries a glucoamylase (GLA)‐green fluorescent protein (GFP) fusion gene was selected as a model system to study the effects of bioprocess parameters—agitation intensity, initial glucose concentration, initial yeast extract concentration, and dissolved oxygen tension (DO)—on extracellular protease inhibition and heterologous protein production. Based on previous experimental experience and results, a 24–1 fractional factorial design was applied to the experiments. Each parameter was tested at two levels. It was found that agitation affected the GFP production most significantly. Higher agitation rate resulted in higher GFP production. Protease activity was most influenced by initial glucose concentration and DO. Fungal morphology was also affected by these parameters. The effects of these parameters on pellet size and pellet porosity are discussed. Copyright © 2003 Society of Chemical Industry

Analysis of growth and production coupling for batch cultures of Lactobacillus helveticus with the help of an unstructured model

An unstructured model has been developed by assuming a sigmoidal variation with time of specific growth rate and introducing an additional term in Luedeking and Piret production kinetics. The model fitted growth and production kinetic data. The model was helpful for examining the influence of initial yeast extract concentration on growth and production coupling. In richly supplemented media, the growth associated production mechanism prevailed, while in the case of poor nitrogen supplementation, most lactic acid production was non-growth-associated. Both contributions might be calculated from model parameters; this was especially interesting when the forms of growth and production kinetics did not allow a clear conclusion. The additional term in the production rate expression was a convenient way to characterize ‘usable nitrogen’ concentration in the medium. From the model a clear criterion has been derived for optimizing the nitrogen supplementation from an economic point of view.

Development of a fermentation process for production of a κ-carrageenase from Pseudomonas carrageenovora

The production of κ-carrageenase was studied in Pseudomonas carrageenovora strains NCIMB 302 and 9. The average specific production rate of κ-carrageenase by strain NCIMB 302 on a semidefined yeast extract medium was found to be 15 times as high as in strain 9. A linear relationship was obtained for strain NCIMB 302 in batch fermentation between the κ-carrageenase activity and the initial concentration of yeast extract. A similar linear correlation was also achieved for enzyme production on the κ-carrageenan concentration. κ-Carrageenan as an inducer could not be replaced by a low viscosity, low molecular galactose-containing carbohydrate. Supplying κ-carrageenan by fed-batch addition prolongs the time of enzyme production to a small extent, but the observed enzyme concentration was not increased. At low values, a significant increase in enzyme activity was achieved with increasing casamino acid concentration up to 3.5 g l −1, but the maximum activity decreased on further addition. When casamino acids were supplied as fed-batch, however, the production time was prolonged significantly and the enzyme activity increased 2.6 times up to 84,000 U l −1 (observed) or more than four times up to 136,000 U l −1 estimated as volume-corrected values. Substituting the casamino acids by an equal amount of a single amino acid (glutamic acid), a similar enzyme production was obtained. The highest observed enzyme activity obtained here is 17 times higher than the values reported earlier (or 27 times higher when volume-corrected values are assessed).

Effects of medium components on L-ornithine production byBrevibacterium ketoglutamicum

Effects of yeast extract, and ammonium sulfate were investigated on the production of L-ornithine by an arginine auxotroph.Brevibacterium ketoglutamicum in flask and batch cultures. Yeast extract as an arginine source and ammonium sulfate as an inorganic nitrogen source had significant effects on L-ornithine, production and cell growth. L-ornithine production was repressed by the excessive addition of arginine. Reversion of auxotrophic cells to the wild type was observed when the initial yeast extract concentration was too low. There existed optimum concentrations of yeast extract and ammonium sulfate for L-ornithine production. The effects of yeast extract and ammonium sulfate concentrations on the Leudeking-Piret model parameters were examined to analyze, the relationship between cell growth and L-ornithine production.

Production of xylitol from D‐xylose by candida tropicalis: Optimization of production rate

The effect of culture conditions on xylitol production rate was investigated using Candida tropicalis IFO 0618. From the variance analysis of xylitol production rate, it was found that initial yeast extract concentration was highly significant (99%), while the interaction between D-xylose concentration and aeration rate was significant (95%). These results show the importance of initial yeast extract concentration and of the balance between D-xylose concentration and aeration in the production of xylitol. It was also clearly shown that C. tropicalis needed more yeast extract concentration for efficient xylitol production than for its growth. In order to enhance xylitol production rate, culture conditions were optimized by the Box-Wilson method. In this respect, initial D-xylose concentration, yeast extract concentration, and K(L)a were chosen as the independent factors in 2(3)-factorial experimental design. As the result of experiments, a maximum xylitol production rate of 2.67 g/L . h was obtained when initial D-xylose concentration and yeast extract concentration were 172.0 and 21.0 g/L, respectively, and K(L)a was 451.50 h(-1) by 90% oxygen gas.

Effect of pH and the initial concentration of yeast extract on regulation of dimorphism and exopolysaccharide formation of Aureobasidium pullulans in batch culture

The effect of yeast extract on morphology and exopolysaccharide formation of Aureobasidium pullulans was followed quantitatively in batch cultivations in 2 1 fermenters. When the fungus was grown at controlled pH 6·5 or 3·5 or uncontrolled with initial pH 6·5 in media with glucose (10 gl−1) and surplus of ammonium the formation of yeast-like cells and yeast-like growth were controlled by the initial concentration of yeast extract (varied from 0·4 to 4 g l−1). With sufficient yeast extract added the growth form was filamentous until glucose became exhausted at the onset of stationary phase. Formation of yeast-like cells was a prerequisite of formation of exopolysaccharide, the initiation of which was correlated with the initiation of yeast-like growth. Exopolysaccharide was produced in media as well with a surplus of ammonium as without ammonium.

Modern theories of fermentation, with notes on the morphology and culture of yeasts

The production of κ-carrageenase was studied in Pseudomonas carrageenovora strains NCIMB 302 and 9. The average specific production rate of κ-carrageenase by strain NCIMB 302 on a semidefined yeast extract medium was found to be 15 times as high as in strain 9. A linear relationship was obtained for strain NCIMB 302 in batch fermentation between the κ-carrageenase activity and the initial concentration of yeast extract. A similar linear correlation was also achieved for enzyme production on the κ-carrageenan concentration. κ-Carrageenan as an inducer could not be replaced by a low viscosity, low molecular galactose-containing carbohydrate. Supplying κ-carrageenan by fed-batch addition prolongs the time of enzyme production to a small extent, but the observed enzyme concentration was not increased. At low values, a significant increase in enzyme activity was achieved with increasing casamino acid concentration up to 3.5 g l−1, but the maximum activity decreased on further addition. When casamino acids were supplied as fed-batch, however, the production time was prolonged significantly and the enzyme activity increased 2.6 times up to 84,000 U l−1 (observed) or more than four times up to 136,000 U l−1 estimated as volume-corrected values. Substituting the casamino acids by an equal amount of a single amino acid (glutamic acid), a similar enzyme production was obtained. The highest observed enzyme activity obtained here is 17 times higher than the values reported earlier (or 27 times higher when volume-corrected values are assessed).