Residual Glucose Concentration Research Articles

Bioethanol production from sugarcane molasses with supplemented nutrients by industrial yeast

Sugarcane molasses, a sugar industry by-product, is being used as a convenient source of carbon for microorganisms to produce bioethanol. The industrial yield of bioethanol derived from Saccharomyces cerevisiae decreases with increasing temperature in the summer season and it is a common issue in the tropical region. It is inevitable to boost the production of bioethanol on an industrial scale to make it commercially profitable. This study has been conducted to analyze and compare the effect of three supplements on boosting alcohol products including thiamine (vitamin B1), pyridoxine (vitamin B6), and D-biotin (vitamin H). Collected molasses were diluted to 20 Brix to make them consumable by yeast, and thiamine, pyridoxine, and biotin were added as 1 mg/l, 1 mg/l, and 0.44 µg/l, respectively. Results depicted that the addition of vitamins impacted very positively on increasing alcohol production, yeast growth, and dry yeast weight where the residual glucose concentration was further decreased. Despite an extended lag phase resulting from higher vitamin doses, there was a significant improvement observed in both alcohol generation and yeast cell growth. This study presents the optimal dosing of supplements in the fermentation broth as a strategy to enhance bioethanol production.

Overexpression of a predicted transketolase gene and disruption of an α-1,3-glucan synthase gene in Aspergillus oryzae DGLA3 strain enhances the yield of free dihomo-γ-linolenic acid.

Free dihomo-γ-linolenic acid (DGLA), a polyunsaturated free fatty acid (FFA), can potentially be used to produce eicosanoid pharmaceuticals, such as prostaglandin E1. Previously, we constructed an Aspergillus oryzae mutant strain, named DGLA3, which produced free DGLA at an increased yield by faaA gene disruption and cooverexpression of one elongase and two desaturase genes. In this study, we achieved a further increase. Since FFA production is increased by enhancing the pentose phosphate pathway, we overexpressed a predicted transketolase gene composing the pathway in DGLA3, which consequently increased the free DGLA yield by 1.9-fold to 403mg/L. Additionally, we disrupted the α-1,3-glucan synthase gene agsB involved in cell-wall biosynthesis, which further increased it by 1.3-fold to 533mg/L. Overall, the yield increased by 2.5-fold. Free DGLA productivity and biomass increased similarly, but residual glucose concentration decreased. Increased hyphal dispersion appeared to cause additional glucose consumption, resulting in an increase in biomass and yield.

Highly Selective Photocatalytic Conversion of Glucose on Holo-Symmetrically Spherical Three-Dimensionally Ordered Macroporous Heterojunction Photonic Crystal

Highly Selective Photocatalytic Conversion of Glucose on Holo-Symmetrically Spherical Three-Dimensionally Ordered Macroporous Heterojunction Photonic Crystal

A hydrotrope pretreatment for stabilized lignin extraction and high titer ethanol production

The biomass pretreatment strategies using organic acids facilitate lignin removal and enhance the enzymatic digestion of cellulose. However, lignin always suffers a severe and irreversible condensation. The newly generated C–C bonds dramatically affect its further upgrading. In this study, we used a recyclable hydrotrope (p-Toluenessulfonic acid, p-TsOH) to dissolve lignin under mild condition and stabilized lignin with a quenching agent (formaldehyde, FA) during extraction, achieving both value-added lignin extraction and efficient enzymatic saccharification of cellulose. Approximately 63.7% of lignin was dissolved by 80% (wt. %) p-TsOH with 1.5% FA addition at 80 °C, 30 min. The obtained lignin was characterized by FTIR spectroscopy, TGA, 2D HSQC NMR spectroscopy, and GPC. The results indicated that the extracted lignin exhibited excellent properties, such as light color, a low molecular weight (Mw, 5371 g/mol), and a narrow polydispersity (Mw/Mn, 1.63). The pretreated substrate was converted to ethanol via a quasi-simultaneous saccharification and fermentation process (Q-SSF). After fermentation of 60 h, the ethanol concentration reached 38.7 ± 3.3 g/L which was equivalent to a theoretical ethanol yield of 82.9 ± 2.2% based on the glucan content, while the residual glucose concentration was only 4.69 ± 1.4 g/L. In short, this pretreatment strategy protected lignin to form new C–C linkages and improved the enzymatic saccharification of glucan for high-titer ethanol production.Graphical

Effect of combination of residual glucose concentration and subsequent increment by temporal glucose feeding on oscillation of clock gene Per2 expression.

With the aim of regulating clock gene expression to control cell activities in cell processing engineering, the effect of the combination of residual glucose concentration and subsequent increment by temporal glucose feeding on the oscillation of the expression of clock gene Per2 was investigated employing rat Mesenchymal stem cell (MSC)-like cells having Per2 promoter gene with a destabilized luciferase gene (Per2-dLuc). Two experiments with several initial glucose concentrations and different times of cultures (2 and 5days) before temporal glucose feeding (0.9g/L) were employed to realize various concentrations of residual glucose in the medium before the feeding. In these experiments, the lower residual glucose concentrations (0.002-0.02g/L) before temporal glucose feeding tended to induce the larger amplitude of oscillation of Per2 expression than the higher ones (0.55-0.74g/L). When the residual glucose concentration before glucose feeding was low (0.014-0.038g/L), the higher temporal glucose concentration (0.23-0.9g/L) feeding tended to induce the larger amplitude of oscillation of Per2 expression than the lower ones (0.012-0.023g/L). Taken together, we found that the amplitude of oscillation of the expression of clock gene Per2 could be controlled by the combination of residual glucose concentration and glucose concentration of subsequent temporal feeding.

Accelerostat study in conventional and microfluidic bioreactors to assess the key role of residual glucose in the dimorphic transition of Yarrowia lipolytica in response to environmental stimuli

Yarrowia lipolytica, with a diverse array of biotechnological applications, is able to grow as ovoid yeasts or filamentous hyphae depending on environmental conditions. This study has explored the relationship between residual glucose levels and dimorphism in Y. lipolytica. Under pH stress conditions, the morphological and physiological characteristics of the yeast were examined during well-controlled accelerostat cultures using both a 1 L-laboratory scale and a 1 mL-microfluidic bioreactor. The accelerostat mode, via a smooth increase of dilution rate (D), enabled the cell growth rate to increase gradually up to the cell wash-out (D ≥μmax of the strain), which was accompanied by a progressive increase in residual glucose concentration. The results showed that Y. lipolytica maintained an ovoid morphology when residual glucose concentration was below a threshold value of around 0.35−0.37 mg L−1. Transitions towards more elongated forms were triggered at this threshold and progressively intensified with the increase in residual glucose levels. The effect of cAMP on the dimorphic transition was assessed by the exogenous addition of cAMP and the quantification of its intracellular levels during the accelerostat. cAMP has been reported to be an important mediator of environmental stimuli that inhibit filamentous growth in Y. lipolytica by activating the cAMP-PKA regulatory pathway. It was confirmed that the exogenous addition of cAMP inhibited the mycelial morphology of Y. lipolytica, even with glucose concentrations exceeding the threshold level. The results suggest that dimorphic responses in Y. lipolytica are regulated by sugar signaling pathways, most likely via the cAMP-PKA dependent pathway.

Using a recyclable acid hydrotrope and subsequent short-term ultrasonic pretreatment to facilitate high-value lignin extraction and high-titer ethanol production

Pretreatment to enhance the enzymatic digestibility of cellulose usually alters the structure of lignin, resulting in subsequent inferior depolymerization and utilization. Herein, a physicochemical pretreatment strategy, specifically, using a recyclable acid hydrotrope (p-toluenesulfonic acid, p-TsOH) followed by 10 s of ultrasonic treatment, was developed to facilitate high-value lignin extraction from lignocellulosic biomass and improve enzymatic hydrolysis for high-titer ethanol production. The wood material (poplar) was first treated with the recyclable p-TsOH aqueous solution under mild conditions (C80T80t15) to extract the lignin. The obtained lignin exhibited excellent properties, including a high hydroxyl (OH) content (4.19 and 4.07 mmol/g of aliphatic and phenolic OH, respectively), abundant β-O-4 aryl ether linkages (60%), a low Mw (3357 ± 121 g/mol), and a narrow polydispersity (2.28, Mw/Mn), according to the results from FTIR spectroscopy, TGA, 31P NMR spectroscopy, 2D-HSQC NMR spectroscopy, and GPC. The pretreated substrates were then subjected to 10 s of ultrasonication to improve the enzymatic saccharification and finally afford ethanol by quasi-simultaneous enzymatic saccharification and fermentation (Q-SSF). The highest ethanol concentration (40.08 ± 3 g/L) was obtained after 60 h of fermentation, and the residual glucose concentration was only 4.22 ± 1 g/L; this experimental ethanol yield was equivalent to the theoretical ethanol yield of 81.87 ± 4% based on the glucan content. In short, this pretreatment method simultaneously enhanced the accessibility of cellulose to enzymatic hydrolysis and provided high-value lignin.

Two-Stage Semi-Continuous 2-Keto-Gluconic Acid (2KGA) Production by Pseudomonas plecoglossicida JUIM01 From Rice Starch Hydrolyzate

A two-stage semi-continuous strategy for producing 2-keto-gluconic acid (2KGA) by Pseudomonas plecoglossicida JUIM01 from rice starch hydrolyzate (RSH) has been developed. The initial glucose concentration (140 g/L) was selected for first-stage fermentation due to its highest 2KGA productivity of 7.58 g/(L⋅h), cell weight of 3.91 g/L, and residual glucose concentration of 25.00 g/L. Followed by removing 70.0% (v/v) of the first-stage broth and feeding 400.0 g/L of glucose to the second-stage fermentor, a total of 50680.0 g glucose was consumed, and 50005.20 g 2KGA was obtained with a yield of 0.9867 g/g by P. plecoglossicida JUIM01 after a 3-cycle two-stage semi-continuous fermentation. Our results indicated that the developed two-stage semi-continuous fermentation could be industrially applied due to its high 2KGA concentration, 2KGA yield and operation efficiency.

Application of Stable Isotope Tracing to Elucidate Metabolic Dynamics During Yarrowia lipolytica α-Ionone Fermentation.

SummaryTargeted metabolite analysis in combination with 13C-tracing is a convenient strategy to determine pathway activity in biological systems; however, metabolite analysis is limited by challenges in separating and detecting pathway intermediates with current chromatographic methods. Here, a hydrophilic interaction chromatography tandem mass spectrometry approach was developed for improved metabolite separation, isotopologue analysis, and quantification. The physiological responses of a Yarrowia lipolytica strain engineered to produce ∼400 mg/L α-ionone and temporal changes in metabolism were quantified (e.g., mevalonate secretion, then uptake) indicating bottleneck shifts in the engineered pathway over the course of fermentation. Dynamic labeling results indicated limited tricarboxylic acid cycle label incorporation and, combined with a measurable ATP shortage during the high ionone production phase, suggested that electron transport and oxidative phosphorylation may limit energy supply and strain performance. The results provide insights into terpenoid pathway metabolic dynamics of non-model yeasts and offer guidelines for sensor development and modular engineering.

Corynebacterium glutamicum, a natural overproducer of succinic acid?

Corynebacterium glutamicum is well known as an important industrial amino acid producer. For a few years, its ability to produce organic acids, under micro‐aerobic or anaerobic conditions was demonstrated. This study is focused on the identification of the culture parameters influencing the organic acids production and, in particular, the succinate production, by this bacterium. Corynebacterium glutamicum 2262, used throughout this study, was a wild‐type strain, which was not genetically designed for the production of succinate. The oxygenation level and the residual glucose concentration appeared as two critical parameters for the organic acids production. The maximal succinate concentration (4.9 g L−1) corresponded to the lower kLa value of 5 h−1. Above 5 h−1, a transient accumulation of the succinate was observed. Interestingly, the stop in the succinate production was concomitant with a lower threshold glucose concentration of 9 g L−1. Taking into account this threshold, a fed‐batch culture was performed to optimize the succinate production with C. glutamicum 2262. The results showed that this wild‐type strain was able to produce 93.6 g L−1 of succinate, which is one of the highest concentration reported in the literature.

B-Cell Receptor Signaling Drives Glycolysis in Chronic Lymphocytic Leukemia Cells

B-Cell Receptor Signaling Drives Glycolysis in Chronic Lymphocytic Leukemia Cells

Engineering of Halomonas bluephagenesis for low cost production of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) from glucose

Poly(3-hydroxybutyrate-co−4-hydroxybutyrate) [P(3HB-co−4HB)] is one of the most promising biomaterials expected to be used in a wide range of scenarios. However, its large-scale production is still hindered by the high cost. Here we report the engineering of Halomonas bluephagenesis as a low-cost platform for non-sterile and continuous fermentative production of P(3HB-co−4HB) from glucose. Two interrelated 4-hydroxybutyrate (4HB) biosynthesis pathways were constructed to guarantee 4HB monomer supply for P(3HB-co−4HB) synthesis by working in concert with 3-hydroxybutyrate (3HB) pathway. Interestingly, only 0.17 mol% 4HB in the copolymer was obtained during shake flask studies. Pathway debugging using structurally related carbon source located the failure as insufficient 4HB accumulation. Further whole genome sequencing and comparative genomic analysis identified multiple orthologs of succinate semialdehyde dehydrogenase (gabD) that may compete with 4HB synthesis flux in H. bluephagenesis. Accordingly, combinatory gene-knockout strains were constructed and characterized, through which the molar fraction of 4HB was increased by 24-fold in shake flask studies. The best-performing strain was grown on glucose as the single carbon source for 60 h under non-sterile conditions in a 7-L bioreactor, reaching 26.3 g/L of dry cell mass containing 60.5% P(3HB-co−17.04 mol%4HB). Besides, 4HB molar fraction in the copolymer can be tuned from 13 mol% to 25 mol% by controlling the residual glucose concentration in the cultures. This is the first study to achieve the production of P(3HB-co−4HB) from only glucose using Halomonas.

Enhancement of L-Threonine Production by Controlling Sequential Carbon-Nitrogen Ratios during Fermentation.

Controlling the residual glucose concentration is important for improving productivity in L-threonine fermentation. In this study, we developed a procedure to automatically control the feeding quantity of glucose solution as a function of ammonia-water consumption rate. The feeding ratio (RC/N) of glucose and ammonia water was predetermined via a stoichiometric approach, on the basis of glucose-ammonia water consumption rates. In a 5-L fermenter, 102 g/l L-threonine was obtained using our glucose-ammonia water combined feeding strategy, which was then successfully applied in a 500-L fermenter (89 g/l). Therefore, we conclude that an automatic combination feeding strategy is suitable for improving L-threonine production.

Power input effects on degeneration in prolonged penicillin chemostat cultures: A systems analysis at flux, residual glucose, metabolite, and transcript levels.

In the present work, by performing chemostat experiments at 400 and 600 RPM, two typical power inputs representative of industrial penicillin fermentation (P/V, 1.00 kW/m3 in more remote zones and 3.83 kW/m3 in the vicinity of the impellers, respectively) were scaled-down to bench-scale bioreactors. It was found that at 400 RPM applied in prolonged glucose-limited chemostat cultures, the previously reported degeneration of penicillin production using an industrial Penicillium chrysogenum strain was virtually absent. To investigate this, the cellular response was studied at flux (stoichiometry), residual glucose, intracellular metabolite and transcript levels. At 600 RPM, 20% more cell lysis was observed and the increased degeneration of penicillin production was accompanied by a 22% larger ATP gap and an unexpected 20-fold decrease in the residual glucose concentration (Cs,out ). At the same time, the biomass specific glucose consumption rate (qs ) did not change but the intracellular glucose concentration was about sixfold higher, which indicates a change to a higher affinity glucose transporter at 600 RPM. In addition, power input differences cause differences in the diffusion rates of glucose and the calculated Batchelor diffusion length scale suggests the presence of a glucose diffusion layer at the glucose transporting parts of the hyphae, which was further substantiated by a simple proposed glucose diffusion-uptake model. By analysis of calculated mass action ratios (MARs) and energy consumption, it indicated that at 600 RPM glucose sensing and signal transduction in response to the low Cs,out appear to trigger a gluconeogenic type of metabolic flux rearrangement, a futile cycle through the pentose phosphate pathway (PPP) and a declining redox state of the cytosol. In support of the change in glucose transport and degeneration of penicillin production at 600 RPM, the transcript levels of the putative high-affinity glucose/hexose transporter genes Pc12g02880 and Pc06g01340 increased 3.5- and 3.3-fold, respectively, and those of the pcbC gene encoding isopenicillin N-synthetase (IPNS) were more than twofold lower in the time range of 100-200 hr of the chemostat cultures. Summarizing, changes at power input have unexpected effects on degeneration and glucose transport, and result in significant metabolic rearrangements. These findings are relevant for the industrial production of penicillin, and other fermentations with filamentous microorganisms.

Nonlinear robust adaptive control strategies for a lactic fermentation process

AbstractBACKGROUNDThis work addresses the design of robust adaptive control strategies for a lactic fermentation process carried out inside a continuous stirred tank reactor (CSTR). This bioprocess is widely used in bioindustry for lactic acid production, and it is characterized by strong nonlinearities and uncertainties. Under the realistic assumption that the reaction kinetics and the influent flow rates are unknown and time‐varying, but lower and upper bounds of the uncertainties are known, two innovative robust adaptive control structures are proposed.RESULTSThe control strategies are designed by combining a linearizing control law with two novel parameter estimators able to estimate the unknown reaction rates. The first strategy uses a modified observer based estimator and the second one utilizes an interval parameter estimator. The control objective is to adjust the plant load so as to convert the glucose into lactic acid via fermentation, which is directly correlated with the economic aspects of lactic acid production. Numerical simulations are performed in order to validate the proposed solution.CONCLUSIONBy using the proposed control strategies the process is maintained at certain operating points that correspond to a maximum lactic production rate and a minimal residual glucose concentration. The simulations performed by considering various uncertainties and noisy measurement data show that the proposed novel robust adaptive controllers are suitable to control this kind of fermentation processes. © 2017 Society of Chemical Industry

Bioremediation of Hexavalent Chromium in Potassium Dichromate Solution by Botrytis aclada fres and Chrysonilia sitophila

Bioremediation of hexavalent chromium, Cr(VI) by Botrytis aclada fres and Chrysonilia sitophila was studied. The organisms were isolated from decaying onion bulb and apple fruit respectively, purified in Potato Dextrose Agar, and grown for 144 hours in solutions of potassium dichromate of concentrations ranging from 5-20 mg/l at 40 0 C. Effective reduction of Cr(VI) was observed at 5-20 mg/l compared to 25 mg/l dichromate treatments in both organisms. The results showed significant decrease (P < 0.05) in biomass concentration in the two fungi used with increasing concentration of the dichromate treatment (5-25 mg/l). Significant increase (P < 0.05) in residual glucose concentration was also observed in the culture media with increase in concentration of the dichromate treatment. However, at 20 mg/l dichromate treatment, Cr(IV) concentration, 1.36 ± 0.02 and 1.71 ± 0.03 (P < 0.05) were revealed in the culture media of B. aclada fres and C. sitophila respectively. Also, 0.71 ± 0.03 and 0.94 ± 0.03 Cr(IV) concentration (P < 0.05) were observed in the fungal mycelia at 20 mg/l dichromate treatment in B. aclada fres and C. sitophila respectively. After 144 hours of growth, Cr(VI) reduction of 89.65% in B. aclada fres and 86.75% in C. sitophila at 20 mg/l dichromate treatment were revealed. This investigation suggests that the two fungi adopted a process of reduction to tolerate the toxicity of hexavalent chromium. The results indicate the potentials of the fungi in bioremediation particularly in the treatment of waste water containing hexavalent chromium.

Succinic Acid Production by Actinobacillus Succinogenes in Chemostat and Biofilm Cultures

Previously published results from a novel, homogeneously distributed shear, tubular fermenter used to study continuous chemostat (high shear) and biofilm (low shear) fermentations (Brink and Nicol, 2014a), were compared to results obtained in the same reactor at intermediate shear conditions as well as batch (biofilm) fermentations of Actinobacillus succinogenes.It was found that the steady-state volumetric production rates increased by nearly an order of magnitude (1.8 g.L-1.h-1 vs 15–17 g.L-1.h-1) as the shear was reduced from the chemostat (1.83 m.s-1) to the lower shear biofilm conditions. The biofilm results indicated similar volumetric production rates for the different shear conditions, while the measured extracellular polymeric substances (EPS) in the biofilm exhibited a significant shear dependence; EPS fractions of 0.50 ± 0.05 g.g-1 vs. 0.16 ± 0.02 g.g-1 for the low and intermediate shear conditions respectively. The cell-based biofilm production rates were shown to be dependent on shear conditions at succinic acid titres less than the growth-maintenance boundary (10 g.L-1), with a reduction in cellular production rate associated with an increase in shear. Under maintenance conditions the cell-based production rates appeared independent of the shear conditions in the fermenter, with the cell-based production rates decreasing with increasing succinic acid titres. The industrial implications are that for succinic acid titres in excess of 10 g.L-1, the same mass of biomass under intermediate shear conditions should exhibit a greater volumetric production rate due to the higher fraction of cells as opposed to EPS.The initial values for the batch cell-based succinic acid production rates corresponded to the steady-state values for biofilms grown under the same continuous conditions. However, during transient operation the production rates exceeded the steady-state values; a lag in the product inhibition response was observed. The transient production rates eventually ceased at succinic acid titres in excess of approximately 60–72 g.L-1; a residual glucose concentration of 20 g.L-1 was measured at the highest succinic acid titre (72 g.L-1), indicating product related inhibition as opposed to substrate depletion. The transient results indicate that a larger average cell- based production rate can be obtained during transient operation when compared to the steady fermentation conditions due to a lag in the succinic acid inhibition during transient operation.

Growth-rate dependency of de novo resveratrol production in chemostat cultures of an engineered Saccharomyces cerevisiae strain.

IntroductionSaccharomyces cerevisiae has become a popular host for production of non-native compounds. The metabolic pathways involved generally require a net input of energy. To maximize the ATP yield on sugar in S. cerevisiae, industrial cultivation is typically performed in aerobic, sugar-limited fed-batch reactors which, due to constraints in oxygen transfer and cooling capacities, have to be operated at low specific growth rates. Because intracellular levels of key metabolites are growth-rate dependent, slow growth can significantly affect biomass-specific productivity. Using an engineered Saccharomyces cerevisiae strain expressing a heterologous pathway for resveratrol production as a model energy-requiring product, the impact of specific growth rate on yeast physiology and productivity was investigated in aerobic, glucose-limited chemostat cultures.ResultsStoichiometric analysis revealed that de novo resveratrol production from glucose requires 13 moles of ATP per mole of produced resveratrol. The biomass-specific production rate of resveratrol showed a strong positive correlation with the specific growth rate. At low growth rates a substantial fraction of the carbon source was invested in cellular maintenance-energy requirements (e.g. 27 % at 0.03 h−1). This distribution of resources was unaffected by resveratrol production. Formation of the by-products coumaric, phloretic and cinnamic acid had no detectable effect on maintenance energy requirement and yeast physiology in chemostat. Expression of the heterologous pathway led to marked differences in transcript levels in the resveratrol-producing strain, including increased expression levels of genes involved in pathways for precursor supply (e.g. ARO7 and ARO9 involved in phenylalanine biosynthesis). The observed strong differential expression of many glucose-responsive genes in the resveratrol producer as compared to a congenic reference strain could be explained from higher residual glucose concentrations and higher relative growth rates in cultures of the resveratrol producer.ConclusionsDe novo resveratrol production by engineered S. cerevisiae is an energy demanding process. Resveratrol production by an engineered strain exhibited a strong correlation with specific growth rate. Since industrial production in fed-batch reactors typically involves low specific growth rates, this study emphasizes the need for uncoupling growth and product formation via energy-requiring pathways.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-015-0321-6) contains supplementary material, which is available to authorized users.

Culturing Drosophila melanogaster (S2) in a chemostat.

Insect cells are used for the expression of complex proteins in products such as vaccines and biopharmaceuticals. Physiology of a Drosophila melanogaster (lineage S2), transfected to stably express rabies virus glycoprotein (RVGP), was studied in batch culture and in a chemostat with serum-free medium. In batch mode, the system reached 3×10(7)cellsmL(-1) with specific growth rate of 1.5d(-1) with RVGP at 2.50µgL(-1). When operated continuously, three well-defined steady states were achieved at dilution rates (D) of 0.8, 0.5 and 0.2d(-1). The residual glucose and glutamine concentrations and the cell yields on glucose and glutamine decreased at lower D. High values of substrate consumption for maintenance may explain this variation in yields. The results indicated that glucose is not the limiting substrate of this process.

Production of Bioactive Substances in Fed-batch and Semi- continuous Culture by Pleurotus Ostreatus

Therapeutic properties of Pleurotus genus are associated with the polysaccharides present in the mycelium cell wall and culture broth of submerged cultures. The production of extracellular polysaccharides (EPS) by Pleurotus ostreatus using fed-batch and semi-continuous culture with 50 and 75% medium replacement was investigated. The assays were performed in 4L bioreactor with 40 g L-1 initial glucose concentration. Medium replacements were performed when residual glucose concentration reached 20 - 25 g L-1.The highest fungal biomass productivity was obtained in semi-continuous culture with 75 % medium replacement (61.02 mg L-1 h-1) followed by fed-batch (30.00 mg L-1 h-1) and 50 % medium replacement (23.4 mg L-1 h-1). However, the highest global EPS productivity (6.06 mg L-1 h-1) was obtained in semi- continuous culture with 50 % medium replacement. 75 % medium replacement and fed-batch led to EPS productivities of 4.03 and 3.78 mg L-1 h-1, respectively.The highest EPS productivity was promoted by semi-continuous culture with 50 % medium replacement, in the second batch (9 mg L-1 h-1). This process can be improved in order to maintain this high productivity value in further batches. Fed-batch culture under tested conditions was not effective for EPS production byostreatus.