Cysteine addition strategy for maximum glutathione production in fed-batch culture of Saccharomyces cerevisiae

An efficient method of growing the protozoon Tetrahymena to high cell densities in a 2-1 bioreactor is described. The first phase of the fermentation is a batch phase with minimum generation times (1.4 h). During the next phase medium is exchanged continuously using a perfusion module based on microporous hollow fibres while cell are retained. Compared to standard batch fermentations of this organism 30- to 40-fold higher cell concentrations and dry weights were achieved routinely. A maximum cell concentration of 2.2 × 10⁷ cells/ml and a dry weight of 54 g/l have been obtained. As estimated from isocitrate dehydrogenase activity in the culture medium, no cell damage occurred even at high agitation rates. In addition, the cells remained viable for several weeks. Temporal limitation of the process was due to a decrease in the perfusion rate caused by blocking of the membranes. By X-ray microprobe analysis calcium phosphate depositions were detected in the pores of the clogged hollow-fibre membranes. However, even a T. pyriformis strain possessing mucocysts, dense core secretory organelles that may lead to early membrane clogging, was cultivated successfully for 3 weeks. Additionally, the consumption of nutrient protein and carbohydrates during fermentation was investigated and the effect of different perfusion rates and of glucose was studied in order to increase the efficieny of the system.Correspondence to: A. Tiedtke     

Production of Extracellular Polysaccharide by Zoogloea ramigera

In batch cultures of Zoogloea ramigera the maximum rate of exopolysaccharide synthesis occurred in a partly growth-linked process. The exopolysaccharide was attached to the cells as a capsule. The capsules were released from the cell walls after 150 h of cultivation, which caused the fermentation broth to be highly viscous. Ultrasonication could be used to release capsular polysaccharide from the microbial cell walls. Treatment performed after 48 to 66 h of cultivation revealed exopolysaccharide concentration and apparent viscosity values in accordance with values of untreated samples withdrawn after 161 h of cultivation. The yield coefficient of exopolysaccharide on the basis of consumed glucose was in the range of 55 to 60% for batch cultivations with an initial glucose concentration of 25 g liter⁻¹. An exopolysaccharide concentration of up to 38 g liter⁻¹ could be attained if glucose, nitrogen, and growth factors were fed into the batch culture. The oxygen consumption rate in batch fermentations reached 25 mmol of O₂ liter⁻¹ h⁻¹ during the exopolysaccharide synthesis phase and then decreased to values below 5 mmol of O₂ liter⁻¹ h⁻¹ during the release phase. The fermentation broth showed pseudoplastic flow behavior, and the polysaccharide was not degraded when growth had ceased.     

Ethanol production from wheat flour by Zymomonas mobilis

Starch from wheat flour was enzymatically hydrolyzed and used for ethanol production by Zymmonas mobilis. The addition of a nitrogen source like ammonium sulfate was sufficient to obtain a complete fermentation of the hdyrolyzed strach. In batch culture a glucose concentration as high as 223 g/l could be fermented (conversion 99.5%) to 105 g/l of ethanol in 70 h with an ethanol yield of 0.47 g/g (92% of theoretical). In continuous culture the use of a flocculent strain and a fermentor with an internal settler resulted (D=1,4 h⁻¹) in a high ethanol productivity of 70.7 g/l·h with: ethanol concentration 49.5 g/l, ethanol yield 0.50 g/g (98% of theoretical and substrate conversion 99%.     

Continuous anaerobic treatment of wastewater from a kraft pulp mill

A pilot-scale study of the thermophilic anaerobic digestion of high-strength wastewater (evaporator condensate, EC) discharged from a kraft pulp production process was performed. The system consisted of a microfiltration (MF) membrane module for oily substances removal, a stripping system using evolved gas from the digester for sulfur compounds removal, an anaerobic fixed-bed bioreactor for methane fermentation, and an ultrafiltration (UF) membrane module for retention of a high density of bacterial cells. The bioreactor had a fixed-bed with an effective volume of 5 m³ packed with pumice stone. In a continuous run with only the MF membrane module for oily substances removal, the digester efficiency declined because of methanogenic inhibition by sulfur compounds. After fitting of the stripping system which used evolved gas from the digester, the inhibitive sulfur compounds in the EC were removed more than 80%, and high-loading and high-efficiency operation could be attained. The BOD loading and BOD removal of 35.5 kg BOD/m³/d and 93%, respectively were attained. By anaerobic treatment of the evaporator condensate waste before the conventional aerobic activated sludge method, the total costs would be reduced to ¥3.31/m³ wastewater compared with ¥4.53/m³-wastewater by the aerobic activated sludge method only. The stability of digester performance against interruption by feed stoppage was also examined.     

Rapid production of Pediococcus halophilus salt-tolerant cells by a cultivation method employing gradual increases in NaCl concentration using a fermentor with a microfiltration module

A new fermentation system employing gradual increases in the NaCl concentration of the culture medium was developed for the rapid production of Pediococcus halophilus NaCl-tolerant cells. A fermentation system with cross-flow filtration using a micro-filtration module allowed the continuous removal of inhibitory metabolites and complete recycling of the cells to the fermentor. By increasing the NaCl concentrations stepwise or linearly in the feeding media, cells of 8.48 or 9.86 g-dry weight per liter were obtained. The productivities of NaCl-tolerant cells per unit time in a cultivation with a stepwise or linear increase in NaCl concentration in the feeding media were 46 or 56-fold as high, repectively, as that in conventional batch cultivation.     

Bioconversion of tea polyphenols to bioactive theabrownins by Aspergillus fumigatus

Theabrownins (TB) are water-soluble phenolic compounds associated with the various health benefits of Pu-erh tea, a post-fermented Chinese dark tea. This work reports on the production of theabrownins from infusions of sun-dried green tea leaves using a pure culture of Aspergillus fumigatus isolated from a solid-state Pu-erh tea fermentation. A theabrownins yield of 158 g kg^?1 sun-dried green tea leaves was obtained in 6 days at 45 °C in an aerobic fermentation. In a 2 l fermenter, the yield of theabrownins was 151 g kg^?1 sun-dried green tea leaves in 48 h of aerobic culture (45 °C, 1 vvm aeration rate, 250 rpm agitation speed). Extracellular polyphenol oxidase and peroxidase of A. fumigatus contributed to this bioconversion. Repeated batch fermentation process was used for producing theabrownins but was less productive than the batch process.     

Pullulan production by a non-pigmented strain of Aureobasidium pullulans using batch and fed-batch culture

The production of pigment-free pullulan by Aureobasidium pullulans in batch and fed-batch culture was investigated. Batch culture proved to be a better fermentation system for the production of pullulan than the fed-batch culture system. A maximum polysaccharide concentration (31.3 g l⁻¹), polysaccharide productivity (4.5 g l⁻¹ per day), and sugar utilization (100%) were obtained in batch culture. In fed-batch culture, feed medium composition influenced the kinetics of fermentation. For fed-batch culture, the highest values of pullulan concentration (24.5 g l⁻¹) and pullulan productivity (3.5 g l⁻¹ per day) were obtained in culture grown with feeding substrate containing 50 g l⁻¹ sucrose and all nutrients. The molecular size of pullulan showed a decline as fermentation progressed for both fermentation systems. At the end of fermentation, the polysaccharide isolated from the fed-batch culture had a slightly higher molecular weight than that of batch culture. Structural characterization of pullulan samples (methylation and enzymic hydrolysis with pullulanase) revealed the presence of mainly α-(1→4) (∼66%) and α-(1→6) (∼31%) glucosidic linkages; however, a small amount (<3%) of triply linked (1,3,4-, 1,3,6-, 1,2,4- and 1,4,6-Glc p) residues were detected. The molecular homogeneity of the alcohol-precipitated polysaccharides from the fermentation broths as well as the structural features of pullulan were confirmed by ¹³C-NMR and pullulanase treatments followed by gel filtration chromatography of the debranched digests.     

Very high density of Chinese hamster ovary cells in perfusion by alternating tangential flow or tangential flow filtration in WAVE bioreactor™—part II: Applications for antibody production and cryopreservation

A high cell density perfusion process of monoclonal antibody (MAb) producing Chinese hamster ovary (CHO) cells was developed in disposable WAVE Bioreactor? using external hollow fiber (HF) filter as cell separation device. Tangential flow filtration (TFF) and alternating tangential flow (ATF) systems were compared and process applications of high cell density perfusion were studied here: MAb production and cryopreservation. Operations by perfusion using microfiltration (MF) or ultrafiltration (UF) with ATF or TFF and by fed‐batch were compared. Cell densities higher than 10⁸ cells/mL were obtained using UF TFF or UF ATF. The cells produced comparable amounts of MAb in perfusion by ATF or TFF, MF or UF. MAbs were partially retained by the MF using ATF or TFF but more severely using TFF. Consequently, MAbs were lost when cell broth was discarded from the bioreactor in the daily bleeds. The MAb cell‐specific productivity was comparable at cell densities up to 1.3 × 10⁸ cells/mL in perfusion and was comparable or lower in fed‐batch. After 12 days, six times more MAbs were harvested using perfusion by ATF or TFF with MF or UF, compared to fed‐batch and 28× more in a 1‐month perfusion at 10⁸ cells/mL density. Pumping at a recirculation rate up to 2.75 L/min did not damage the cells with the present TFF settings with HF short circuited. Cell cryopreservation at 0.5 × 10⁸ and 10⁸ cells/mL was performed using cells from a perfusion run at 10⁸ cells/mL density. Cell resuscitation was very successful, showing that this system was a reliable process for cell bank manufacturing. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:768–777, 2013     

Integrated production of lactic acid and biomass on distillery stillage

The possibilities of parallel lactic acid and biomass production in batch and fed-batch fermentation on distillery stillage from bioethanol production were studied. The highest lactic acid yield and productivity of 92.3 % and 1.49 g L^?1 h^?1 were achieved in batch fermentation with initial sugar concentration of 55 g L^?1. A significant improvement of the process was achieved in fed-batch fermentation where the concentration of lactic acid was increased to 47.6 % and volumetric productivity for 21 % over the batch process. A high number of Lactobacillus rhamnosus ATCC 7469 viable cells of 10⁹ CFU ml^?1 was attained at the end of fed-batch fermentation. The survival of 92.9 % of L. rhamnosus cells after 3 h of incubation at pH 2.5 validated that the fermentation media remained after lactic acid removal could be used as a biomass-enriched animal feed thus making an additional value to the process.     

Co-production of biomass and metabolites by cell retention culture of <Emphasis Type="Italic">Leuconostoc citreum</Emphasis>

Cell retention culture of lactic acid bacterium Leuconostoc citreum was carried out in a fermentor equipped with an internal ceramic filtration system to co-produce biomass and metabolites. The filtration system was composed of porous ceramic filter module with pore size of 0.1 μm and total surface area of 330 cm². High cell density cultivation of L. citreum was achieved within the fermentor, while extracellular metabolites such as mannitol and d-lactic acid were produced through the filter with high productivities. In batch culture of L. citreum using a medium containing 50 g/L of glucose and 100 g/L of fructose, the maximum optical density (OD) monitored at 660 nm was 13 with 65 g/L of mannitol and 38 g/L of lactic acid. In cell retention culture of L. citreum with dilution rate of 0.07 h⁻¹, OD increased to 75, which was 6 times higher than that in batch culture. The concentrations of mannitol and lactic acid increased to 85 and 45 g/L, respectively, and were maintained throughout the cultivation to 105 h. By increasing dilution rate to 0.13 h⁻¹, the productivities of mannitol and lactic acid increased to 8.5 and 4.2 g/L/h, respectively, which were 2.7 to 3 times higher than those in batch culture, suggesting that cell retention culture using internal filtration system is highly effective for co-production of useful cell biomass and various extracellular metabolites.     

Enhancing xanthine oxidase fermentation with pH-shift strategy based on kinetic analysis by Arthrobacter M3

The effect of initial culture pH and inducer concentration on xanthine oxidase (XOD) fermentation in shake flasks was first carried out. The results showed that the optimum initial culture pH and inducer concentration were 8.6 and 3.6 g/l, respectively. Batch fermentation of XOD by Arthrobacter M3 in a 7.5-l fermentor was then tested under various pH conditions ranging from 7.6 to 8.6. Based on the analysis of the obtained kinetic parameters, a pH-shift strategy in batch fermentation was implemented to enhance the XOD fermentation. In this strategy, the initial culture pH was set at 8.6 without control and was maintained at 7.6 after the biomass reached 2.0 g/l DCW. XOD production (P) and final average yield coefficient for production on biomass (FAY_p/x) in this strategy reached 7,415.3 U/l and 1,229.7 U/g, respectively, which were significantly higher than the results from the other four protocols. In pH-shift batch fermentation, the Luedeking–Piret equation for product accumulation and the Luedeking–Piret-like equation for substrate consumption fit well with the experimental values. The correlation coefficients (R ²) of these two fitting curves were 0.977 and 0.992, respectively.     

Comparing the xylose reductase/xylitol dehydrogenase and xylose isomerase pathways in arabinose and xylose fermenting Saccharomyces cerevisiae strains

Background

Ethanolic fermentation of lignocellulosic biomass is a sustainable option for the production of bioethanol. This process would greatly benefit from recombinant Saccharomyces cerevisiae strains also able to ferment, besides the hexose sugar fraction, the pentose sugars, arabinose and xylose. Different pathways can be introduced in S. cerevisiae to provide arabinose and xylose utilisation. In this study, the bacterial arabinose isomerase pathway was combined with two different xylose utilisation pathways: the xylose reductase/xylitol dehydrogenase and xylose isomerase pathways, respectively, in genetically identical strains. The strains were compared with respect to aerobic growth in arabinose and xylose batch culture and in anaerobic batch fermentation of a mixture of glucose, arabinose and xylose.

Results

The specific aerobic arabinose growth rate was identical, 0.03 h^-1, for the xylose reductase/xylitol dehydrogenase and xylose isomerase strain. The xylose reductase/xylitol dehydrogenase strain displayed higher aerobic growth rate on xylose, 0.14 h^-1, and higher specific xylose consumption rate in anaerobic batch fermentation, 0.09 g (g cells)^-1 h^-1 than the xylose isomerase strain, which only reached 0.03 h^-1 and 0.02 g (g cells)^-1h^-1, respectively. Whereas the xylose reductase/xylitol dehydrogenase strain produced higher ethanol yield on total sugars, 0.23 g g^-1 compared with 0.18 g g^-1 for the xylose isomerase strain, the xylose isomerase strain achieved higher ethanol yield on consumed sugars, 0.41 g g^-1 compared with 0.32 g g^-1 for the xylose reductase/xylitol dehydrogenase strain. Anaerobic fermentation of a mixture of glucose, arabinose and xylose resulted in higher final ethanol concentration, 14.7 g l^-1 for the xylose reductase/xylitol dehydrogenase strain compared with 11.8 g l^-1 for the xylose isomerase strain, and in higher specific ethanol productivity, 0.024 g (g cells)^-1 h^-1 compared with 0.01 g (g cells)^-1 h^-1 for the xylose reductase/xylitol dehydrogenase strain and the xylose isomerase strain, respectively.

Conclusion

The combination of the xylose reductase/xylitol dehydrogenase pathway and the bacterial arabinose isomerase pathway resulted in both higher pentose sugar uptake and higher overall ethanol production than the combination of the xylose isomerase pathway and the bacterial arabinose isomerase pathway. Moreover, the flux through the bacterial arabinose pathway did not increase when combined with the xylose isomerase pathway. This suggests that the low activity of the bacterial arabinose pathway cannot be ascribed to arabitol formation via the xylose reductase enzyme.     

Solid carriers for a Clostridium acetobutylicum that produces acetone and butanol

Several high strength solids have been tested as carriers for acetone-butanol production by Clostridium acetobutylicum ATCC 824. In batch fermentation, coke, kaolinite and Gel White (a montmorillonite clay) appeared to have a beneficial effect on this fermentation, although the effectiveness appeared to be dependent on the medium used. One of the least expensive materials, coke, was found to be suitable for use in continuous culture. Steady state conditions could be maintained for more than 30 days with total solvent production, productivity and yield of 12 g/l, 1.12 g l⁻¹h⁻¹and 0.3 g TS/g glucose used, respectively.     

Poly(β-hydroxybutyric acid) thermoplastic production by Alcaligenes latus: Behavior of fed-batch cultures

Fed-batch culture of Alcaligenes latus, ATCC 29713, was investigated for producing the intracellular bioplastic poly(β–hydroxybutyric acid), PHB. Constant rate feeding, exponentially increasing feeding rate, and pH-stat fed batch methods were evaluated. pH-stat fed batch culture reduced or delayed accumulation of the substrate in the broth and led to significantly enhanced PHB productivity relative to the other modes of feeding. Presence of excessive substrate appeared to inhibit PHB synthesis, but not the production of cells. In fed-batch culture, the maximum specific growth rate (0.265?h^?1) greatly exceeded the value (0.075?h^?1) previously observed in batch culture of the same strain. Similarly, the maximum PHB production rate (up to 1.15?g?·?l^?1?·?h^?1) was nearly 8-fold greater than values observed in batch operations. Fed-batch operation was clearly superior to batch fermentation for producing PHB. A low growth rate was not a prerequisite for PHB accumulation, but a reduced or delayed accumulation of substrate appeared to enhance PHB accumulation. Under the best conditions, PHB constituted up to 63% of dry cell mass after 12?h of culture. The average biomass yield coefficient on sucrose was about 0.35, or a little less than in batch fermentations. The highest PHB concentrations attained were about 18?g?·?l^?1.     

Overproduction of poly(β-malic acid) (PMA) from glucose by a novel Aureobasidium sp. P6 strain isolated from mangrove system

After over 100 strains of Aureobasidium spp isolated from mangrove system were screened for their ability to produce poly(β-malic acid) (PMA), it was found that Aureobasidium sp. P6 strain among them could produce high level of Ca²⁺-PMA. Fourteen percent glucose and 6.5 % CaCO₃ in the medium were the most suitable for Ca²⁺-PMA production. Then, 100.7 g/l of Ca²⁺-PMA was produced using Aureobasidium sp. P6 strain within 168 h at flask level. During 10-l batch fermentation, when the medium contained 12.0 % glucose, 98.7 g/l of Ca²⁺-PMA in the culture and 14.7 g/l of cell dry weight were obtained within 156 h, leaving 0.34 % reducing sugar in the fermented medium. When glucose concentration in the fermentation medium was 14.0 %, 118.3 g/l of Ca²⁺-PMA in the culture and 16.4 g/l of cell dry weight were obtained within 168 h, leaving 0.4 % reducing sugar in the fermented medium. After purification of Ca²⁺-PMA from the culture and acid hydrolysis of the pure Ca²⁺-PMA, analysis of HPLC showed that Aureobasidium sp. P6 strain only produced two main components of Ca²⁺-PMA and minor amount of calcium malate and that the hydrolysate of PMA was mainly composed of calcium malate. This is the first time to report that the novel yeast strain Aureobasidium sp. P6 strain isolated from the mangrove systems can produce such high amount of Ca²⁺-PMA.     

Immobilization of Lactobacillus rhamnosus in polyvinyl alcohol/calcium alginate matrix for production of lactic acid

Immobilization of Lactobacillus rhamnosus ATCC7469 in poly(vinyl alcohol)/calcium alginate (PVA/Ca-alginate) matrix using “freezing–thawing” technique for application in lactic acid (LA) fermentation was studied in this paper. PVA/Ca-alginate beads were made from sterile and non-sterile PVA and sodium alginate solutions. According to mechanical properties, the PVA/Ca-alginate beads expressed a strong elastic character. Obtained PVA/Ca-alginate beads were further applied in batch and repeated batch LA fermentations. Regarding cell viability, L. rhamnosus cells survived well rather sharp immobilization procedure and significant cell proliferation was observed in further fermentation studies achieving high cell viability (up to 10.7 log CFU g⁻¹) in sterile beads. In batch LA fermentation, the immobilized biocatalyst was superior to free cell fermentation system (by 37.1%), while the highest LA yield and volumetric productivity of 97.6% and 0.8 g L⁻¹ h⁻¹, respectively, were attained in repeated batch fermentation. During seven consecutive batch fermentations, the biocatalyst showed high mechanical and operational stability reaching an overall productivity of 0.78 g L⁻¹ h⁻¹. This study suggested that the “freezing–thawing” technique can be successfully used for immobilization of L. rhamnosus in PVA/Ca-alginate matrix without loss of either viability or LA fermentation capability.

     

Stimulation of the rate of l-lactate fermentation using Lactococcus lactis IO-1 by periodic electrodialysis

Lactic acid fermentation in glucose medium with periodic electrodialysis by Lactococcus lactis IO-1 was examined. The fermentation time was reduced considerably, compared with the time required for ordinary built-in electrodialysis fermentation with a microfilter module (ED-MF). Fermentation with an initial glucose concentration of 80 g/l was completed within 18 h, about 50% of the time required with an ED-MF. The maximum productivity of this novel system was about two-fold that of the ordinary ED-MF system even when the lactate concentration in broth was higher than in the ED-MF. The H₂ gas produced from the ED-MF made the culture redox potential (CRP) lower than in the novel system. Online culture redox potential was monitored and higher CRP indicated a higher fermentation rate.     

Production of cyclodextrin glycosyltransferase by immobilized <Emphasis Type="Italic">Bacillus</Emphasis> sp. on chitosan matrix

The whole-cell immobilization on chitosan matrix was evaluated. Bacillus sp., as producer of CGTase, was grown in solid-state and batch cultivation using three types of starches (cassava, potato and cornstarch). Biomass growth and substrate consumption were assessed by flow cytometry and modified phenol–sulfuric acid assays, respectively. Qualitative analysis of CGTase production was determined by colorless area formation on solid culture containing phenolphthalein. Scanning electron microscopy (SEM) analysis demonstrated that bacterial cells were immobilized on chitosan matrix efficiently. Free cells reached very high numbers during batch culture while immobilized cells maintained initial inoculum concentration. The maximum enzyme activity achieved by free cells was 58.15 U ml^?1 (36 h), 47.50 U ml^?1 (36 h) and 68.36 U ml^?1 (36 h) on cassava, potato and cornstarch, respectively. CGTase activities for immobilized cells were 82.15 U ml^?1 (18 h) on cassava, 79.17 U ml^?1 (12 h) on potato and 55.37 U ml^?1 (in 6 h and max 77.75 U ml^?1 in 36 h) on cornstarch. Application of immobilization technique increased CGTase activity significantly. The immobilized cells produced CGTase with higher activity in a shorter fermentation time comparing to free cells.     

High-yield export of a native heterologous protein to the periplasm by the tat translocation pathway in Escherichia coli

Numerous high‐value recombinant proteins that are produced in bacteria are exported to the periplasm as this approach offers relatively easy downstream processing and purification. Most recombinant proteins are exported by the Sec pathway, which transports them across the plasma membrane in an unfolded state. The twin‐arginine translocation (Tat) system operates in parallel with the Sec pathway but transports substrate proteins in a folded state; it therefore has potential to export proteins that are difficult to produce using the Sec pathway. In this study, we have produced a heterologous protein (green fluorescent protein; GFP) in Escherichia coli and have used batch and fed‐batch fermentation systems to test the ability of the newly engineered Tat system to export this protein into the periplasm under industrial‐type production conditions. GFP cannot be exported by the Sec pathway in an active form. We first tested the ability of five different Tat signal peptides to export GFP, and showed that the TorA signal peptide directed most efficient export. Under batch fermentation conditions, it was found that TorA‐GFP was exported efficiently in wild type cells, but a twofold increase in periplasmic GFP was obtained when the TatABC components were co‐expressed. In both cases, periplasmic GFP peaked at about the 12 h point during fermentation but decreased thereafter, suggesting that proteolysis was occurring. Typical yields were 60 mg periplasmic GFP per liter culture. The cells over‐expressed the tat operon throughout the fermentation process and the Tat system was shown to be highly active over a 48 h induction period. Fed‐batch fermentation generated much greater yields: using glycerol feed rates of 0.4, 0.8, and 1.2 mL h^?1, the cultures reached OD₆₀₀ values of 180 and periplasmic GFP levels of 0.4, 0.85, and 1.1 g L^?1 culture, respectively. Most or all of the periplasmic GFP was shown to be active. These export values are in line with those obtained in industrial production processes using Sec‐dependent export approaches. Biotechnol. Bioeng. 2012; 109: 2533–2542. © 2012 Wiley Periodicals, Inc.