Enhancement of alkaline polygalacturonate lyase production in recombinant Pichia pastoris according to the ratio of methanol to cell concentration

Polygalacturonate lyase (PGL) production by Pichia pastoris GS115 was used as a model to study the mechanism and strategy for enhancing heterologous protein production. It was found that the ratio of methanol to cell concentration had a significant influence on PGL production. In this study, an advanced glycerol exponential feeding strategy was developed for biomass accumulation in cell growth phase, by which cell concentration reached 140 g L(-1) after 19 h glycerol feeding. In subsequent production phase, a methanol feeding profile was proposed according to the optimal ratio of methanol to cell concentration at a range of 0.163-0.171 g g(-1), and PGL activity and productivity reached 430 U mL(-1) and 4.34 U mL(-1)h(-1), respectively. The strategy for enhancing PGL production by controlling the optimal ratio may provide an alternative approach to enhance heterologous protein production with P. pastoris.     

Effect of methanol feeding strategies on production and yield of recombinant mouse endostatin from Pichia pastoris

Pichia pastoris, a methylotrophic yeast, is an efficient producer of recombinant proteins in which the heterologous gene is under the control of the methanol-induced AOX1 promoter. Hence, the accepted production procedure has two phases: In the first phase, the yeast utilizes glycerol and biomass is accumulated; in the second phase, the yeast utilizes methanol which is used both as an inducer for the expression of the recombinant protein and as a carbon source. Since the yeast is sensitive to methanol concentration, the methanol is supplied gradually to the growing culture. Three methanol addition strategies were evaluated for the purpose of optimizing recombinant endostatin production. Two strategies were based on the yeast metabolism; one responding to the methanol consumption using a methanol sensor, and the other responding to the oxygen consumption. In these two strategies, the methanol supply is unlimited. The third strategy was based on a predetermined exponential feeding rate, controling the growth rate at 0.02 h(-1), in this strategy the methanol supply is limited. Throughout the induction phase glycerol, in addition to methanol, was continuously added at a rate of 1 g L h(-1). Total endostatin production was similar in all three strategies, (400 mg was obtained from 3 L initial volume), but the amount of methanol added and the biomass produced were lower in the predetermined rate method. This caused the specific production of endostatin per biomass and per methanol to be 2 times higher in the predetermined rate than in the other two methods, making the growth control strategy not only more efficient but also more convenient for downstream processing.     

Continuous culture of Candida boidinii variant 60 growing on methanol

Summary A new variant, Candida boidinii variant 60, which is less sensitive to methanol and formaldehyde shocks was grown in continuous cultures with methanol as sole carbon source. The substrate concentration in the feeding medium was either 1% methanol or 3% methanol. Biomass production, methanol consumption, the formation of formaldehyde and gas exchange were measured at different dilution rates. With low methanol feeding (10 g/l) maximal productivity of 0.44 g biomass/l·h is obtained at a dilution rate of 0.14 h^–1. Maximal specific growth rate is 0.18 h^–1. A yield of 0.32 g biomass/g methanol was obtained and the respiration quotient was determined as 0.55. Independently of initial substrate concentration, biomass decreases if methanol and formaldehyde are accumulating in the culture broth.In the culture with high methanol feeding (30 g/l) cell concentratioon increases up to 9 g/l at D=0.04 h^–1. At higher dilution rates methanol and form-aldehyde appear in the medium. Formaldehyde is then preferably oxidized without energy advantages for the cells. It seems that this enables the cells to overcome toxic effects caused by methanol and formaldehyde.     

Oxygen uptake and citric acid production by Candida lipolytica Y 1095

The rates of oxygen uptake and oxygen transfer during cell growth and citric acid production by Candida lipolytica Y 1095 were determined. The maximum cell growth rate, 1.43 g cell/L . h, and volumetric oxygen uptake rate, 343 mg O(2)/L . h, occurred approximately 21 to 22 h after inoculation. At the time of maximum oxygen uptake, the biomass concentration was 1.3% w/v and the specific oxygen uptake rate was slightly greater than 26 mg O(2)/g cell . h. The specific oxygen uptake rate decreased to approximately 3 mg O(2)/g cell . h by the end of the growth phase.During citric acid production, as the concentration of dissolved oxygen was increased from 20% to 80% saturation, the specific oxygen uptake and specific citric acid productivity (mg citric acid/g cell . h) increased by 160% and 71%, respectively, at a biomass concentration of 3% w/v. At a biomass concentration of 5% w/v, the specific oxygen uptake and specific citric acid productivity increased by 230% and 82%, respectively, over the same range of dissolved oxygen concentrations.The effect of dissolved oxygen on citric acid yields and productivities was also determined. Citric acid yields appeared to be independent of dissolved oxygen concentration during the initial production phase; however, volumetric productivity (g citric acid/L . h) increased sharply with an increase in dissolved oxygen. During the second or subsequent production phase, citric acid yields increased by approximately 50%, but productivities decreased by roughly the same percentage due to a loss of cell viability under prolonged nitrogen-deficient conditions. (c) 1994 John Wiley & Sons, Inc.     

Sorbitol co-feeding reduces metabolic burden caused by the overexpression of a Rhizopus oryzae lipase in Pichia pastoris

To improve the specific production rate of Rhizopus oryzae lipase (ROL) in Pichia pastoris, a protein that triggers the unfolded protein response in P. pastoris, the effect of sorbitol/methanol mixed substrates was tested in batch and fed-batch cultures. Remarkably, a different substrate consumption behaviour was observed depending on the host's phenotype (Mut(+) or Mut(s)) in batch cultures: when the methanol assimilation capacity is genetically reduced (Mut(s) phenotype), both substrates were consumed simultaneously, allowing not only a higher specific growth rate but also higher lipase levels (8.7-fold) compared to those obtained by cells growing on methanol as a sole carbon source in batch culture. This effect was not observed in Mut(+) phenotype, where the two substrates were consumed sequentially and the levels of heterologous product were only slightly higher (1.7-fold). A mixed substrate strategy was also applied to a Mut(s) fed-batch culture at a low methanol concentration set-point (0.5 gl(-1)). This resulted in a 2.2-fold increase in the heterologous protein level achieved, compared with the methanol-only feeding strategy. In addition, sorbitol co-feeding permitted the achievement of higher specific growth rates, and avoided the drastic decrease of the specific production rate observed after the start of the induction phase when methanol was used as sole carbon source This resulted in a significant increase in the overall bioprocess volumetric productivity (2.2-fold) and specific productivity (1.7-fold). Moreover, whereas increased ROL gene dosage in Mut(s) strains have been previously reported to be deleterious for P. pastoris cells growing on methanol, sorbitol co-feeding allowed for sustained cell growth and lipase production.     

A rational approach to improving productivity in recombinant Pichia pastoris fermentation

A Mut(S) Pichia pastoris strain that had been genetically modified to produce and secrete sea raven antifreeze protein was used as a model system to demonstrate the implementation of a rational, model-based approach to improve process productivity. A set of glycerol/methanol mixed-feed continuous stirred-tank reactor (CSTR) experiments was performed at the 5-L scale to characterize the relationship between the specific growth rate and the cell yield on methanol, the specific methanol consumption rate, the specific recombinant protein formation rate, and the productivity based on secreted protein levels. The range of dilution rates studied was 0. 01 to 0.10 h(-1), and the residual methanol concentration was kept constant at approximately 2 g/L (below the inhibitory level). With the assumption that the cell yield on glycerol was constant, the cell yield on methanol increased from approximately 0.5 to 1.5 over the range studied. A maximum specific methanol consumption rate of 20 mg/g. h was achieved at a dilution rate of 0.06 h(-1). The specific product formation rate and the volumetric productivity based on product continued to increase over the range of dilution rates studied, and the maximum values were 0.06 mg/g. h and 1.7 mg/L. h, respectively. Therefore, no evidence of repression by glycerol was observed over this range, and operating at the highest dilution rate studied maximized productivity. Fed-batch mass balance equations, based on Monod-type kinetics and parameters derived from data collected during the CSTR work, were then used to predict cell growth and recombinant protein production and to develop an exponential feeding strategy using two carbon sources. Two exponential fed-batch fermentations were conducted according to the predicted feeding strategy at specific growth rates of 0.03 h(-1) and 0.07 h(-1) to verify the accuracy of the model. Cell growth was accurately predicted in both fed-batch runs; however, the model underestimated recombinant product concentration. The overall volumetric productivity of both runs was approximately 2.2 mg/L. h, representing a tenfold increase in the productivity compared with a heuristic feeding strategy.     

Ethanol production from concentrated whey permeate using a fed-batch culture ofKluyveromyces fragilis

Summary Fed-batch fermentation of non-supplemented concentrated whey permeate resulted in high ethanol productivity for feeds of lactose for which batch fermentation had a poor performance. At an initial lactose concentration of 100 g/L and a constant lactose feeding rate of 18 g/h we have obtained: ethanol concentration 64 g/L, ethanol productivity 3.3 g/Lh, lactose consumption 100%, ethanol yield 0.47 g/g, and biomass yield 0.058 g/g.Nomenclature St total lactose fed per medium volume in the bioreactor, g/L - Si initial lactose concentration, g/L - F lactpse feeding rate, g/h - P final ethanol concentration, g/L - Y_p/s ethanol yield, g ethanol/g lactose - Y_x/s biomass yield, g biomass/g lactose - X_S lactose consumption, % - Qp overall ethanol volumetric productivity, g/Lh - m maximum specific growth rate, h - qsm maximum specific lactose consumption rate, g/gh - qpm maximum specific ethanol production rate, g/gh     

表达血管生长抑制素的重组毕赤酵母在诱导阶段混合碳源的流加

为进行高密度发酵并实现外源基因的高表达,在表型为Mut^S的重组毕赤酵母（Pichia pastoris）表达人血管生长抑制素的诱导阶段,采用了甘油甲醇混合补料的培养方式。以溶氧水平作为甘油代谢指针来控制甘油限制性流加既可维持一定菌体生长,又不会发生发酵液中残余甘油及有害代谢产物（乙醇）阻遏蛋白表达。当表达阶段的菌体平均比生长速率控制于0.012h^-1,菌体浓度达150 g/L,血管生长抑制素浓度最高达到108 mg/L,血管生长抑制素的平均比生产速率为0.02 mg/(g·h),菌体关于甘油的表观得率为0.69 g/g,菌体关于甲醇的表观得率为0.93g/g,较没有采用甘油限制性流加时都有所提高。     

Continuous ethanol production from Jerusalem artichoke tubers. I. Use of free cells of Kluyveromyces marxianus

The Continuous fermentation of Jerusalem artichoke juice to ethanol by free cells of Kluyveromyces marxianus UCD (FST) 55-82 has been studied in a continuous-stirred-tank bioreactor at 35 degrees C and pH 4.6. A maximum yield of 90% of the theoretical was obtained at a dilution rate of 0.05 h(-1). About 95% of the sugars were utilized at dilution rates lower than 0.15 h(-1). Volumetric ethanol productivity and volumetric biomass productivity reached maximum values of 7 g ETOH/L/h and 0.6 g dry wt/L/h, respectively, at a dilution rate of 0.2 h(-1). The maintenance energy coefficient for K. marxianus culture was found to be 0.46 g sugar/g biomass/h/ Oscillatory behavior was following a change in dilution rate from a previous steady state and from batch to continuous culture. Values of specific ethanol production rate and specific sugar uptake were found to increase almost linearly with the increase of the dilution rate. The maximum specific ethanol production rate and maximum specific sugar uptake rate were found to be 2.6 g ethanol/g/ cell/h and 7.9 sugars/g cell/h, respectively. Washout occurred at a dilution rate of 0.41 h(-1).     

Production of ethanol by Clostridium thermosaccharolyticum: I. Effect of cell recycle and environmental parameters

The direct microbial conversion (DMC) process for the production of ethanol from lignocellulosic biomass is limited by low volumetric ethanol production rates due to the low cell densities of Clostridium thermosaccharolyticum which is a key organism for ethanol production in this process. Hence, this study focuses on the use of a continuous- culture cell recycle system to improve the volumetric ethanol productivity and yield of the fermentation of xylose by C. thermosaccharolyticum. Early experiments with the continuous-culture cell recycle system showed a two-fold improvement in volumetric ethanol productivity. However, the ethanol yield at the higher dilution rates suffered because of the large amount of lactate produced. The manipulation of two environmental parameters-iron concentration in the nutrient medium and the N(2) purge rate of the fermentor headspace-allowed a dramatic reduction in the lactate production and a simultaneous improvement in the ethanol titer and yield. Under the improved conditions of increased iron concentration (12.5 mg/L FeSO(4) . 7H(2)O) and decreased N(2) purge rate (0.1 L/min), a continuous culture of C. thermosaccharolyticum operating at a dilution rate of 0.24 h(-1) and 50% cell recycle produced 8.6 g/L ethanol and less than 1 g/L each of acetate and lactate. The volumetric ethanol productivity was 2.2 g/L/h, which is 8 times larger than obtained for a continuous culture operated with no cell recycle and the same specific growth rate.     

甲醇抑制时重组毕赤酵母发酵的特性研究

本文对毕赤酵母进行了恒化培养研究。以甲醇为唯一碳源时,在稀释率较低时(D<0.048 h^-1),连续培养系统操作很稳定。但在稀释率高时(D>0.048h^-1),连续培养系统的定态点不止一个,实验不能维持,故采用比生长速率恒定的分批流加培养进行研究。结果表明,毕赤酵母的生长符合Andrew普遍化底物抑制模型。综合考虑水蛭素的生成、底物的消耗,在生产中维持甲醇浓度为限制性浓度(0.5 g/L),且维持比生长速率为0.02 h^-1时,水蛭素Hir65的比生成速率达到最大值0.2 mg/(g·h)且甲醇的比消耗速率为0.04 g/(g·h)。     

Purified crude glycerol by acid treatment allows to improve lipid productivity by Yarrowia lipolytica SKY7

In this study, crude glycerol with high potassium concentration was purified using acid treatment and used as carbon source for lipid production using Yarrowia lipolytica SKY7. The crude glycerol was purified using phosphoric acid (pH 2) followed by centrifugation. When purified glycerol was used as carbon source for fermentation, higher biomass productivity (0.54 g/L/h) and lipid productivity (0.2 g/L/h) was observed at 96 h compared to crude glycerol. Results indicated that 6.32 g/L potassium in crude glycerol medium was inhibitory for cell growth and lipid production by Y. lipolytica. Yield coefficients, productivities and specific growth rates were calculated for each glycerol medium. The process performance with purified glycerol medium was comparable to that of pure glycerol medium. A higher lipid yield was obtained in purified glycerol medium (0.21 g/g glycerol) than crude glycerol medium (0.124 g/g glycerol). During purification of crude glycerol, KH₂PO₄ was also produced as by-product. This study provides a way for valorization of crude glycerol with high potassium concentration for microbial lipid production.     

Analysis of single-chain antibody production in Pichia pastoris using on-line methanol control in fed-batch and mixed-feed fermentations.

In the last few years the Pichia pastoris expression system has been gaining more and more interest for the expression of recombinant proteins. Many groups have employed fermentation technology in their investigations because the system is fairly easy to scale up and suitable for the production in the milligram to gram range. A large number of heterologous proteins from different sources has been expressed, but the fermentation process technology has been investigated to a lesser extent. A large number of fermentations are carried out in standard bioreactors that may be insufficiently equipped to meet the demands of high-cell-density fermentations of methylotrophic yeasts. In particular, the lack of on-line methanol analysis leads to fermentation protocols that may impair the optimal expression of the desired products. We have used a commercially available methanol sensor to investigate in detail the effects of supplementary glycerol feeding while maintaining a constant methanol concentration during the induction of a Mut(+) strain of Pichia pastoris. Specific glycerol feed rates in the range of 38-4.2 mg. g(-1). h(-1) (mg glycerol per gram fresh weight per hour) were investigated. Expression of the recombinant scFv antibody fragment was only observed at specific feed rates below 6 mg. g(-1). h(-1). At low specific feed rates, growth was even lower than with methanol as the sole carbon source and the harvest expression level of the scFv was only half of that found in the control fermentation. These results show that glycerol inhibits expression driven by the AOX1 promoter even at extremely limited availability and demonstrate the benefits of on-line methanol control in Pichia fermentation research.     

Citric acid production by Candida lipolytica Y 1095 in cell recycle and fed-batch fermentors

The effect of dissolved oxygen on citric acid production and oxygen uptake by Candida lipolytica Y 1095 was evaluated in cell recycle and fed-batch fermentation systems. The maximum observed volumetric productivity, which occurred at a dilution rate of 0.06 h(-1), a dissolved oxygen concentration of 80%, and a biomass concentration of 5% w/v, in the cell recycle system, was 1.32 g citric acid/L . h. At these same conditions, the citric acid yield was 0.65 g/g and the specific citric acid productivity was 24.9 mg citric acid/g cell . h. In the cell recycle system, citric acid yields ranged from 0.45 to 0.72 g/g. Both the volumetric and specific citric acid productivities were dependent on the dilution rate and the concentration of dissolved oxygen in the fermentor. Similar productivities (1.29 g citric acid/L . h) were obtained in the fed-batch system operated at a cycle time of 36 h, a dissolved oxygen concentration of 80%, and 60 g total biomass. Citric acid yields in the fed-batch fermentor were consistently lower than those obtained in the cell recycle system and ranged from 0.40 to 0.59 g/g. Although citric acid yields in the fed-batch fermentor were lower than those obtained in the cell recycle system, higher citric:isocitric acid ratios were obtained in the fed-batch fermentor. As in the cell recycle system, both the volumetric and specific citric acid productivities in the fed-batch fermentor were dependent on the cycle time and dissolved oxygen concentration. (c) 1995 John Wiley & Sons, Inc.     

Establishment of cultivating strategy for highly aggregated mycelia of Morchella esculenta in a stirred-tank bioreactor

Mycelia of Morchella esculenta were found to aggregate rapidly in a submerged culture, which caused the decrease in dispersed mycelia and the problem of diffusion limitation. The effect of different agitation schemes on the growth of mycelia was investigated in a stirred-tank bioreactor. At the constant speed of 100 or 300?rpm, rapid aggregation caused the biomass concentration to drop to zero in 30?h, which was even worse than achieved under static culture. Intermittent agitation maintained a higher mycelium fragment concentration for 48?h and enhanced the biomass concentration to 4.73?g/L at 120?h. The operation with a polytron connection disrupted effectively mycelium aggregation, thus increasing the specific growth rate, biomass concentration and maximum productivity to 0.0613 1/h, 7.73?g/L and 0.0878?g/L?h at 88?h, respectively. Moreover, logistic equations and genetic algorithm (GA) were used for the simulation of biomass growth and estimation of all kinetic coefficients. The operating strategy developed in this study could be used for the production of highly aggregated mycelia, which could also achieve a high cell-density culture in a stirred tank reactor.     

Modeling Pichia pastoris growth on methanol and optimizing the production of a recombinant protein, the heavy-chain fragment C of botulinum neurotoxin, serotype A

An unstructured growth model for the recombinant methylotrophic yeast P. pastoris Mut(+) expressing the heavy-chain fragment C of botulinum neurotoxin serotype A [BoNT/A(H(c))], was successfully established in quasi-steady state fed-batch fermentations with varying cell densities. The model describes the relationships between specific growth rate and methanol concentration, and the relationships between specific methanol and ammonium consumption rates and specific growth rate under methanol-limited growth conditions. The maximum specific growth rate (mu) determined from the model was 0.08 h(-1) at a methanol concentration of 3.65 g/L, while the actual maximum mu was 0.0709 h(-1). The maximum specific methanol consumption rate was 0.0682 g/g WCW/h. From the model, growth can be defined as either methanol-limited or methanol-inhibited and is delineated at a methanol concentration of 3.65 g/L. Under inhibited conditions, the observed biomass yield (Y(X/MeOH)) was lower and the maintenance coefficient (m(MeOH)) was higher than compared to limited methanol conditions. The Y(X/MeOH) decreased and m(MeOH) increased with increasing methanol concentration under methanol-inhibited conditions. BoNT/A(H(c)) content in cells (alpha) under inhibited growth was lower than that under limited growth, and decreased with increasing methanol concentration. A maximum alpha of 1.72 mg/g WCW was achieved at a mu of 0.0267 h(-1) and induction time of 12 h.     

Direct and efficient ethanol production from high-yielding rice using a Saccharomyces cerevisiae strain that express amylases

Efficient ethanol producing yeast Saccharomyces cerevisiae cannot produce ethanol from raw starch directly. Thus the conventional ethanol production required expensive and complex process. In this study, we developed a direct and efficient ethanol production process from high-yielding rice harvested in Japan by using amylase expressing yeast without any pretreatment or addition of enzymes or nutrients. Ethanol productivity from high-yielding brown rice (1.1g/L/h) was about 5-fold higher than that obtained from purified raw corn starch (0.2g/L/h) when nutrients were added. Using an inoculum volume equivalent to 10% of the fermentation volume without any nutrient supplementation resulted in ethanol productivity and yield reaching 1.2g/L/h and 101%, respectively, in a 24-h period. High-yielding rice was demonstrated to be a suitable feedstock for bioethanol production. In addition, our polyploid amylase-expressing yeast was sufficiently robust to produce ethanol efficiently from real biomass. This is first report of direct ethanol production on real biomass using an amylase-expressing yeast strain without any pretreatment or commercial enzyme addition.     

产HSA—CP融合蛋白毕赤酵母的发酵条件优化

为提高重组毕赤酵母生产人血清白蛋白-C肽融合蛋白（HSA—CP）的产量和生产强度,在摇瓶条件下考察了甲醇诱导时间和浓度对目的蛋白产量的影响。结果表明,质量浓度10g/L的甲醇诱导72h最适于产物表达。通过对7L发酵罐中各因素的优化,得到最佳条件为：初始甘油质量浓度10g/L,30℃培养,菌体生长期和诱导期的pH及溶氧分别控制在pH5．0、30％溶解O2或pH6．0、15％的溶解O2。10g/L的甲醇诱导72h,最终使干细胞质量浓度达到56．43g/L,目的蛋白产量达368．45mg／L。生产强度为3．920mg/（L·h）,目标蛋白的比生产速率为5．12mg/（L·h）。     

Butanediol production by Aerobacter aerogenes NRRL B199: effects of initial substrate concentration and aeration agitation

Butanediol production by Aerobacter aerogenes NRRL B199 grown on glucose requires an optimal rate of aeration for the obtention of butanediol 2, 3. In the absence of air, Aerobacter aerogenes NRRL B199 growth and production are weak. Agitation-aeration is necessary for producing the biomass, but an excess of oxygen proves to be toxic with regard to metabolite production. Oxygen is a limiting substrate with regard to growth and an inhibitor with regard to the specific metabolite productivity. This observation is discussed from a kinetic stand point and in relation to the search for the optimum oxygen transfer coefficient (K(L)a), which is found to be in the range of 50-100h(-1). It has also been observed that K(L)a increases during the fermentation cycle. The initial substrate concentration effects the yield production of biomass and butanediol production. Low yields of butanediol are obtained at low initial sugar concentrations, but good yields of butanediol are obtained (0.45 g/g) at high concentrations of glucose (195 g/L). Carbon substrates and butanediol are inhibitors of cell growth while butanediol is not quite an inhibitor of the specific rate of butanediol production for the range of butanediol of 0-100 g/L.     

双碳源流加对重组毕赤酵母高效表达葡萄糖氧化酶的影响

葡萄糖氧化酶(GOD)是一种具有广泛应用前景的工业酶.为了实现葡萄糖氧化酶的高效生产,提高重组毕赤酵母生产GOD的产量和增强生产强度,对重组毕赤酵母诱导阶段的初始菌体浓度和甲醇浓度进行了优化.在此基础上,诱导期采用了双碳源(甘油、山梨醇和甘露醇)与甲醇混合流加的模式.研究发现,最佳诱导前初始菌体浓度和甲醇浓度分别为100 g/L和18 g/L,此时GOD产量为427.6 U/mL.在诱导阶段采用甘油、山梨醇和甘露醇与甲醇的混合添加均可以提高GOD产量,其中甘露醇与甲醇的混合流加效果最为显著.当甲醇与甘露醇混合流加的比例为20∶1(W/W)时,诱导156h GOD产量和生产强度分别可达711.3 U/mL和4.60 U/(mL·h),比甲醇单一流加策略结果分别提高了66.3％和67.9％.此外采用合适的甘露醇混合流加策略不但不会抑制AOX1启动子的表达,甚至有一定促进作用,AOX酶活性为8.8 U/g(对照为5.2 U/g).双碳源流加方式还能推广到毕赤酵母其他表型中,为该系统高效表达外源蛋白提供一种新策略.