A novel feeding strategy for enhanced protein production by fed-batch fermentation in recombinant Pichia pastoris

A novel feeding strategy for enhanced protein production of hepatitis B virus surface antigen (HBsAg) in fed-batch fermentation, recombinant Pichia pastoris, has been developed. A minimal salt medium was used to grow cells in the initial batch fermentation, followed by a glycerol+salts fed-batch phase. At the end of the fed-batch phase a dry cell weight of 130 g l⁻¹ was achieved. In the absence of basal salts, the same amount of glycerol feed resulted in only 90 g l⁻¹ cell dry weight. When a limited amount of casamino acids were also included every 24 h during methanol induction, there was a two-fold increase in expression levels of HBsAg. After 192 h of induction, the expression levels of HBsAg (soluble and insoluble) reached >1 g l⁻¹ using the Mut⁻ strain. Thus, the use of basal salts in the glycerol feed, along with the addition of limited amounts of casamino acids with the methanol feed, resulted in an increased expression of total HBsAg.     

A model-based feeding strategy for fed-batch fermentation of recombinant Pichia pastoris

A two stage, exponential feeding strategy with mixed glycerol/methanol substrate was used in a fed-batch recombinant Pichia pastorisfermentation. The feeding strategy was developed using a simple model based on mass balances, Monod-type growth kinetics, and constant specific heterologous protein production rate. The model accurately predicted cell growth, and demonstrated the usefulness of a rational, model-based approach for improving the productivity of recombinant P. pastoris fermentation.     

Sorbitol as a non-repressing carbon source for fed-batch fermentation of recombinant Pichia pastoris

Glycerol/methanol and sorbitol/methanol mixed-feed fermentation strategies for the production of recombinant proteins by Pichia pastoris were compared in order to examine sorbitol's potential as a carbon source. Although P. pastoris does have a lower cell yield on sorbitol than on glycerol, the specific rate of product formation is higher (60 g protein g^–1 dry wth for sorbitol/methanol, vs 45 g protein g^–1 dry wth for glycerol/methanol), resulting in comparable final recombinant expression levels. Importantly, the presence of residual sorbitol in the growth medium appears to be less repressive to the alcohol oxidase promoter in this organism, providing a more forgiving means of operating mixed-feed fed-batch recombinant P. pastoris fermentations.     

Hypoxic fed-batch cultivation of Pichia pastoris increases specific and volumetric productivity of recombinant proteins

High cell density cultivation of Pichia pastoris has to cope with several technical limitations, most importantly the transfer of oxygen. By applying hypoxic conditions to chemostat cultivations of P. pastoris expressing an antibody Fab fragment under the GAP promoter, a 2.5-fold increase of the specific productivity q(P) at low oxygen supply was observed. At the same time the biomass decreased and ethanol was produced, indicating a shift from oxidative to oxidofermentative conditions. Based on these results we designed a feedback control for enhanced productivity in fed batch processes, where the concentration of ethanol in the culture was kept constant at approximately 1.0% (vv(-1)) by a regulated addition of feed medium. This strategy was tested successfully with three different protein producing strains, leading to a three- to sixfold increase of the q(P) and threefold reduced fed batch times. Taken together the volumetric productivity Q(P) increased 2.3-fold.     

Phytase production by fermentation of recombinant Pichia pastoris in monosodium glutamate wastewater

A novel method is proposed to produce both phytase and single-cell protein in recombinant Pichia pastoris fermentation using monosodium glutamate wastewater (MSGW) as the basal medium. Recombinant P. pastoris MR33 transformed with a phytase gene (AppA-m) from Escherichia coli was constructed and showed capability to utilize ammonium as the only nitrogen source. The fermentation medium was optimized in shake flasks by single-factor test and response surface methodology. A fed-batch system containing 30% MSGW, 50 g/l glucose, 1.58 g/l CaSO₄, 5.18 g/l MgSO₄ and 6.67 g/l KH₂PO₄ was developed in a 3.7-l bioreactor. The maximum phytase activity in the MSGW medium reached 3,380 U/ml, 84.2% of that in chemically defined medium, and the dry cell weight was 136 g/l. The single-cell protein (SCP; 46.66% dry cell weight) contains a variety of amino acids and is low in fat, which is ideal for utilization in animal feed. Thus, it is feasible to use MSGW medium for the production of enzymes that can be expressed in P. pastoris.     

Optimization of human serum albumin production in methylotrophic yeast Pichia pastoris by repeated fed-batch fermentation

An optimization method for repeated fed-batch fermentation was established with the aim of improving the recombinant human serum albumin (rHSA) production in Pichia pastoris. A simulation model for fed-batch fermentation was formulated and the optimal methanol-feeding policy calculated by dynamic programming method using five different methanol-feeding periods. The necessary state variables were collected from the calculated results and used for further optimization of repeated fed-batch fermentation. The optimal operation policy was investigated using the pre-collected state variables by estimating the overall profit per total methanol-feeding time. The calculated results indicated that the initial cell mass from the 2nd fed-batch fermentation on should be set at 35 or 40 g and methanol-feeding time at 264 h. In repeated fed-batch fermentation using the optimal operation policy, actual culture volume was in good agreement with the values simulated by model equations, but some discrepancy was observed in rHSA production. Minimum experiments were therefore carried out to re-evaluate rHSA production levels, which were then applied in re-calculations to determine the optimal operation policy. The optimal policy for repeated fed-batch fermentation established in the present study (i.e., 4-times-repeated fed-batch fermentation) achieved a 47% increase in annual rHSA production. Optimization of the culture period also brought about a 28% increase in annual rHSA production even in simple (not repeated) fed-batch fermentation.     

Production of recombinant protein in Pichia pastoris by fermentation

This protocol is applicable to recombinant protein expression by small-scale fermentation using the Pichia pastoris expression system. P. pastoris has the capacity to produce large quantities of protein with eukaryotic processing. Expression is controlled by a methanol-inducible promoter, which allows a biomass-generation phase before protein production is initiated. The target protein is secreted directly into a protein-free mineral salt medium, and is relatively easy to purify. The protocol is readily interfaced with expanded bed adsorption for immediate capture and purification of recombinant protein. The setting up of the bioreactor plus the fermentation itself takes 1 wk. Making the master and user seed lots takes approximately 2 wk for each individual clone.     

Two-stage glycerol feeding for enhancement of recombinant hG-CSF production in a fed-batch culture of Pichia pastoris

Recombinant hG-CSF was expressed in Pichia pastoris under the control of the AOX1 promoter. In this study, the glycerol feeding rate was adjusted to achieve the maximum attainable specific growth rate before induction. Using a two-stage glycerol feeding method, the specific growth rate was changed from a maximum value of 0.21 h⁻¹ (at the beginning of feeding) to 0.15 h⁻¹ prior to induction. With this approach, the final dry cell wt and rhG-CSF yield achieved was close to 120 g l⁻¹ and 320 mg l⁻¹, respectively. Our study found that the two-stage feeding method allowed the overall productivity of rhG-CSF to increase 2.9 times that of the conventional fed-batch method.     

Impact of methanol concentration on secreted protein production in oxygen-limited cultures of recombinant Pichia pastoris

The methylotrophic yeast Pichia pastoris is a powerful system for production of recombinant proteins, showing high ability to secrete properly folded proteins. A major plus is the strong AOX1 promoter highly induced by methanol. During growth on methanol, however, oxygen readily becomes limiting. In oxygen-limited cultivations of recombinant Pichia pastoris, the methanol concentration had a strong impact on the production of a single-chain antibody fragment (scFv). High methanol concentrations were required to compensate the lack of oxygen and fully induce recombinant protein production, at the same time reducing gratuitous biomass formation due to a lower biomass yield. Product concentrations of 60, 150, and 350 mg/L were obtained with methanol concentrations of 0.3, 1, and 3% (v/v). Moreover, accumulation of a putative product fragment that cannot be removed during affinity purification was prevented at high methanol concentrations. Cell vitality after 100 h was maintained above 98% and 96% of the culture with 0.3% and 3% methanol, respectively. In cultivations supplemented with oxygen, in contrast, methanol concentration between 0.3% and 3% did not influence the product yield of 300-400 mg/L. Thus, efficient recombinant protein production under oxygen-limitation seems to require high methanol concentrations, enabling product concentration as high as otherwise obtained only with expensive supply of pure oxygen.     

响应面分析优化产木聚糖酶毕赤酵母基因工程菌培养条件

研究不同碳源、氮源和无机盐对毕赤酵母AX181菌株产木聚糖酶的影响。实验表明,分别采用葡萄糖和玉米浆干粉为碳源和氮源可以明显提高木聚糖酶的产量。无机盐单因子优化实验显示添加适量的（NH4）2SO4、KH2PO4、MnSO4·H2O、FeSO4·7H2O也可以部分提高木聚糖酶产量。在此基础上利用响应面法优化毕赤酵母产木聚糖酶培养基,利用12次实验的Plackett—Burman设计实验筛选出影响产木聚糖酶的3个主要因素,即玉米浆干粉、MnSO4·H2O和FeSO4·7H20。并进一步通过最陡爬坡路径逼近最大响应区域,采用中心组合实验设计确定最佳条件。优化后的产木聚糖酶培养基组分为（g/L）：葡萄糖40．00,玉米浆干粉80．84,（NH4）2SO46．25,KH2PO41．25、MnSO4·H2O0．35,FeS04-7H2O1．31。培养基优化后,实际产酶2883．86u／mL,是优化前YPD培养基产酶的2．51倍。     

Response surface optimization of fermentation conditions for xylanase production by recombinant Pichia pastoris

研究不同碳源、氮源和无机盐对毕赤酵母AX181菌株产木聚糖酶的影响.实验表明,分别采用葡萄糖和玉米浆干粉为碳源和氮源可以明显提高木聚糖酶的产量.无机盐单因子优化实验显示添加适量的(NH4)2SO4、KH2 PO4、MnSO4·H2O、FeSO4·7H2O也可以部分提高木聚糖酶产量.在此基础上利用响应面法优化毕赤酵母产木聚糖酶培养基,利用12次实验的Plackett - Burman设计实验筛选出影响产木聚糖酶的3个主要因素,即玉米浆干粉、MrSO4 ·H2O和FeSO4·7H2O.并进一步通过最陡爬坡路径逼近最大响应区域,采用中心组合实验设计确定最佳条件.优化后的产木聚糖酶培养基组分为(g/L):葡萄糖40.00,玉米浆干粉80.84,(NH4)2SO4 6.25,KH2PO4 1.25、MnSO4·H2O 0.35,FeSO4 ·7H2O 1.31.培养基优化后,实际产酶2 883.86 U/mL,是优化前YPD培养基产酶的2.51倍.     

Enhancing the production of Fc fusion protein in fed-batch fermentation of Pichia pastoris by design of experiments

This study focuses on the feasibility of producing a therapeutic Fc fusion protein in Pichia pastoris (P. pastoris) and presents an optimization design of experiment (DOE) strategy in a well-defined experimental space. The parameters examined in this study include pH, temperature, salt supplementation, and batch glycerol concentration. The effects of these process conditions were captured by statistical analysis focusing on growth rate and titer responses. Batch medium and fermentation conditions were also investigated prior to the DOE study in order to provide a favorable condition to enable the production of this Fc fusion protein. The results showed that approximately 373 mg/L of the Fc fusion protein could be produced. The pH was found to be particularly critical for the production of this Fc fusion protein. It was significantly higher than the conventional, recommended pH for P. pastoris fermentation. The development of this process shows that protein production in P. pastoris is protein specific, and there is not a set of pre-defined conditions that can work well for all types of proteins. Thorough process development would need to be performed for every type of protein in order for large-scale production in P. pastoris to be feasible.     

Cell cycle model for recombinant Pichia pastoris during glycerol fed-batch cultivation

A cell cycle model is proposed for methylotrophic yeast Pichia pastoris grown on glycerol during fed-batch cultivation. Morphological differentiation of cells, such as unbudded daughter cell, unbudded parent cell and budding cell, is depicted by the model. During the cyclic growth, cells in different cycling period are assumed to undergo sequential shifting dominantly. The input of the cell cycle model is the specific growth rate, which is calculated from the macrokinetic model proposed previously. The cell cycle related variables, such as the fraction of budding cells and the cell density are then simulated. Model validation is carried out with the experimental data of off-line assays.     

Control of recombinant human endostatin production in fed-batch cultures of Pichia pastoris using the methanol feeding rate

Endostatin is a 20 kDa carboxyl-terminal fragment of collagen XVIII that strongly inhibits angiogenesis and tumor growth. The methylotrophic yeast, Pichia pastoris, is a robust expression system that can be used to study methods to improve the yields of rhEndostatin. We expressed rhEndostatin in P. pastoris under the control of the alcohol oxidase 1 (aox 1) promoter (Mut⁺ phenotype) as a model, and used a cell biomass of about 50 g l^–1 dry cell wt as a starting point for the induction phase and varied the methanol feed rate at 8 ml l^–1 h^–1, 11 ml l^–1 h^–1 and 15 ml l^–1 h^–1. While the cell growth rate was proportional to the rate of methanol delivery, protein production rate was not. These findings could be used to guide parameters for large-scale production of recombinant proteins in the P. pastoris system.     

Production of salmosin, a snake venom-derived disintegrin, in recombinant Pichia pastoris using high cell density fed-batch fermentation

Salmosin, a snake venom-derived disintegrin, was successfully expressed in the methylotrophic yeast Pichia pastoris and secreted into the culture supernatant, as a 6 kDa protein. High-cell density fermentation of recombinant P. pastoris was optimized for the mass production of salmosin. In a 5 L jar fermentor, recombinant P. pastoris was fermented in growth medium containing 5% (w/v) glycerol at the controlled pH of 5.0. After culturing for 21 h, glycerol feeding medium was fed at one time into the culture broth. After 7 h (a total of 28 h), induction medium that contained methanol was increasingly added until the culture time totaled 75 h. Finally, these optimized culture conditions produced a high cell density of recombinant P. pastoris (dry cell weight of 113.38 g/L) and led to the mass production of salmosin (a total protein concentration of 369.2 mg/L). The culture supernatant containing salmosin inhibited platelet aggregation, resulting in a platelet aggregation of 9% compared to that of 94% in the control experiment, without culture supernatant. These results demonstrate that recombinant salmosin in culture supernatant from high cell density fed-batch fermentation can serve as a platelet aggregation inhibitor.     

Improvement of recombinant hirudin production by controlling NH4 + concentration in Pichia pastoris fermentation

In recombinant Pichia pastoris fermentation for hirudin production in a 5 l fermenter, a new strategy was explored to match the short fermentation time at low NH4+ concentration with decreased hirudin degradation at high NH4+ concentration. A combination of a defined medium containing initial 0.025 m NH4+ with NH4+ addition up to 0.6 m in the growth phase was achieved in both the improvement of hirudin production and the repression of hirudin degradation. Intact and total hirudin reached 2.63 g l(-1) and 4.25 g l(-1), respectively.     

重组毕赤酵母产植酸酶发酵条件的优化

为研究优化毕赤酵母工程菌H311产植酸酶的发酵条件,采用单因素试验和L18(37)正交试验考察不同工艺条件对产酶活性的影响。结果表明:影响重组毕赤酵母产植酸酶的因素重要性从大到小依次为诱导时间、甲醇添加量、装液量、初始诱导p H、生长时间、接种量和初始生长p H,产酶最佳条件为接种量3%(体积分数)、装液量20 m L(250 m L摇瓶)、生长时间20 h,诱导时间120 h、甲醇添加量1.5%(体积分数)、生长p H 6.0、诱导p H 5.0,在此条件下进行诱导表达,植酸酶的比酶活可达334 U/m L。     

发酵重组Pichia pastoris生产腺苷甲硫氨酸的研究

在5L发酵罐中对高产S腺苷甲硫氨酸的重组Pichia pastoris发酵进行了研究。重组菌在pH5．0生长,然后调为pH6．0积累腺苷甲硫氨酸,在30℃、溶氧5％及流加甲硫氨酸和尿素的条件下培养82h后,产量达4．3g／L。     

Cyclic fed-batch culture for production of human serum albumin in Pichia pastoris

Simple cyclic fed-batch culture (cfbc), consisting of a constant medium feed with periodic withdrawals of culture, resulted in a product yield (13.4 mg protein per gram biomass) similar to that obtained using the complex multiphase industrial production strategy (13.7 mg protein per gram biomass). In cfbc, productivity was ultimately limited by the rate at which the cells could assimilate methanol. Glycerol was inhibitory to growth at high concentrations. However, product yield continued to increase as the glycerol concentration was increased. In chemostat culture, dissolved oxygen concentration influenced product yield independently of any detectable influence on cell growth.     

O-glycosylation of a recombinant carbohydrate-binding module mutant secreted by Pichia pastoris

Carbohydrate-binding modules (CBMs; previously called cellulose-binding domains) make excellent fusion partners for the immobilization or purification of polypeptides. However, their use in eukaryotic hosts has been limited by glycosylation, which interferes with the ability of the CBM to bind to cellulose. We have engineered the C-terminal carbohydrate-binding module from Cellulomonas fimi xylanase 10A such that it lacks N-glycosylation sites. This variant, called CBM2aNgly-, was produced and secreted by the methylotrophic yeast Pichia pastoris and found to be O-glycosylated. The O-linked glycans were composed entirely of mannose in a ratio of 1 mol of mannose to 4 mol of protein. The overall distribution of mannose on the O-glycosylated CBM mutant ranged from 1 to 9 mannose residues with the oligosaccharide sizes ranging from Man(1) to Man(4). MALDI-TOF (all matrix-assisted-laser-desorption time of flight) mass spectrometry (MS) was used to map the O-glycosylation to three regions of the polypeptide, each region having a maximum of 4 mannose residues attached to each. Glycans chemically released from CBM2aNgly- and analyzed by fluorophore-assisted carbohydrate electrophoresis were found to contain alpha-1,2-, alpha-1,3-, and alpha-1,6-linkages. Significantly, the O-glycosylation did not influence binding, making CBM2aNgly- a suitable fusion partner for polypeptides produced in P. pastoris and other eukaryotic hosts.