Influence of specific growth rate on specific productivity and glycosylation of a recombinant avidin produced by aPichia pastoris Mut+ strain

Metabolic heat based specific growth rate estimators: Does the choice of estimation model influence the state of bioprocesses?

Accurate and reliable estimation of specific growth rate (μ) in real-time is pivotal for reliable process monitoring of a bioprocess and subsequent implementation of advanced control strategies. Gibbs free energy dissipation is imminent for any biological system, and the metabolic heat flow measurements (calorimetry) formed the basis for estimating μ. However, the rationale behind selecting a suitable μ estimator model based on calorimetric perspective remains unexplored. The present investigation addresses the notion behind the selection of an appropriate estimator for μ and the assessment of the estimator models was illustrated using different types of energy metabolism, namely, high exothermic and low exothermic processes. The results indicated that the μ values from the instantaneous heat flow estimator significantly deviated (10-fold higher) from the offline values for highly exothermic process. Notably, the cumulative heat-based estimator accurately estimated μ values on both types of energy metabolism with performance metrics <0.005 h-1.

Optimization of dilution rate and mixed carbon feed for continuous production of recombinant plant sucrose:sucrose 1-fructosyltransferase in Komagataella phaffii

The trisaccharide 1-kestose, a major constituent of commercial fructooligosaccharide (FOS) formulations, shows a superior prebiotic effect compared to higher-chain FOS. The plant sucrose:sucrose 1-fructosyltransferases (1-SST) are extensively used for selective synthesis of lower chain FOS. In this study, enhanced recombinant (r) 1-SST production was achieved in Komagataella phaffii (formerly Pichia pastoris) containing three copies of a codon-optimized Festuca arundinacea 1-SST gene. R1-SST production reached 47 U/mL at the shake-flask level after a 96-h methanol induction phase. A chemostat-based strain characterization methodology was adopted to assess the influence of specific growth rate (µ) on cell-specific r1-SST productivity (Qp) and cell-specific oxygen uptake rate (Qo) under two different feeding strategies across dilution rates from 0.02 to 0.05 h-1. The methanol-sorbitol co-feeding strategy significantly reduced Qo by 46 ± 2.4% compared to methanol-only feeding without compromising r1-SST productivity. Based on the data, a dilution rate of 0.025 h-1 was applied for continuous cultivation of recombinant cells to achieve a sustained r1-SST productivity of 5000 ± 64.4 U/L/h for 15 days.

Production, purification, and characterization of recombinant rabies virus glycoprotein expressed in PichiaPink™ yeast

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The rabies virus glycoprotein was produced in the Pichia pastoris production strains PichiaPink™ .

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Different carbon sources were found able to support the RABV-G expression under the control of the constitutive GAP promoter.

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Culture parameters such as oxygen supply, pH or growth rate can affect the yield and the quality of the produced RABV-G.

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The purified RABV-G was found correctly glycosylated and able to mediate trimeric oligomerization.

The commonly used host for industrial production of recombinant proteins Pichia pastoris, has been used in this work to produce the rabies virus glycoprotein (RABV-G). To allow a constitutive expression and the secretion of the expressed recombinant RABV-G, the PichiaPink™ commercialized expression vectors were modified to contain the constitutive GAP promoter and the α secretion signal sequences. Recombinant PichiaPink™ strains co-expressing the RABV-G and the protein chaperone PDI, have been then generated and screened for the best producer clone. The influence of seven carbon sources on the expression of the RABV-G, has been studied under different culture conditions in shake flask culture. An incubation temperature of 30°C under an agitation rate of 250 rpm in a filling volume of 10:1 flask/culture volume ratio were the optimal conditions for the RABV-G production in shake flask for all screened carbon sources. A bioreactor Fed batch culture has been then carried using glycerol and glucose as they were good carbon sources for cell growth and RABV-G production in shake flask scale. Cells were grown on glycerol during the batch phase then fed with glycerol or glucose defined solutions, a final RABV-G concentration of 2.7 µg/l was obtained with a specific product yield (Y_P/X) of 0.032 and 0.06 µg/g(_DCW) respectively. The use of semi-defined feeding solution enhanced the production and the Y_P/X to 12.9 µg/l and 0.135 µg/g(_DCW) respectively. However, the high cell density favored by these carbon sources resulted in oxygen limitation which influenced the glycosylation pattern of the secreted RABV-G. Alternatively, the use of sucrose as substrate for RABV-G production in large scale culture, resulted in less biomass production and a Y_P/X of 0.310 µg/g_(DCW) was obtained. A cation exchange chromatography was then used for RABV-G purification as one step method. The purified protein was correctly folded and glycosylated and able to adopt trimeric conformation. The knowledges gained through this work offer a valuable insight into the bioprocess design of RABV-G production in Pichia pastoris to obtain a correctly folded protein which can be used during an immunization proposal for subunit Rabies vaccine development.

Strains and Molecular Tools for Recombinant Protein Production in Pichia pastoris

Within the last two decades, the methylotrophic yeast Pichia pastoris (Komagataella phaffii) has become an important alternative to E. coli or mammalian cell lines for the production of recombinant proteins. Easy handling, strong promoters, and high cell density cultivations as well as the capability of posttranslational modifications are some of the major benefits of this yeast. The high secretion capacity and low level of endogenously secreted proteins further promoted the rapid development of a versatile Pichia pastoris toolbox. This chapter reviews common and new "Pichia tools" and their specific features. Special focus is given to expression strains, such as different methanol utilization, protease-deficient or glycoengineered strains, combined with application highlights. Different promoters and signal sequences are also discussed.

Customized yeast cell factories for biopharmaceuticals: from cell engineering to process scale up

The manufacture of recombinant therapeutics is a fastest-developing section of therapeutic pharmaceuticals and presently plays a significant role in disease management. Yeasts are established eukaryotic host for heterologous protein production and offer distinctive benefits in synthesising pharmaceutical recombinants. Yeasts are proficient of vigorous growth on inexpensive media, easy for gene manipulations, and are capable of adding post translational changes of eukaryotes. Saccharomyces cerevisiae is model yeast that has been applied as a main host for the manufacture of pharmaceuticals and is the major tool box for genetic studies; nevertheless, numerous other yeasts comprising Pichia pastoris, Kluyveromyces lactis, Hansenula polymorpha, and Yarrowia lipolytica have attained huge attention as non-conventional partners intended for the industrial manufacture of heterologous proteins. Here we review the advances in yeast gene manipulation tools and techniques for heterologous pharmaceutical protein synthesis. Application of secretory pathway engineering, glycosylation engineering strategies and fermentation scale-up strategies in customizing yeast cells for the synthesis of therapeutic proteins has been meticulously described.

Impact of glycerol feeding profiles on STEAP1 biosynthesis by Komagataella pastoris using a methanol-inducible promoter

Currently, the lack of reliable strategies for the diagnosis and treatment of cancer makes the identification and characterization of new therapeutic targets a pressing matter. Several studies have proposed the Six Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1) as a promising therapeutic target for prostate cancer. Although structural and functional studies may provide deeper insights on the role of STEAP1 in cancer, such techniques require high amounts of purified protein through biotechnological processes. Based on the results presented, this work proposes the application, for the first time, of a fed-batch profile to improve STEAP1 biosynthesis in mini-bioreactor Komagataella pastoris X-33 Mut⁺ methanol-induced cultures, by evaluating three glycerol feeding profiles-constant, exponential, and gradient-during the pre-induction phase. Interestingly, different glycerol feeding profiles produced differently processed STEAP1. This platform was optimized using a combination of chemical chaperones for ensuring the structural stabilization and appropriate processing of the target protein. The supplementation of culture medium with 6 % (v/v) DMSO and 1 M proline onto a gradient glycerol/constant methanol feeding promoted increased biosynthesis levels of STEAP1 and minimized aggregation events. Deglycosylation assays with peptide N-glycosidase F showed that glycerol constant feed is associated with an N-glycosylated pattern of STEAP1. The biological activity of recombinant STEAP1 was also validated, once the protein enhanced the proliferation of LNCaP and PC3 cancer cells, in comparison with non-tumoral cell cultures. This methodology could be a crucial starting point for large-scale production of active and stable conformation of recombinant human STEAP1. Thus, it could open up new strategies to unveil the structural rearrangement of STEAP1 and to better understand the biological role of the protein in cancer onset and progression.

Modeling of copy number variability in Pichia pastoris

Development of continuous biopharmaceutical manufacturing processes is an area of active research. This study considers the long-term transgene copy number stability of Pichia pastoris in continuous bioreactors. We propose a model of copy number loss that quantifies population heterogeneity. An analytical solution is derived and compared with existing experimental data. The model is then used to provide guidance for stable operating timescales. The model is extended to consider copy number dependent growth such as in the case of Zeocin supplementation. The model is also extended to analyze a continuous seeding strategy. This study is a critical step towards understanding the impact of continuous processing on the stability of Pichia pastoris and the resultant products.

Depletion of Boric Acid and Cobalt from Cultivation Media: Impact on Recombinant Protein Production with Komagataella phaffii

The REACH regulation stands for “Registration, Evaluation, Authorization and Restriction of Chemicals” and defines certain substances as harmful to human health and the environment. This urges manufacturers to adapt production processes. Boric acid and cobalt dichloride represent such harmful ingredients, but are commonly used in yeast cultivation media. The yeast Komagataella phaffii (Pichia pastoris) is an important host for heterologous protein production and compliance with the REACH regulation is desirable. Boric acid and cobalt dichloride are used as boron and cobalt sources, respectively. Boron and cobalt support growth and productivity and a number of cobalt-containing enzymes exist. Therefore, depletion of boric acid and cobalt dichloride could have various negative effects, but knowledge is currently scarce. Herein, we provide an insight into the impact of boric acid and cobalt depletion on recombinant protein production with K. phaffii and additionally show how different vessel materials affect cultivation media compositions through leaking elements. We found that boric acid could be substituted through boron leakiness from borosilicate glassware. Furthermore, depletion of boric acid and cobalt dichloride neither affected high cell density cultivation nor cell morphology and viability on methanol. However, final protein quality of three different industrially relevant enzymes was affected in various ways.

The Degree and Length of O-Glycosylation of Recombinant Proteins Produced in Pichia pastoris Depends on the Nature of the Protein and the Process Type

The methylotrophic yeast Pichia pastoris is known as an efficient host for the production of heterologous proteins. While N-linked protein glycosylation is well characterized in P. pastoris there is less knowledge of the patterns of O-glycosylation. O-glycans produced by P. pastoris consist of short linear mannose chains, which in the case of recombinant biopharmaceuticals can trigger an immune response in humans. This study aims to reveal the influence of different cultivation strategies on O-mannosylation profiles in P. pastoris. Sixteen different model proteins, produced by different P. pastoris strains, are analyzed for their O-glycosylation profile. Based on the obtained data, human serum albumin (HSA) is chosen to be produced in fast and slow growth fed batch fermentations by using common promoters, P_GAP and P_AOX1 . After purification and protein digestion, glycopeptides are analyzed by LC/ESI-MS. In the samples expressed with P_GAP it is found that the degree of glycosylation is slightly higher when a slow growth rate is used, regardless of the efficiency of the producing strain. The highest glycosylation intensity is observed in HSA produced with P_AOX1 . The results indicate that the O-glycosylation level is markedly higher when the protein is produced in a methanol-based expression system.

Development of a dual specific growth rate-based fed-batch process for production of recombinant human granulocyte colony-stimulating factor in Pichia pastoris

A number of limitations exist for production of human granulocyte colony-stimulating factor (G-CSF) in Pichia pastoris. In this study, two different specific growth rates (0.015 h^-1, 0.01 h^-1) were used sequentially in the mixed substrate feeding period during methanol induction phase to enhance the G-CSF titer in the culture broth. Necessary parameters required for implementing the feeding strategy, such as specific product yield on biomass (Y_P/X) and maintenance coefficient (m) on glycerol, methanol, and sorbitol were estimated using continuous culture technique. Using this strategy, for the same volumetric productivity, about 20% increase in protein titer was achieved over that obtained from the run carried out at a single pre-set value of 0.015 h^-1 alone. Thus, implementation of higher specific growth rate (0.015 h^-1) set during initial stages of the methanol induction phase followed by a lower specific growth rate (0.01 h^-1) helped in achieving increased protein titers.

Preventing Overflow Metabolism in Crabtree-Positive Microorganisms through On-Line Monitoring and Control of Fed-Batch Fermentations

At specific growth rates above a particular critical value, Crabtree-positive microorganisms exceed their respiratory capacity and enter diauxic growth metabolism. Excess substrate is converted reductively to an overflow metabolite, resulting in decreased biomass yield and productivity. To prevent this scenario, the cells can be cultivated in a fed-batch mode at a growth rate maintained below the critical value, µcrit. This approach entails two major challenges: accurately estimating the current specific growth rate and controlling it successfully over the course of the fermentation. In this work, the specific growth rate of S. cerevisiae and E. coli was estimated from enhanced on-line biomass concentration measurements obtained with dielectric spectroscopy and turbidity. A feedforward-feedback control scheme was implemented to maintain the specific growth rate at a setpoint below µcrit, while on-line FTIR measurements provided the early detection of the overflow metabolites. The proposed approach is in line with the principles of Bioprocess Analytical Technology (BioPAT), and provides a means to increase the productivity of Crabtree-positive microorganisms.

Improvement of a fermentation process for the production of two PfAMA1-DiCo-based malaria vaccine candidates in Pichia pastoris

Pichia pastoris is a simple and powerful expression platform that has the ability to produce a wide variety of recombinant proteins, ranging from simple peptides to complex membrane proteins. A well-established fermentation strategy is available comprising three main phases: a batch phase, followed by a glycerol fed-batch phase that increases cell density, and finally an induction phase for product expression using methanol as the inducer. We previously used this three-phase strategy at the 15-L scale to express three different AMA1-DiCo-based malaria vaccine candidates to develop a vaccine cocktail. For two candidates, we switched to a two-phase strategy lacking the intermediate glycerol fed-batch phase. The new strategy not only provided a more convenient process flow but also achieved 1.5-fold and 2.5-fold higher space-time yields for the two candidates, respectively, and simultaneously reduced the final cell mass by a factor of 1.3, thus simplifying solid–liquid separation. This strategy also reduced the quantity of host cell proteins that remained to be separated from the two vaccine candidates (by 34% and 13%, respectively), thus reducing the effort required in the subsequent purification steps. Taken together, our new fermentation strategy increased the overall fermentation performance for the production of two different AMA1-DiCo-based vaccine candidates.

Enhanced truncated-t-PA (CT-b) expression in high-cell-density fed-batch cultures of Pichia pastoris through optimization of a mixed feeding strategy by response surface methodology

Recently, Pichia pastoris has been the focal point of interest as an expression system for production of many recombinant proteins. The study and optimization of feeding strategy are of major importance to achieve maximum volumetric productivity in fed-batch cultivations. Among different feeding strategies used in P. pastoris fed-batch cultures, those trying to maintain a constant specific growth rate have usually resulted in superior productivities. The objective of the present study was to investigate and optimize the co-feeding of glycerol and methanol to attain maximum expression of t-PA in P. pastoris fed-batch cultures with constant specific growth rate. The experiments were designed by response surface methodology, considering the specific feeding rates of methanol and glycerol as independent variables. In each experiment, glycerol and methanol were fed according to a predetermined equation to maintain a constant specific growth rate. It was found that with glycerol feeding for higher specific growth rates, the inhibitory properties of glycerol are more pronounced, while the best expression level was achieved when the ratio of µ set glycerol to that of methanol was around 1.67. In all specific growth rates tested, almost a similar ratio of the specific glycerol feeding rate to that of methanol led to the maximum protein production and activity. The statistical model predicted the optimal operating conditions for µ set glycerol and that of methanol to be 0.05 and 0.03 h(-1), respectively. Applying the optimum strategy, maximum of 52 g/L biomass, 300 mg/L t-PA and 340,000 IU/mL enzyme activity were obtained.

Effect of dilution rate and methanol-glycerol mixed feeding on heterologous Rhizopus oryzae lipase production with Pichia pastoris Mut(+) phenotype in continuous culture

The induction using substrate mixtures is an operational strategy for improving the productivity of heterologous protein production with Pichia pastoris. Glycerol as a cosubstrate allows for growth at a higher specific growth rate, but also has been reported to be repressor of the expression from the AOX1 promoter. Thus, further insights about the effects of glycerol are required for designing the induction stage with mixed substrates. The production of Rhizopus oryzae lipase (ROL) was used as a model system to investigate the application of methanol-glycerol feeding mixtures in fast metabolizing methanol phenotype. Cultures were performed in a simple chemostat system and the response surface methodology was used for the evaluation of both dilution rate and methanol-glycerol feeding composition as experimental factors. Our results indicate that productivity and yield of ROL are strongly affected by dilution rate, with no interaction effect between the involved factors. Productivity showed the highest value around 0.04-0.06 h(-1) , while ROL yield decreased along the whole dilution rate range evaluated (0.03-0.1 h(-1) ). Compared to production level achieved with methanol-only feeding, the highest specific productivity was similar in mixed feeding (0.9 UA g-biomass(-1) h(-1) ), but volumetric productivity was 70% higher. Kinetic analysis showed that these results are explained by the effects of dilution rate on specific methanol uptake rate, instead of a repressor effect caused by glycerol feeding. It is concluded that despite the effect of dilution rate on ROL yield, mixed feeding strategy is a proper process option to be applied to P. pastoris Mut(+) phenotype for heterologous protein production.

Bioprocess and downstream optimization of recombinant bovine chymosin B in Pichia (Komagataella) pastoris under methanol-inducible AOXI promoter

A clone of the methylotrophic yeast Pichia pastoris strain GS115 transformed with the bovine prochymosin B gene was used to optimize the production and downstream of recombinant bovine chymosin expressed under the methanol-inducible AOXI promoter. Cell growth and recombinant chymosin production were analyzed in flask cultures containing basal salts medium with biodiesel-byproduct glycerol as the carbon source, obtaining values of biomass level and milk-clotting activity similar to those achieved with analytical glycerol. The effect of biomass level at the beginning of methanol-induction phase on cell growth and chymosin expression was evaluated, determining that a high concentration of cells at the start of such period generated an increase in the production of chymosin. The impact of the specific growth rate on chymosin expression was studied throughout the induction stage by methanol exponential feeding fermentations in a lab-scale stirred bioreactor, achieving the highest production of heterologous chymosin with a constant specific growth rate of 0.01h(-1). By gel filtration chromatography performed at a semi-preparative scale, recombinant chymosin was purified from exponential fed-batch fermentation cultures, obtaining a specific milk-clotting activity of 6400IMCU/mg of chymosin and a purity level of 95%. The effect of temperature and pH on milk-clotting activity was analyzed, establishing that the optimal temperature and pH values for the purified recombinant chymosin are 37°C and 5.5, respectively. This study reported the features of a sustainable bioprocess for the production of recombinant bovine chymosin in P. pastoris by fermentation in stirred-tank bioreactors using biodiesel-derived glycerol as a low-cost carbon source.

Strains and molecular tools for recombinant protein production in Pichia pastoris

Within the last two decades, the methylotrophic yeast Pichia pastoris has become an important alternative to E. coli or mammalian cell lines for the production of recombinant proteins. Easy handling, strong promoters, and high cell density cultivations as well as the capability of posttranslational modifications are some of the major benefits of this yeast. The high secretion capacity and low level of endogenously secreted proteins further promoted the rapid development of a versatile Pichia pastoris toolbox. This chapter reviews common and new "Pichia tools" and their specific features. Special focus is given to expression strains, such as different methanol utilization, protease-deficient or glycoengineered strains, combined with application highlights. Different promoters and signal sequences are also discussed.

Investigating the physiological response of Pichia (Komagataella) pastoris GS115 to the heterologous expression of misfolded proteins using chemostat cultures

Pichia pastoris is widely used as a host system for heterologous protein expression in both academia and industry. Production is typically accomplished by a fed-batch induction process that is known to have negative impacts on cell physiology that impose limits on both protein yields and quality. We have analysed recombinant protein production in chemostat cultures to understand the physiological responses associated with methanol-induced production of two human lysozyme variants with different degrees of misfolding by P. pastoris. Confounding variables associated with nutrient stress or growth-rate are minimised during steady-state growth in chemostats. Comparison of transcriptome-level data obtained during the non-inducing and inducing steady states identified changes in expression of only about 1 % of the genome during production of either an amyloidogenic human lysozyme variant prone to intracellular aggregation (I56T) or a misfolded but secretable variant (T70N), indicating near-complete acclimation to their production. A marked, but temporary, stress response involving both the unfolded protein response (UPR) and ER-associated degradation pathway was observed during the transient between steady states, particularly following induction of the T70N variant synthesis, and was accompanied by changes in expression of around 50 antisense transcripts. The results suggest that optimal heterologous protein production could best be achieved by a continuous process that minimises the number of methanol-induced transients experienced by the cultures. The processing of HAC1 mRNA required for the UPR was found to be constitutive in the culture conditions used, even in the absence of recombinant protein induction.

Increased production of alkaline polygalacturonate lyase in the recombinant Pichia pastoris by controlling cell concentration during continuous culture

Recombinant alkaline polygalacturonate lyase (PGL) production by recombinant Pichia pastoris GS115 was selected as a model to study as a continuous culture strategy for enhancing heterologous protein production based on controlling methanol feeding (CCCM culture) or on dual carbon source feeding (CCCD culture). Using the CCCM process with a dry cell weight of 75 g/L regulated by controlling methanol concentration in the induction media, the final PGL activity was 441.9 U/mL. The PGL productivity (Q(v)) and the average specific enzyme production rate (Q(x)) were 4.65 U mL(-1)h(-1) and 84.5 U g(-1)h(-1), an increase of 42.1% and 191.2%, respectively, over what was achieved with traditional fed-batch culture with high cell density. The control strategies also reduced proteolytic degradation by 84.1% in the fermentation broth and increased cell viability by 12.2%.

Improvement of specific growth rate of Pichia pastoris for effective porcine interferon-α production with an on-line model-based glycerol feeding strategy

Effective expression of porcine interferon-α (pIFN-α) with recombinant Pichia pastoris was conducted in a bench-scale fermentor. The influence of the glycerol feeding strategy on the specific growth rate and protein production was investigated. The traditional DO-stat feeding strategy led to very low cell growth rate resulting in low dry cell weight (DCW) of about 90 g/L during the subsequent induction phase. The previously reported Artificial Neural Network Pattern Recognition (ANNPR) model-based glycerol feeding strategy improved the cell density to 120 g DCW/L, while the specific growth rate decreased from 0.15 to 0.18 to 0.03-0.08 h(-1) during the last 10 h of the glycerol feeding stage leading to a variation of the porcine interferon-α production, as the glycerol feeding scheme had a significant effect on the induction phase. This problem was resolved by an improved ANNPR model-based feeding strategy to maintain the specific growth rate above 0.11 h(-1). With this feeding strategy, the pIFN-α concentration reached a level of 1.43 g/L, more than 1.5-fold higher than that obtained with the previously adopted feeding strategy. Our results showed that increasing the specific growth rate favored the target protein production and the glycerol feeding methods directly influenced the induction stage. Consequently, higher cell density and specific growth rate as well as effective porcine interferon-α production have been achieved by our novel glycerol feeding strategy.

Antibody expression kinetics in glycoengineered Pichia pastoris

Growth of the antibody market has fueled the development of alternative expression systems such as glycoengineered yeast. Although intact antibody expression levels in excess of 1 g L(-1) have been demonstrated in glycoengineered yeast, this is still significantly below the titers reported for antibody fragments in fungal expression systems. This study presents a simplified approach to estimate antibody secretion kinetics and oxygen uptake rate requirements as a function of growth-rate controlled by a limiting methanol feed rate in glycoengineered Pichia pastoris. The yield of biomass from methanol and the specific oxygen requirements predicted in this study compare well with values reported in the literature for wild-type P. pastoris, indicating the intrinsic nature of these yields independent of glycoengineering or the heterologous protein expressed. Specific productivity was found to be a non-linear function of specific growth rate. Based on comparison with relationships between specific growth rate and specific productivity reported in the literature this correlation seems empirical in nature and cannot be established a priori. These correlations were then used in a simple mass balance based model to predict the cultivation performance of carbon limited cultivations under oxygen transfer limited conditions to indicate the usefulness of this approach to predict large scale performance and aid in process development.

Insecticidal activity of recombinant avidin produced in yeast

An expression construct encoding chicken (Gallus gallus) avidin was assembled from amplified fragments of genomic DNA. Recombinant, functional avidin was produced in Pichia pastoris, with yields of up to 80 mg/l of culture supernatant. The recombinant avidin had similar insecticidal activity to egg white avidin when assayed against larvae of a lepidopteran crop pest, cabbage moth (Mamestra brassicae), causing >90% reduction in growth and 100% mortality when fed in optimised diets at levels of 1.5 microM and 15 microM (100 ppm and 1000 ppm wet weight of recombinant protein). The recombinant protein was also highly toxic to a hemipteran pest, the pea aphid (Acyrthosiphon pisum), when fed in liquid artificial diet, causing 100% mortality after 4 days when present at concentrations > or = 3.8 microM (0.25 mg/ml, 250 ppm). Mortality was dose-dependent, with an estimated LC(50) of 2.1 microM. Toxicity to A. pisum was prevented by biotin supplementation of diet. In contrast, avidin had no significant effects on the survival of cereal aphid (Sitobion avenae) at concentrations up to 30 microM in liquid diet. Analysis of genomic DNA showed that symbionts from both aphid species lack the ability to synthesise biotin de novo. Cereal aphids appear to be less sensitive to recombinant avidin in the diet through proteolysis of the ingested protein, which would allow recovery of bound biotin.

Fed-batch methanol feeding strategy for recombinant protein production by Pichia pastoris in the presence of co-substrate sorbitol

Batch-wise sorbitol addition as a co-substrate at the induction phase of methanol fed-batch fermentation by Pichia pastoris (Mut(+)) was proposed as a beneficial recombinant protein production strategy and the metabolic responses to methanol feeding rate in the presence of sorbitol was systematically investigated. Adding sorbitol batch-wise to the medium provided the following advantages over growth on methanol alone: (a) eliminating the long lag-phase for the cells and reaching 'high cell density production' at t = 24 h of the process (C(X) = 70 g CDW/l); (b) achieving 1.8-fold higher recombinant human erythropoietin (rHuEPO) (at t = 18 h); (c) reducing specific protease production 1.2-fold; (d) eliminating the lactic acid build-up period; (e) lowering the oxygen uptake rate two-fold; and (f) obtaining 1.4-fold higher overall yield coefficients. The maximum specific alcohol oxidase activity was not affected in the presence of sorbitol, and it was observed that sorbitol and methanol were utilized simultaneously. Thus, in the presence of sorbitol, 130 mg/l rHuEPO was produced at t = 24 h, compared to 80 mg/l rHuEPO (t = 24 h) on methanol alone. This work demonstrates not only the ease and efficiency of incorporating sorbitol to fermentations by Mut(+) strains of P. pastoris for the production of any bio-product, but also provides new insights into the metabolism of the methylotrophic yeast P. pastoris.

A quantitative analysis of the benefits of mixed feeds of sorbitol and methanol for the production of recombinant avidin with Pichia pastoris

The advantages of mixed feeds of sorbitol and methanol for the production of recombinant proteins with Pichia pastoris were analyzed quantitatively. The influence of the methanol-sorbitol ratio in the feed medium was investigated on growth stoichiometry and recombinant protein productivity with a P. pastoris Mut(+) strain secreting avidin by performing a transient nutrient gradient in continuous cultivation at a dilution rate of 0.03h(-1). Results showed that mixed feeds of sorbitol and methanol instead of methanol as sole carbon source can improve the productivity in recombinant avidin due to increased biomass yields during mixed substrate growth. The highest volumetric avidin productivity was achieved at a methanol fraction of 43%C-molC-mol(-1) in the feed medium: the volumetric avidin productivity was 1.3-fold higher than during chemostat culture on methanol. The heat production and the oxygen consumption rates were reduced by about 38% for a given dry cell weight concentration at this methanol fraction, features which are very useful for high cell density cultures. Results were in good agreement with a high cell density fed-batch culture performed with a mixed feed of 43% methanol and 57% sorbitol C-molC-mol(-1) at a specific growth rate of 0.03h(-1) during the induction phase. Moreover, it was confirmed that sorbitol accumulation in the culture medium does not affect recombinant avidin productivity, which can especially be advantageous during large-scale cultures where transient substrate accumulation can result from imperfect mixing.