Enhancing the efficiency of recombinant hepatitis B surface antigen production in Pichia pastoris by employing continuous fermentation

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.

The outlooks and key challenges in renewable biomass feedstock utilization for value-added platform chemical via bioprocesses

The conversion of renewable biomass feedstock into value-added products via bioprocessing platforms has become attractive because of environmental and health concerns. Process performance and cost competitiveness are major factors in the bioprocess design to produce desirable products from biomass feedstock. Proper pretreatment allows delignification and hemicellulose removal from the liquid fraction, allowing cellulose to be readily hydrolyzed to monomeric sugars. Several industrial products are produced via sugar fermentation using either naturally isolated or genetically modified microbes. Microbial platforms play an important role in the synthesis of several products, including drop-in chemicals, as-in products, and novel compounds. The key elements in developing a fermentation platform are medium formulation, sterilization, and active cells for inoculation. Downstream bioproduct recovery may seem like a straightforward chemical process, but is more complex, wherein cost competitiveness versus recovery performance becomes a challenge. This review summarizes the prospects for utilizing renewable biomass for bioprocessing.

Therapeutic proteins: developments, progress, challenges, and future perspectives

Proteins are considered magic molecules due to their enormous applications in the health sector. Over the past few decades, therapeutic proteins have emerged as a promising treatment option for various diseases, particularly cancer, cardiovascular disease, diabetes, and others. The formulation of protein-based therapies is a major area of research, however, a few factors still hinder the large-scale production of these therapeutic products, such as stability, heterogenicity, immunogenicity, high cost of production, etc. This review provides comprehensive information on various sources and production of therapeutic proteins. The review also summarizes the challenges currently faced by scientists while developing protein-based therapeutics, along with possible solutions. It can be concluded that these proteins can be used in combination with small molecular drugs to give synergistic benefits in the future.

Development of a continuous fermentation process for the production of recombinant uricase enzyme by Pichia pastoris

Recent studies in the biopharmaceutical industry have shown an increase in the productivity and production efficiency of recombinant proteins by continuous culture. In this research, a new upstream fermentation process was developed for the production of recombinant uricase in the methylotrophic yeast Pichia pastoris. Expression of recombinant protein in this system is under the control of the AOX1 promoter and therefore requires methanol as an inducing agent and carbon/energy source. Considering the biphasic growth characteristics of conventional fed-batch fermentation, physical separation of the growth and induction stages for better control of the continuous fermentation process resulted in higher dry-cell weight (DCW) and enhanced recombinant urate oxidase activity. The DCW and recombinant uricase activity enzyme for fed-batch fermentation were 79 g/L and 6.8 u/mL. During the continuous process, in the growth fermenter at a constant dilution rate of 0.025 h-1 , DCW increased to 88.39 g/L. In the induction fermenter, at methanol feeding rates of 30, 60, and 80 mL/h, a recombinant uricase activity was 4.13, 7.2, and 0 u/mL, respectively. The optimum methanol feeding regime in continuous fermentation resulted in a 4.5-fold improvement in productivity compared with fed-batch fermentation from 0.04 u/mL/h (0.0017 mg/mL/h) to 0.18 u/mL/h (0.0078 mg/mL/h).

Methanol-based biomanufacturing of fuels and chemicals using native and synthetic methylotrophs

Methanol has recently gained significant attention as a potential carbon substrate for the production of fuels and chemicals, owing to its high degree of reduction, abundance, and low price. Native methylotrophic yeasts and bacteria have been investigated for the production of fuels and chemicals. Alternatively, synthetic methylotrophic strains are also being developed by reconstructing methanol utilization pathways in model microorganisms, such as Escherichia coli. Owing to the complex metabolic pathways, limited availability of genetic tools, and methanol/formaldehyde toxicity, the high-level production of target products for industrial applications are still under development to satisfy commercial feasibility. This article reviews the production of biofuels and chemicals by native and synthetic methylotrophic microorganisms. It also highlights the advantages and limitations of both types of methylotrophs and provides an overview of ways to improve their efficiency for the production of fuels and chemicals from methanol.

Challenges and progress towards industrial recombinant protein production in yeasts: A review

Recombinant proteins (RP) are widely used as biopharmaceuticals, industrial enzymes, or sustainable food source. Yeasts, with their ability to produce complex proteins through a broad variety of cheap carbon sources, have emerged as promising eukaryotic production hosts. As such, the prevalence of yeasts as favourable production organisms in commercial RP production is expected to increase. Yet, with the selection of a robust production host on the one hand, successful scale-up is dependent on a thorough understanding of the challenging environment and limitations of large-scale bioreactors on the other hand. In the present work, several prominent yeast species, including Saccharomyces cerevisiae, Pichia pastoris, Yarrowia lipolytica, Kluyveromyces lactis and Kluyveromyces marxianus are reviewed for their current state and performance in commercial RP production. Thereafter, the impact of principal process control parameters, including dissolved oxygen, pH, substrate concentration, and temperature, on large-scale RP production are discussed. Finally, technical challenges of process scale-up are identified. To that end, process intensification strategies to enhance industrial feasibility are summarized, specifically highlighting fermentation strategies to ensure sufficient cooling capacity, overcome oxygen limitation, and increase protein quality and productivity. As such, this review aims to contribute to the pursuit of sustainable yeast-based RP production.

P AOX1 expression in mixed-substrate continuous cultures of Komagataella phaffii (Pichia pastoris) is completely determined by methanol consumption regardless of the secondary carbon source

The expression of recombinant proteins by the AOX1 promoter of Komagataella phaffii is typically induced by adding methanol to the cultivation medium. Since growth on methanol imposes a high oxygen demand, the medium is often supplemented with an additional secondary carbon source which serves to reduce the consumption of methanol, and hence, oxygen. Early research recommended the use of glycerol as the secondary carbon source, but more recent studies recommend the use of sorbitol because glycerol represses P AOX1 expression. To assess the validity of this recommendation, we measured the steady state concentrations of biomass, residual methanol, and LacZ expressed from P AOX1 over a wide range of dilution rates (0.02-0.20 h-1) in continuous cultures of the Mut+ strain fed with methanol + glycerol (repressing) and methanol + sorbitol (non-repressing). We find that under these conditions, the specific P AOX1 expression rate (measured as either specific LacZ productivity or specific AOX productivity) is completely determined by the specific methanol consumption rate regardless of the type (repressing/non-repressing) of the secondary carbon source. In both cultures, the specific P AOX1 expression rate is proportional to the specific methanol consumption rate, provided that the latter is below 0.15 g/(gdw-h); beyond this threshold consumption rate, the specific P AOX1 expression rate of both cultures saturates to the same value. Analysis of the data in the literature shows that the same phenomenon also occurs in continuous cultures of Escherichia coli fed with mixtures of lactose plus repressing/non-repressing carbon sources. The specific P lac expression rate is completely determined by the specific lactose consumption rate, regardless of the type of secondary carbon source, glycerol or glucose.

A review of yeast: High cell-density culture, molecular mechanisms of stress response and tolerance during fermentation

Yeast is widely used in the fermentation industry, and the major challenges in fermentation production system are high capital cost and low reaction rate. High cell-density culture is an effective method to increase the volumetric productivity of the fermentation process, thus making the fermentation process faster and more robust. During fermentation, yeast is subjected to various environmental stresses, including osmotic, ethanol, oxidation, and heat stress. To cope with these stresses, yeast cells need appropriate adaptive responses to acquire stress tolerances to prevent stress-induced cell damage. Since a single stressor can trigger multiple effects, both specific and nonspecific effects, general and specific stress responses are required to achieve comprehensive protection of cells. Since all these stresses disrupt protein structure, the upregulation of heat shock proteins and trehalose genes is induced when yeast cells are exposed to stress. A better understanding of the research status of yeast HCDC and its underlying response mechanism to various stresses during fermentation is essential for designing effective culture control strategies and improving the fermentation efficiency and stress resistance of yeast.

How far have we explored fungi to fight cancer?

The use of fungal cultures have been well documented in human history. Although its used in healthcare, like penicillin and statins, have saved countless of lives, but there is still no fungal products that are specifically indicated for cancers. Research into fungal-derived materials to curb cancers in the recent decades have made a considerable progress in terms of drug delivery vehicles, anticancer active ingredients and cancer immunotherapy. Various parts of the organisms have successfully been exploited to achieve specific tasks. Apart from the identification of novel anticancer compound from fungi, its native capsular structure can also be used as drug cargo to achieve higher oral bioavailability. This review summarises the anticancer potential of fungal-derived materials, highlighting the role of capsular polysaccharides, proteins, and other structures in variety of innovative utilities to fit the current pharmaceutical technology. Many bioactive compounds isolated from fungi have also been formulated into nanoparticles to achieve greater anticancer activity. The progress of fungal compounds and their analogues in clinical trials is also highlighted. In addition, the potential of various fungal species to be developed for anticancer immunotherapy are also discussed.

Quantitative assessment of LPS-HBsAg interaction by introducing a novel application of immunoaffinity chromatography

Lipopolysaccharide (LPS), as a stubborn contamination, should be monitored and kept in an acceptable level during the pharmaceutical production process. Recombinant hepatitis B surface antigen (r-HBsAg) is one of the recombinant biological products, which is probable to suffer from extrinsic endotoxin due to its long and complex production process. This research aims to assess the potential interaction between LPS and r-HBsAg by recruiting immunoaffinity chromatography (IAC) as a novel tool to quantify the interaction. Molecular modeling was performed on the HBsAg molecule to theoretically predict its potential binding and interaction sites. Then dynamic light scattering (DLS) analysis was implemented on HBsAg, LPS, and mixtures of them to reveal the interaction. The virus-like particle (VLP) structure of HBsAg and the ribbon-like structure of LPS were visualized by transmission electron microscopy (TEM). Finally, the interaction was quantified by applying various LPS/HBsAg ratios ranging from 1.67 to 120 EU/dose in the IAC. Consequently, the LPS/HBsAg ratios in the eluate were measured from 1.67 to a maximum of 92.5 EU/dose. The results indicated that 77 to 100% of total LPS interacted with HBsAg by an inverse relationship to the incubated LPS concentration. The findings implied that the introduced procedure is remarkably practical in the quantification of LPS interaction with a target recombinant protein.

Green Process: Improved Semi-Continuous Fermentation of Pichia pastoris Based on the Principle of Vitality Cell Separation

The large-scale fermentation of Pichia pastoris for recombinant protein production would be time consuming and produce a large amount of waste yeast. Here we introduce a novel semi-continuous fermentation process for P. pastoris GS115 that can separate vitality cells from broth and recycle the cells to produce high-secretory recombinant pectate lyase. It is based on differences in cell sedimentation coefficients with the formation of salt bridges between metal ions and various cell states. Compared to batch-fed cultivation and general semi-continuous culture, the novel process has significant advantages, such as consuming fewer resources, taking less time, and producing less waste yeast. Sedimentation with the addition of Fe3+ metal ions consumed 14.8 ± 0.0% glycerol, 97.8 ± 1.3% methanol, 55.0 ± 0.9 inorganic salts, 81.5 ± 0.0% time cost, and 77.0 ± 0.1% waste yeast versus batch-fed cultivation to produce an equal amount of protein; in addition, the cost of solid-liquid separation was lower for cells in the collected fermentation broth. The process is economically and environmentally efficient for producing recombinant proteins.

Enhancing the recombinant protein productivity of Yarrowia lipolytica using insitu fibrous bed bioreactor

In this study, the ability of Yarrowia lipolytica to produce the recombinant lipase CalB from Candida antarctica, used as a model protein has been compared across different bioreactor processes using glycerol, a byproduct from the biodiesel industry as the main carbon source. Batch, pulsed fed-batch (PFB), and continuous fed-batch (CFB) strategies were first compared using classical stirred tank (STR) bioreactors in terms of biomass production, carbon source uptake, and lipase production. Additionally, an in situ fibrous bed bioreactor (isFBB) was developed using sugarcane bagasse as a cell immobilization support. The maximum lipase titer achieved using the isFBB culture mode was 38%, 33%, and 49% higher than those obtained using the batch, PFB, and CFB cultures, respectively. The lipase productivity in isFBB mode (142U/mL/h) was 1.4-fold higher than that obtained using batch free cell cultures. These results highlight that isFBB is an efficient technology for the production of recombinant enzymes.

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.

Continuous Cultivation as a Tool Toward the Rational Bioprocess Development With Pichia Pastoris Cell Factory

The methylotrophic yeast Pichia pastoris (Komagataella phaffii) is currently considered one of the most promising hosts for recombinant protein production (RPP) and metabolites due to the availability of several tools to efficiently regulate the recombinant expression, its ability to perform eukaryotic post-translational modifications and to secrete the product in the extracellular media. The challenge of improving the bioprocess efficiency can be faced from two main approaches: the strain engineering, which includes enhancements in the recombinant expression regulation as well as overcoming potential cell capacity bottlenecks; and the bioprocess engineering, focused on the development of rational-based efficient operational strategies. Understanding the effect of strain and operational improvements in bioprocess efficiency requires to attain a robust knowledge about the metabolic and physiological changes triggered into the cells. For this purpose, a number of studies have revealed chemostat cultures to provide a robust tool for accurate, reliable, and reproducible bioprocess characterization. It should involve the determination of key specific rates, productivities, and yields for different C and N sources, as well as optimizing media formulation and operating conditions. Furthermore, studies along the different levels of systems biology are usually performed also in chemostat cultures. Transcriptomic, proteomic and metabolic flux analysis, using different techniques like differential target gene expression, protein description and ¹³C-based metabolic flux analysis, are widely described as valued examples in the literature. In this scenario, the main advantage of a continuous operation relies on the quality of the homogeneous samples obtained under steady-state conditions, where both the metabolic and physiological status of the cells remain unaltered in an all-encompassing picture of the cell environment. This contribution aims to provide the state of the art of the different approaches that allow the design of rational strain and bioprocess engineering improvements in Pichia pastoris toward optimizing bioprocesses based on the results obtained in chemostat cultures. Interestingly, continuous cultivation is also currently emerging as an alternative operational mode in industrial biotechnology for implementing continuous process operations.

Transcriptomic Analysis of Pichia pastoris (Komagataella phaffii) GS115 During Heterologous Protein Production Using a High-Cell-Density Fed-Batch Cultivation Strategy

Pichia pastoris (Komagataella phaffii) is a methylotrophic yeast that is widely used in industry as a host system for heterologous protein expression. Heterologous gene expression is typically facilitated by strongly inducible promoters derived from methanol utilization genes or constitutive glycolytic promoters. However, protein production is usually accomplished by a fed-batch induction process, which is known to negatively affect cell physiology, resulting in limited protein yields and quality. To assess how yields of exogenous proteins can be increased and to further understand the physiological response of P. pastoris to the carbon conversion of glycerol and methanol, as well as the continuous induction of methanol, we analyzed recombinant protein production in a 10,000-L fed-batch culture. Furthermore, we investigated gene expression during the yeast cell culture phase, glycerol feed phase, glycerol-methanol mixture feed (GM) phase, and at different time points following methanol induction using RNA-Seq. We report that the addition of the GM phase may help to alleviate the adverse effects of methanol addition (alone) on P. pastoris cells. Secondly, enhanced upregulation of the mitogen-activated protein kinase (MAPK) signaling pathway was observed in P. pastoris following methanol induction. The MAPK signaling pathway may be related to P. pastoris cell growth and may regulate the alcohol oxidase1 (AOX1) promoter via regulatory factors activated by methanol-mediated stimulation. Thirdly, the unfolded protein response (UPR) and ER-associated degradation (ERAD) pathways were not significantly upregulated during the methanol induction period. These results imply that the presence of unfolded or misfolded phytase protein did not represent a serious problem in our study. Finally, the upregulation of the autophagy pathway during the methanol induction phase may be related to the degradation of damaged peroxisomes but not to the production of phytase. This work describes the metabolic characteristics of P. pastoris during heterologous protein production under high-cell-density fed-batch cultivation. We believe that the results of this study will aid further in-depth studies of P. pastoris heterologous protein expression, regulation, and secretory mechanisms.

Magnetic Immobilization of Pichia pastoris Cells for the Production of Recombinant Human Serum Albumin

Magnetic immobilization as a novel technique was used to immobilize recombinant Pichia pastoris (GS115 Albumin) cells to produce human serum albumin (HSA). In this regard, magnetic nanoparticles (MNPs) coated with amino propyl triethoxy silane (APTES) were synthesized. P. pastoris cells were decorated with MNPs via nonspecific interactions. Decorated cells were magneto-responsible and easily harvested by applying an external magnetic field. The efficiency of magnetic immobilization (E_i) for cell removal was in direct relation with the MNP concentration and time of exposure to the magnetic field. By increasing the nanoparticles concentration, cells were harvested in a shorter period. Complete cell removal (E_i ≈ 100) was achieved in ≥0.5 mg/mL of MNPs in just 30 s. HSA is produced in an extremely high cell density (OD ~20) and it is the first time that magnetic immobilization was successfully employed for harvesting such a thick cell suspension. After 5 days of induction the cells, which were immobilized with 0.25 to 1 mg/mL of nanoparticles, showed an increased potency for recombinant HSA production. The largest increase in HSA production (38.1%) was achieved in the cells that were immobilized with 0.5 mg/mL of nanoparticles. These results can be considered as a novel approach for further developments in the P. pastoris-based system.

Recent Developments in Bioprocessing of Recombinant Proteins: Expression Hosts and Process Development

Infectious diseases, along with cancers, are among the main causes of death among humans worldwide. The production of therapeutic proteins for treating diseases at large scale for millions of individuals is one of the essential needs of mankind. Recent progress in the area of recombinant DNA technologies has paved the way to producing recombinant proteins that can be used as therapeutics, vaccines, and diagnostic reagents. Recombinant proteins for these applications are mainly produced using prokaryotic and eukaryotic expression host systems such as mammalian cells, bacteria, yeast, insect cells, and transgenic plants at laboratory scale as well as in large-scale settings. The development of efficient bioprocessing strategies is crucial for industrial production of recombinant proteins of therapeutic and prophylactic importance. Recently, advances have been made in the various areas of bioprocessing and are being utilized to develop effective processes for producing recombinant proteins. These include the use of high-throughput devices for effective bioprocess optimization and of disposable systems, continuous upstream processing, continuous chromatography, integrated continuous bioprocessing, Quality by Design, and process analytical technologies to achieve quality product with higher yield. This review summarizes recent developments in the bioprocessing of recombinant proteins, including in various expression systems, bioprocess development, and the upstream and downstream processing of recombinant proteins.

Application of hydrocyclone for separation of Pichia pastoris produced r-HBsAg from fermentation culture: impact of concentration and pressure on hydrocyclone performance

Separation of biomass from culture media by centrifugation and then washing the biomass are mandatory steps in the fermentation process of recombinant Pichia pastoris expressed HBsAg intracellularly. Biomass has to be washed many times to eliminate the culture media residues thoroughly. In this study, we tried to develop the hydrocyclone as an alternative method for separation of biomass from fermentation culture, an attractive replacement for centrifugation processes. The advantages of using hydrocyclone in biomass separation could be summarized in its suitability for continuous separation and its low risk of contamination. To evaluate the performance of hydrocyclone, concentration ratio in underflow to feed stream, capacity, and centrifugal force by considering three parameters of pressure drop, concentration, and the type of hydrocyclone were investigated. Using three level factorial design a concentration ratio equation was developed, with the correlation coefficient R² = 0.977 ensured the good fitness of the predicted data with the experimental results. In optimal conditions, maximum concentration ratio was 1.246, for flow rate 13.5 LPM and C-force equal to 1276.11 at maximum pressure drop (3 bar) and minimum concentration (0.5% w/w) in hydrocyclone 1. Herein, two different hydrocyclones with the cylindrical diameters of 19 mm and 21 mm were used for separating the yeast cells.

Accurate and cost-effective prediction of HBsAg titer in industrial scale fermentation process of recombinant Pichia pastoris by using neural network based soft sensor

In the current work, the attempt was made to apply best-fitted artificial neural network (ANN) architecture and the respective training process for predicting final titer of hepatitis B surface antigen (HBsAg), produced intracellularly by recombinant Pichia pastoris Mut⁺ in the commercial scale. For this purpose, in large-scale fed-batch fermentation, using methanol for HBsAg induction and cell growth, three parameters of average specific growth rate, biomass yield, and dry biomass concentration-in the definite integral form with respect to fermentation time-were selected as input vectors; the final concentration of HBsAg was selected for the ANN output. Used dataset consists of 38 runs from previous batches; feed-forward ANN 3:5:1 with training algorithm of backpropagation based on a Bayesian regularization was trained and tested with a high degree of accuracy. Implementing the verified ANN for predicting the HBsAg titer of the five new fermentation runs, excluded from the dataset, in the full-scale production, the coefficient of regression and root-mean-square error were found to be 0.969299 and 2.716774, respectively. These results suggest that this verified soft sensor could be an excellent alternative for the current relatively expensive and time-intensive analytical techniques such as enzyme-linked immunosorbent assay in the biopharmaceutical industry.

Application of recurrent neural network for online prediction of cell density of recombinant Pichia pastoris producing HBsAg

Artificial neural networking (ANN) seems to be a promising soft sensor for implementing current approaches of quality by design (QbD) and process analytical technologies (PAT) in the biopharmaceutical industry. In this study, we aimed to implement best-fitted ANN architecture for online prediction of the biomass amount of recombinant Pichia pastoris (P. pastoris) - expressing intracellular hepatitis B surface antigen (HBsAg) - during the fed-batch fermentation process using methanol as a sole carbon source. For this purpose, at the induction phase of methanol fed-batch fermentation, carbon evolution rate (CER), dissolved oxygen (DO), and methanol feed rate were selected as input vectors and total wet cell weight (WCW) was considered as output vector for the ANN. The obtained results indicated that after training recurrent ANN with data sets of four fed-batch runs, this toolbox could predict the WCW of the next fed-batch fermentation process at each specified time point with high accuracy. The R-squared and root-mean-square error between actual and predicted values were found to be 0.9985 and 13.73, respectively. This verified toolbox could have major importance in the biopharmaceutical industry since recombinant P. pastoris is widely used for the large-scale production of HBsAg.

Integration of size-exclusion chromatography and ultracentrifugation for purification of recombinant hepatitis B surface antigen: An alternative method for immunoaffinity chromatography

In purification process of recombinant hepatitis B surface antigen (rHBsAg), immunoaffinity chromatography (IAF) is one of the most important and effective steps in rHBsAg purification. However, the buffer composition and the interaction of ligands-rHBsAg often lead to disassembly, deformation, and clumping of a portion of these virus-like particles (VLPs). Besides, the expensive media, variable biospecific ligand density and the possibility of product contamination are other reported drawbacks of using IAF which makes the production process of rHBsAg more challenging. This study investigated the possibility of substituting IAF with purification methods of size-exclusion chromatography (SEC) and ultracentrifugation. In the SEC, the efficacy of rHBsAg purification was examined by four different media in which Toyopearl HW 65S resin demonstrated the best results. By integrating Toyopearl HW 65S resin - with a bed height of 51 cm - and ultracentrifugation process at 47,000 rpm for 48 hr, 95% of protein impurities were removed. Compared to the IAF in rHBsAg production, the purified sample contained a higher percentage of multimeric rHBsAg particles without any noticeable monomer and aggregate forms. The result of this study indicates that the proposed integrated system could be an efficient mild purification alternative for conventional IAF.