Safety evaluation of a lipase enzyme preparation, expressed in Pichia pastoris, intended for use in the degumming of edible vegetable oil

Recent progress on heterologous protein production in methylotrophic yeast systems

Recombinant protein production technology is widely applied to the manufacture of biologics used as drug substances and industrial proteins such as recombinant enzymes and bioactive proteins. Various heterologous protein production systems have been developed using prokaryotic and eukaryotic hosts. Especially methylotrophic yeast in eukaryotic hosts is suggested to be particularly valuable because such systems have the following advantages: protein secretion into culture broth, eukaryotic quality control systems, a post-translational modification system, rapid growth, and established recombinant DNA tools and technologies such as strong promoters, effective selection markers, and gene knock-in and -out systems. Many methylotrophic yeasts such as the genera Candida, Ogataea, and Komagataella have been studied since methylotrophic yeast was first isolated in 1969. The methanol-consumption-related genes in methylotrophic yeast are strongly and strictly regulated under methanol-containing conditions. The well-regulated gene expression systems under the methanol-inducible gene promoter lead to the potential application of heterologous protein production in methylotrophic yeast. In this review, we describe the recent progress of heterologous protein production technology in methylotrophic yeast and introduce Ogataea minuta as an alternative production host as a substitute for K. phaffii and O. polymorpha.

Multiplex Marker-Less Genome Integration in Pichia pastoris Using CRISPR/Cas9

Pichia pastoris is known for its excellent protein expression ability. As an industrial methyl nutritional yeast, it can effectively utilize methanol as the sole carbon source, serving as a potential platform for C1 biotransformation. Unfortunately, the lack of synthetic biology tools in P. pastoris limits its broad applications, particularly when multigene pathways should be manipulated. Here, the CRISPR/Cas9 system is established to efficiently integrate multiple heterologous genes to construct P. pastoris cell factories. In this protocol, with the 2,3-butanediol (BDO) biosynthetic pathway as a representative example, the procedures to construct P. pastoris cell factories are detailed using the established CRISPR-based multiplex genome integration toolkit, including donor plasmid construction, competent cell preparation and transformation, and transformant verification. The application of the CRISPR toolkit is demonstrated by the construction of engineered P. pastoris for converting methanol to BDO. This lays the foundation for the construction of P. pastoris cell factories harboring multi-gene biosynthetic pathways for the production of high-value compounds.

Co-Formulation of Recombinant Porcine IL-18 Enhances the Onset of Immune Response in a New Lawsonia intracellularis Vaccine

Pig is one of the most consumed meats worldwide. One of the main conditions for pig production is Porcine Enteropathy caused by Lawsonia intracellularis. Among the effects of this disease is chronic mild diarrhea, which affects the weight gain of pigs, generating economic losses. Vaccines available to prevent this condition do not have the desired effect, but this limitation can be overcome using adjuvants. Pro-inflammatory cytokines, such as interleukin 18 (IL-18), can improve an immune response, reducing the immune window of protection. In this study, recombinant porcine IL-18 was produced and expressed in Escherichia coli and Pichia pastoris. The protein's biological activity was assessed in vitro and in vivo, and we determined that the P. pastoris protein had better immunostimulatory activity. A vaccine candidate against L. intracellularis, formulated with and without IL-18, was used to determine the pigs' cellular and humoral immune responses. Animals injected with the candidate vaccine co-formulated with IL-18 showed a significant increase of Th1 immune response markers and an earlier increase of antibodies than those vaccinated without the cytokine. This suggests that IL-18 acts as an immunostimulant and vaccine adjuvant to boost the immune response against the antigens, reducing the therapeutic window of recombinant protein-based vaccines.

The Safety of Soy Leghemoglobin Protein Preparation Derived from Pichia pastoris Expressing a Soy Leghemoglobin Gene from Glycine max: In Vitro and In Vivo Studies

Soy leghemoglobin (LegH) protein derived from soy (Glycine max) produced in Pichia pastoris (reclassified as Komagataella phaffii) as LegH Prep is a novel food ingredient that provides meat-like flavor and aroma to plant-derived food products. The safety of LegH Prep has been previously assessed in a battery of in vivo and in vitro testing and found no adverse effects under the conditions tested. In this new work, we present the results of new in vivo and in vitro tests evaluating the safety of LegH Prep. LegH Prep was nonmutagenic in a bacterial reverse mutation assay and nonclastogenic in an in vitro micronucleus assay in human lymphocytes. Systemic toxicity was evaluated in the 90 day dietary study in male and female Sprague-Dawley® rats that included a 28 day recovery period. The study resulted in no animal deaths associated with the administration of LegH Prep at the highest dose (90,000 ppm). There were no significant adverse clinical or physical changes attributed to LegH Prep administration, and no observed adverse effects on either male or female rats over the course of the 28 day recovery phase study. The new 90 day dietary toxicity study established a no observed adverse effect level (NOAEL) of 4798.3 and 5761.5 mg/kg/day, the maximum level tested for male and female rats, respectively. Thus, the results of the studies demonstrate that under the conditions tested, LegH Prep is not toxic for consumption in meat analog products.

Expression and biochemical characterization of a Bacillus subtilis catalase in Pichia pastoris X-33

Catalase, which catalyzes the decomposition of H₂O₂ to H₂O and O₂, is widely used to reduce H₂O₂ in industrial applications, such as in food processing, textile dyeing and wastewater treatment. In this study, the catalase (KatA) from Bacillus subtilis was cloned and expressed in the yeast Pichia pastoris X-33. The effect of the promoter in the expression plasmid on the activity level of the secreted KatA protein was also studied. First, the gene encoding KatA was cloned and inserted into a plasmid containing an inducible alcohol oxidase 1 promoter (pAOX1) or a constitutive glyceraldehyde-3-phosphate dehydrogenase promoter (pGAP). The recombinant plasmids were validated by colony PCR and sequencing and then linearized and transformed into the yeast P. pastoris X-33 for expression. With the promoter pAOX1, the maximum yield of KatA in the culture medium reached 338.8 ± 9.6 U/mL in 2 days of shake flask cultivation, which was approximately 2.1-fold greater than the maximum yield obtained with the promoter pGAP. The expressed KatA was then purified from the culture medium by anion exchange chromatography, and its specific activity was determined to be 14826.58 U/mg. Finally, the purified KatA exhibited optimum activity at 25 °C and pH 11.0. Its K_m for hydrogen peroxide was 10.9 ± 0.5 mM, and its k_cat/K_m was 5788.1 ± 25.6 s^-1 mM^-1. Through the work presented in this article, we have therefore demonstrated efficient expression and purification of KatA in P. pastoris, which might be advantageous for scaling up the production of KatA for use in a variety of biotechnological applications.

Medium optimization for enhanced production of recombinant lignin peroxidase in Pichia pastoris

OBJECTIVES

Different cultivation conditions and parameters were evaluated to improve the production and secretion of a recombinant Phanerochaete chrysosporium lipH8 gene in Komagataella phaffii (Pichia pastoris).

RESULTS

The recombinant lipH8 gene with its native secretion signal was successfully cloned and expressed in Komagataella phaffii (Pichia pastoris) under the control of the alcohol oxidase 1 promoter (P_AOX1). The results revealed that co-feeding with sorbitol and methanol increased rLiP secretion by 5.9-fold compared to the control conditions. The addition of 1 mM FeSO₄ increased LiP activity a further 6.0-fold during the induction phase. Moreover, the combination of several optimal conditions and parameters yielded an extracellular rLiP activity of 20.05 U l^-1, which is more than ten-fold higher relative to standard growth conditions (BMM10 medium, pH 6 and 30 °C).

CONCLUSION

Extracellular activity of a recombinant LiP expressed in P. pastoris increased more than ten-fold when co-feeding sorbitol and methanol as carbon sources, together with urea as nitrogen source, FeSO₄ supplementation, lower pH and lower cultivation temperature.

Safety evaluation of oubli fruit sweet protein (brazzein) derived from Komagataella phaffii, intended for use as a sweetener in food and beverages

Naturally sweet proteins have no glycemic effect and offer a fundamentally new approach to sweetness and health for individuals seeking to reduce their added sugar intake. However, unlike many commercial sweeteners, little research has been performed on the potential safety implications of adding these uniquely sweet proteins to food and beverages. In this study, a naturally sweet protein found in the West African Oubli plant ( Pentadiplandra brazzeana), referred to as Oubli fruit sweet protein or brazzein, was expressed in Komagataella phaffii (formerly Pichia pastoris) and produced via precision fermentation, and a safety and risk assessment was undertaken for its use as a sweetener in food and beverages. Potential consumption levels of brazzein were estimated to be 3 mg/kg body weight/day based on the National Health and Nutrition Examination Survey. The safety of brazzein derived from K. phaffii was evaluated through in silico allergenicity, in vitro genotoxicity (reverse mutation and mammalian micronucleus assays), and a 90-day dietary oral toxicity study in rats. There was no indication of allergenicity in the in silico analyses. Brazzein was non-genotoxic in the in vitro assays and showed no adverse effects in the 90-day oral toxicity study up to the highest dose tested, where the no-observed-adverse-effect level (NOAEL) was 978 and 985 mg/kg body weight/day in males and females, respectively. The totality of evidence in the in silico allergenicity, in vitro genotoxicity, and 90-day dietary toxicity studies demonstrates that brazzein derived from K. phaffii is considered safe for use as a sweetener in food and beverages.

Generation of 4-vinylguaiacol through a novel high-affinity ferulic acid decarboxylase to obtain smoke flavours without carcinogenic contaminants

Traditional smoke flavours bear the risk of containing a multitude of contaminating carcinogenic side-products. Enzymatic decarboxylation of ferulic acid released from agro-industrial side-streams by ferulic acid esterases (FAE) enables the sustainable generation of pure, food grade 4-vinylguaiacol (4-VG), the impact compound of smoke flavour. The first basidiomycetous ferulic acid decarboxylase (FAD) was isolated from Schizophyllum commune (ScoFAD) and heterologously produced by Komagataella phaffii. It showed a molecular mass of 21 kDa, catalytic optima at pH 5.5 and 35°C, and a sequence identity of 63.6% to its next relative, a FAD from the ascomycete Cordyceps farinosa. The ScoFAD exhibited a high affinity to its only known substrate ferulic acid (FA) of 0.16 mmol L^-1 and a turnover number of 750 s^-1. The resulting catalytic efficiency k_cat K_M^-1 of 4,779 L s^-1 mmol^-1 exceeded the next best known enzyme by more than a factor of 50. Immobilised on AminoLink Plus Agarose, ScoFAD maintained its activity for several days. The combination with FAEs and agro-industrial side-streams paves the way for a new generation of sustainable, clean, and safe smoke flavours.

Expression of multidrug transporter P-glycoprotein in Pichia pastoris affects the host's methanol metabolism

Pichia pastoris KM71H (MutS ) is an efficient producer of hard-to-express proteins such as the membrane protein P-glycoprotein (Pgp), an ATP-powered efflux pump which is expressed properly, but at very low concentration, using the conventional induction strategy. Evaluation of different induction strategies indicated that it was possible to increase Pgp expression by inducing the culture with 20% media containing 2.5% methanol. By quantifying methanol, formaldehyde, hydrogen peroxide and formate, and by measuring alcohol oxidase, catalase, formaldehyde dehydrogenase, formate dehydrogenase, malate dehydrogenase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenases, it was possible to correlate Pgp expression to the induction strategy. Inducing the culture by adding methanol with fresh media was associated with decreases in formaldehyde and hydrogen peroxide, and increases in formaldehyde dehydrogenase, formate dehydrogenase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenases. At these conditions, Pgp expression was 1400-fold higher, an indication that Pgp expression is affected by increases in formaldehyde and hydrogen peroxide. It is possible that Pgp is responsible for this behaviour, since the increased metabolite concentrations and decreased enzymatic activities were not observed when parental Pichia was subjected to the same growth conditions. This report adds information on methanol metabolism during expression of Pgp from P. pastoris MutS strain and suggests an expression procedure for hard-to-express proteins from P. pastoris.

Induction of EGFP expression in Pichia pastoris during co-culture with human endothelial cell line

While Pichia pastoris has been developed into a versatile recombinant protein expression system, there are only few studies that have investigated the efficacious use of this yeast with human cells. In this study, we demonstrated that P. pastoris can be cultured under mammalian cell culture conditions and co-cultured with human endothelial cells. Co-cultures did not affect endothelial cell morphology or viability. Additionally, P. pastoris was induced to express enhanced green fluorescence protein when co-cultured with human endothelial cell line EA.hy926 under mammalian cell culture conditions. Our study provides data to support the use of P. pastoris as a vehicle for direct delivery of recombinant proteins to mammalian cells during co-culture.

Yeast-secreted, dried and food-admixed monomeric IgA prevents gastrointestinal infection in a piglet model

A scalably manufacturable oral antibody technology that can interfere with gastrointestinal (GI) targets is needed. Contrary to the complex native secretory IgA, we achieve this using a single-gene encoded monomeric-IgA-like antibody, composed of camelid VHH fused to IgA Fc (mVHH-IgA). This can be produced in soybean seeds or secreted from Pichia pastoris yeast, freeze-or spray-dried, and when delivered in food prevents enterotoxigenic Escherichia coli (F4-ETEC) infection in piglets.

Next generation designer virus-like particle vaccines for dengue

INTRODUCTION

A safe and efficacious vaccine for dengue continues to be an unmet public health need. The recent licensing of a dengue vaccine (Dengvaxia) developed by Sanofi has brought to the fore the safety issue of vaccine-induced infection enhancement.

AREAS COVERED

This article focuses on two new yeast-produced tetravalent dengue envelope domain III-displaying virus-like particulate vaccine candidates reported in early 2018 and reviews the rationale underlying their design, and pre-clinical data which suggest that these may offer promising alternate options.

EXPERT COMMENTARY

These are the only vaccine candidates so far to have demonstrated the induction of primarily serotype-specific neutralizing antibodies to all dengue virus serotypes in experimental animals. Interestingly, these antibodies lack infection-enhancing potential when evaluated using the AG129 mouse model.

Established and Upcoming Yeast Expression Systems

Yeast was the first microorganism used by mankind for biotransformation of feedstock that laid the foundations of industrial biotechnology. Long historical use, vast amount of data, and experience paved the way for Saccharomyces cerevisiae as a first yeast cell factory, and still it is an important expression platform as being the production host for several large volume products. Continuing special needs of each targeted product and different requirements of bioprocess operations have led to identification of different yeast expression systems. Modern bioprocess engineering and advances in omics technology, i.e., genomics, transcriptomics, proteomics, secretomics, and interactomics, allow the design of novel genetic tools with fine-tuned characteristics to be used for research and industrial applications. This chapter focuses on established and upcoming yeast expression platforms that have exceptional characteristics, such as the ability to utilize a broad range of carbon sources or remarkable resistance to various stress conditions. Besides the conventional yeast S. cerevisiae, established yeast expression systems including the methylotrophic yeasts Pichia pastoris and Hansenula polymorpha, the dimorphic yeasts Arxula adeninivorans and Yarrowia lipolytica, the lactose-utilizing yeast Kluyveromyces lactis, the fission yeast Schizosaccharomyces pombe, and upcoming yeast platforms, namely, Kluyveromyces marxianus, Candida utilis, and Zygosaccharomyces bailii, are compiled with special emphasis on their genetic toolbox for recombinant protein production.

Efficient Production of Recombinant Protegrin-1 From Pichia pastoris, and Its Antimicrobial and in vitro Cell Migration Activity

Protegrin (PG) belongs to the antimicrobial peptide cathelicidin family. To date, five protegrin sequences have been identified in pigs, PG-1 to PG-5. Of these, PG-1 exhibits potent antimicrobial activity against a broad range of antibiotic-resistant microorganisms as well as viruses. However, the other potential role(s) of PG beyond antimicrobial has largely been unexplored. The aim of this study was to use nonpathogenic yeast Pichia pastoris to express antimicrobially active recombinant protegrin (rPG-1). Additionally, the effect of PG-1 on cell migration and proliferation was also examined in vitro using pig intestinal epithelial cells as a model. Highest level of rPG-1 (104 ± 11 μg/mL) was detected at 24 h in fermentation culture medium. Similar to rPG-1, 0.8 ± 0.10 g/L of proform PG-1 (rProPG-1) and 0.2 ± 0.02 g/L of the PG-1 cathelin domain (rCath) was detected in fermentation culture medium. Resulting recombinant PG-1 and cleaved rProPG-1 exerted antimicrobial activity against Escherichia coli DH5α at the same level as chemically synthesized PG-1. Enhanced cell migration was observed (p < 0.05) in groups treated with rProPG-1, rCath, and rPG-1 compared to the control. Furthermore, rPG-1 was stable at temperatures ranging from 25°C to 80°C. In summary, biologically active recombinant protegrin in its pro-, cathelin-, and mature- forms were successfully expressed in P. pastoris suggesting potential feasibility for future therapeutic applications.

Safety Evaluation of Soy Leghemoglobin Protein Preparation Derived From Pichia pastoris, Intended for Use as a Flavor Catalyst in Plant-Based Meat

The leghemoglobin protein (LegH) from soy ( Glycine max) expressed in Pichia pastoris (LegH preparation, LegH Prep) imparts a meat-like flavor profile onto plant-based food products. The safety of LegH Prep was evaluated through a series of in vitro and in vivo tests. The genotoxic potential of LegH Prep was assessed using the bacterial reverse mutation assay (Ames test) and the in vitro chromosome aberration test. LegH Prep was nonmutagenic and nonclastogenic in each test, respectively. Systemic toxicity was assessed in a 28-day dietary study in male and female Sprague Dawley rats. There were no mortalities associated with the administration of LegH Prep. There were no clinical observations, body weight, ophthalmological, clinical pathology, or histopathological changes attributable to LegH Prep administration. There were no observed effects on male reproduction in this study, but the suggestion of a potential estrous cycle distribution effect in female rats prompted a second comprehensive 28-day dietary study in female Sprague Dawley rats. This study demonstrated that female reproductive parameters were comparable between rats treated with LegH Prep and concurrent control rats. These studies establish a no observed adverse effect level of 750 mg/kg/d LegH, which is over 100 times greater than the 90th percentile estimated daily intake. Collectively, the results of the studies presented raise no issues of toxicological concern with regard to LegH Prep under the conditions tested.

Recycling of a selectable marker with a self-excisable plasmid in Pichia pastoris

Pichia pastoris is a widely used heterologous protein production workhorse. However, with its multiple genetic modifications to solve bottlenecks for heterologous protein productivity, P. pastoris lacks selectable markers. Existing selectable marker recycling plasmids have drawbacks (e.g., slow growth and conditional lethality). Here, zeocin-resistance marker recycling vectors were constructed using the Cre/loxP recombination system. The vectors were used to (i) knock in heterologous phytase, xylanase and lipase expression cassettes, (ii) increase the phytase, xylanase and lipase gene copy number to 13, 5, and 5, respectively, with vector introduction and (iii) engineer the secretion pathway by co-overexpressing secretion helper factors (Sly1p and Sec1p) without introducing selectable markers, giving a phytase field of 0.833 g/L. The vectors allow selectable marker recycling and would be a useful tool to engineer P. pastoris for high heterologous protein productivity.

Immunization with Tc52 or its amino terminal domain adjuvanted with c-di-AMP induces Th17+Th1 specific immune responses and confers protection against Trypanosoma cruzi

The development of new adjuvants enables fine modulation of the elicited immune responses. Ideally, the use of one or more adjuvants should result in the induction of a protective immune response against the specific pathogen. We have evaluated the immune response and protection against Trypanosoma cruzi infection in mice vaccinated with recombinant Tc52 or its N- and C-terminal domains (NTc52 and CTc52) adjuvanted either with the STING (Stimulator of Interferon Genes) agonist cyclic di-AMP (c-di-AMP), a pegylated derivative of α-galactosylceramide (αGC-PEG), or oligodeoxynucleotides containing unmethylated CpG motifs (ODN-CpG). All groups immunized with the recombinant proteins plus adjuvant: Tc52+c-di-AMP, NTc52+c-di-AMP, CTc52+c-di-AMP, NTc52+c-di-AMP+αGC-PEG, NTc52+CpG, developed significantly higher anti-Tc52 IgG titers than controls. Groups immunized with c-di-AMP and Tc52, NTc52 or CTc52 showed the highest Tc52-specific IgA titers in nasal lavages. All groups immunized with the recombinant proteins plus adjuvant developed a strong specific cellular immune response in splenocytes and lymph node cells with significant differences for groups immunized with c-di-AMP and Tc52, NTc52 or CTc52. These groups also showed high levels of Tc52-specific IL-17 and IFN-γ producing cells, while NTc52+CpG group only showed significant difference with control in IFN-γ producing cells. Groups immunized with c-di-AMP and Tc52, NTc52 or CTc52 developed predominantly a Th17 and Th1immune response, whereas for NTc52+CpG it was a dominant Th1 response. It was previously described that αGC-PEG inhibits Th17 differentiation by activating NKT cells. Thus, in this work we have also included a group immunized with both adjuvants (NTc52+c-di-AMP+αGC-PEG) with the aim to modulate the Th17 response induced by c-di-AMP. This group showed a significant reduction in the number of Tc52-specific IL-17 producing splenocytes, as compared to the group NTc52+c-di-AMP, which has in turn correlated with a reduction in protection against infection. These results suggest that the Th17 immune response developed after immunizing with NTc52+c-di-AMP could have a protective role against T. cruzi infection. Groups NTc52+c-di-AMP, Tc52+c-di-AMP and NTc52PB, were the ones that showed better protection against infection with lower parasitemia and weight loss, and higher survival.

Chagas disease is a parasitic disease caused by a protozoan parasite (Trypanosoma cruzi) which has a complex life cycle including insect vector and mammalians. In Latin America, 7–10 million people are infected, 100 million people are at risk of infection, and about 56,000 new infection cases and 12,000 deaths are registered annually. Migration spread the geographic distribution of the disease to North America and Europe. The infection in humans has an initial acute stage followed by a chronic stage where up to 30% of patients develop cardiac alterations and 10% develop digestive, neurological or mixed alterations. The acute infection is hardly detected and there is not drug to treat the chronic infection. Thus, there is an urgent need for prophylactic and therapeutic vaccines development. Several attempts to find a vaccine antigen has been made and the protein Tc52 is a good candidate. In a vaccine composition, as important as the antigen is the adjuvants, which are substances able to increase, improve or modified the immune response. This research provides information about the immune response and protection against Trypanosoma cruzi infection elicited by Tc52 or portions of this molecule using different adjuvants.

Dynamic genome-scale metabolic modeling of the yeast Pichia pastoris

BACKGROUND

Pichia pastoris shows physiological advantages in producing recombinant proteins, compared to other commonly used cell factories. This yeast is mostly grown in dynamic cultivation systems, where the cell's environment is continuously changing and many variables influence process productivity. In this context, a model capable of explaining and predicting cell behavior for the rational design of bioprocesses is highly desirable. Currently, there are five genome-scale metabolic reconstructions of P. pastoris which have been used to predict extracellular cell behavior in stationary conditions.

RESULTS

In this work, we assembled a dynamic genome-scale metabolic model for glucose-limited, aerobic cultivations of Pichia pastoris. Starting from an initial model structure for batch and fed-batch cultures, we performed pre/post regression diagnostics to ensure that model parameters were identifiable, significant and sensitive. Once identified, the non-relevant ones were iteratively fixed until a priori robust modeling structures were found for each type of cultivation. Next, the robustness of these reduced structures was confirmed by calibrating the model with new datasets, where no sensitivity, identifiability or significance problems appeared in their parameters. Afterwards, the model was validated for the prediction of batch and fed-batch dynamics in the studied conditions. Lastly, the model was employed as a case study to analyze the metabolic flux distribution of a fed-batch culture and to unravel genetic and process engineering strategies to improve the production of recombinant Human Serum Albumin (HSA). Simulation of single knock-outs indicated that deviation of carbon towards cysteine and tryptophan formation improves HSA production. The deletion of methylene tetrahydrofolate dehydrogenase could increase the HSA volumetric productivity by 630%. Moreover, given specific bioprocess limitations and strain characteristics, the model suggests that implementation of a decreasing specific growth rate during the feed phase of a fed-batch culture results in a 25% increase of the volumetric productivity of the protein.

CONCLUSION

In this work, we formulated a dynamic genome scale metabolic model of Pichia pastoris that yields realistic metabolic flux distributions throughout dynamic cultivations. The model can be calibrated with experimental data to rationally propose genetic and process engineering strategies to improve the performance of a P. pastoris strain of interest.

Recent advances of molecular toolbox construction expand Pichia pastoris in synthetic biology applications

Pichia pastoris: (reclassified as Komagataella phaffii), a methylotrophic yeast strain has been widely used for heterologous protein production because of its unique advantages, such as readily achievable high-density fermentation, tractable genetic modifications and typical eukaryotic post-translational modifications. More recently, P. pastoris as a metabolic pathway engineering platform has also gained much attention. In this mini-review, we addressed recent advances of molecular toolboxes, including synthetic promoters, signal peptides, and genome engineering tools that established for P. pastoris. Furthermore, the applications of P. pastoris towards synthetic biology were also discussed and prospected especially in the context of genome-scale metabolic pathway analysis.

Beyond bread and beer: whole cell protein extracts from baker's yeast as a bulk source for 3D cell culture matrices

Here, we present a novel approach to form hydrogels from yeast whole cell protein. Countless hydrogels are available for sophisticated research, but their fabrication is often difficult to reproduce, with the gels being complicated to handle or simply too expensive. The yeast hydrogels presented here are polymerized using a four-armed, amine reactive crosslinker and show a high chemical and thermal resistance. The free water content was determined by measuring swelling ratios for different protein concentrations, and in a freeze-drying approach, pore sizes of up to 100 μm in the gel could be created without destabilizing the 3D network. Elasticity was proofed to be adjustable with the help of atomic force microscopy by merely changing the amount of used protein. Furthermore, the material was tested for possible cell culture applications; diffusion rates in the network are high enough for sufficient supply of human breast cancer cells and adenocarcinomic human alveolar basal epithelial cells with nutrition, and cells showed high viabilities when tested for compatibility with the material. Furthermore, hydrogels could be functionalized with RGD peptide and the optimal concentration for sufficient cell adhesion was determined to be 150 μM. Given that yeast protein is one of the cheapest and easiest available protein sources and that hydrogels are extremely easy to handle, the developed material has highly promising potential for both sophisticated cell culture techniques as well as for larger scale industrial applications.

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.

Protein expression in Pichia pastoris: recent achievements and perspectives for heterologous protein production

Pichia pastoris is an established protein expression host mainly applied for the production of biopharmaceuticals and industrial enzymes. This methylotrophic yeast is a distinguished production system for its growth to very high cell densities, for the available strong and tightly regulated promoters, and for the options to produce gram amounts of recombinant protein per litre of culture both intracellularly and in secretory fashion. However, not every protein of interest is produced in or secreted by P. pastoris to such high titres. Frequently, protein yields are clearly lower, particularly if complex proteins are expressed that are hetero-oligomers, membrane-attached or prone to proteolytic degradation. The last few years have been particularly fruitful because of numerous activities in improving the expression of such complex proteins with a focus on either protein engineering or on engineering the protein expression host P. pastoris. This review refers to established tools in protein expression in P. pastoris and highlights novel developments in the areas of expression vector design, host strain engineering and screening for high-level expression strains. Breakthroughs in membrane protein expression are discussed alongside numerous commercial applications of P. pastoris derived proteins.

Cloning, expression and optimized production in a bioreactor of bovine chymosin B in Pichia (Komagataella) pastoris under AOX1 promoter

The codon sequence optimized bovine prochymosin B gene was cloned under the control of the alcohol oxidase 1 promoter (AOX1) in the vector pPIC9K and integrated into the genome of the methylotrophic yeast Pichia (Komagataella) pastoris (P. pastoris) strain GS115. A transformant clone that showed resistance to over 4 mg G418/ml and displayed the highest milk-clotting activity was selected. Cell growth and recombinant bovine chymosin production were optimized in flask cultures during methanol induction phase achieving the highest coagulant activity with low pH values, a temperature of 25°C and with the addition of sorbitol and ascorbic acid at the beginning of this period. The scaling up of the fermentation process to lab-scale stirred bioreactor using optimized conditions, allowed to reach 240 g DCW/L of biomass level and 96 IMCU/ml of milk-clotting activity. The enzyme activity corresponded to 53 mg/L of recombinant bovine chymosin production after 120 h of methanol induction. Western blot analysis of the culture supernatant showed that recombinant chymosin did not suffer degradation during the protein production phase. By a procedure that included high performance gel filtration chromatography and 3 kDa fast ultrafiltration, the recombinant bovine chymosin was purified and concentrated from fermentation cultures, generating a specific activity of 800 IMCU/Total Abs(280 nm) and a total activity recovery of 56%. This study indicated that P. pastoris is a suitable expression system for bioreactor based fed-batch fermentation process for the efficient production of recombinant bovine chymosin under methanol-inducible AOX1 promoter.

Phospholipases in food industry: a review

Mammal, plant, and mainly microbial phospholipases are continuously being studied, experimented, and some of them are even commercially available at industrial scale for food industry. This is because the use of phospholipases in the production of specific foods leads to attractive advantages, such as yield improvement, energy saving, higher efficiency, improved properties, or better quality of the final product. Furthermore, biocatalysis approaches in the food industry are of current interest as non-pollutant and cleaner technologies. The present chapter reviews the most representative examples of the use of phospholipases in food industry, namely edible oils, dairy, and baking products, emulsifying agents, as well as the current trend to the development of novel molecular species of phospholipids with added-value characteristics.

Impact of food processing on the safety assessment for proteins introduced into biotechnology-derived soybean and corn crops

The food safety assessment of new agricultural crop varieties developed through biotechnology includes evaluation of the proteins introduced to impart desired traits. Safety assessments can include dietary risk assessments similar to those performed for chemicals intentionally, or inadvertently added to foods. For chemicals, it is assumed they are not degraded during processing of the crop into food fractions. For introduced proteins, the situation can be different. Proteins are highly dependent on physical forces in their environment to maintain appropriate three-dimensional structure that supports functional activity. Food crops such as corn and soy are not consumed raw but are extensively processed into various food fractions. During processing, proteins in corn and soy are subjected to harsh environmental conditions that drastically change the physical forces leading to denaturation and loss of protein function. These conditions include thermal processing, changes in pH, reducing agents, mechanical shearing etc. Studies have shown that processing of introduced proteins such as enzymes that impart herbicide tolerance or proteins that control insect pests leads to a complete loss of functional activity. Thus, dietary exposure to functionally active proteins in processed food products can be negligible and below levels of any safety concerns.

A novel extracellular phospholipase C purified from a marine bacterium, Pseudoalteromonas sp. J937

Marine bacterial isolates were screened for phospholipase C (PLC) activity on PCY agar plates containing phosphatidylcholine (PC) as substrate. The strain that showed the highest activity on a PCY screening agar plate and a thin-layer chromatography was identified as a strain of Pseudoalteromonas and subsequently designated Pseudoalteromonas sp. J937. The extracellular PLC of the strain J937 was purified to a specific activity of 33 U mg(-1) protein by serial ion exchange and gel filtration column chromatography. It had a molecular mass of 32 kDa estimated by SDS-PAGE. The optimal pH and temperature of the enzyme were about pH 8 and 45 degrees C, respectively. The PLC hydrolyzed phosphatidylethanolamine as well as PC but not other glycerophospholipids. Its activity was enhanced by 150% with Ca2+ (200 mM) and by 180% with Na+ (500 mM), suggesting that the purified PLC is a marine-type enzyme.

Phospholipases and their industrial applications

Phospholipids are present in all living organisms. They are a major component of all biological membranes, along with glycolipids and cholesterol. Enzymes aimed at modifying phospholipids, namely, phospholipases, are consequently widespread in nature, playing very diverse roles from aggression in snake venom to signal transduction and digestion in humans. In this review, we give a general overview of phospholipases A1, A2, C and D from a sequence and structural perspective and their industrial application. The use of phospholipases in industrial processes has grown hand-in-hand with our ability to clone and express the genes in microbial hosts with commercially attractive amounts. Further, the use in industrial processes is increasing by optimizing the enzymes by protein engineering. Here, we give a perspective on the work done to date to express phospholipases in heterologous hosts and the efforts to optimize them by protein engineering. We will draw attention to the industrial processes where phospholipases play a key role and show how the use of a phospholipase for oil degumming leads to substantial environmental benefits. This illustrates a very general trend: the use of enzymes as an alternative to chemical processes to make products often provides a cleaner solution for the industrial processes. In a world with great demands on non-polluting, energy saving technical solutions--white biotechnology is a strong alternative.