Tobacco BY-2 Media Component Optimization for a Cost-Efficient Recombinant Protein Production

VALORIZATION OF SHOPPING CENTER SIDE- AND WASTE STREAMS WITH PLANT CELL CULTURE TECHNOLOGY - PROSPECTS AND COST REDUCTION

Upcycling potential of side-streams and waste material, originating from a shopping center were studied as a feedstock for plant cell cultures of arctic bramble (Rubus arcticus L.), barley (Hordeum vulgare L.) and tobacco BY-2 (Nicotiana tabacum L.). Soft drink waste mix, orange peels, expired bread, spent coffee grounds, and brewer's spent grain, were used in cultivation experiments to supplement sucrose in the basic growth medium. Artificial urine was included to represent a future scenario, where also human urine could be used as a circular feedstock along improvement in purification technologies allowing removal of microbes and toxic molecules. Diluted artificial urine was used to replace elemental macronutrients e.g., ammonium, phosphate, and sulphate in the culture medium. Soft drink waste mix and artificial urine contributed to the highest biomass accumulation of the tested side streams. Culture medium composition optimization, exploiting combination of soft drink waste mix and artificial urine, was conducted with design of experiments software. The optimized culture medium contributed to notable culture medium cost reductions of 55%, 33% and 45% for arctic bramble, tobacco BY-2 and barley cell lines, respectively, without compromising the biomass yield. However, modified culture medium induced some changes in the amino acid composition of arctic bramble plant cell biomass, e.g., increased asparagine and decreased arginine, alanine and tyrosine contents. Thus, attention should be paid to the amino acid composition in further studies. Our findings confirm the potential of upcycling side streams and replacing costly growth medium components with so far unutilized resources.

Unlocking the full potential of plant cell-based production for valuable proteins: Challenges and innovative strategies

Plant cell-based bioproduction systems offer a promising platform for the sustainable production of valuable proteins as they provide distinctive advantages over mammalian cell culture and whole plant cultivation. However, significant technical challenges remain, including low productivity, altered efficacy of plant-derived proteins, along with issues in culture process development, such as cell clumping, genetic instability, and difficulties with cryopreservation. To date, the full production potential of this platform remains largely untapped. This review addresses these critical challenges and proposes innovative strategies to unlock the full potential of the production platform. Rather than simply revisiting past advancements or summarizing current progress, it proposes forward-thinking solutions with a particular emphasis on cellular engineering. Key strategies include designing novel protein partners to enhance recombinant protein accumulation and functionality, employing precise gene integration techniques in genome to enhance transgene transcription, implementing cutting-edge methods for screening and maintaining elite cell lines to mitigate genetic instability, and leveraging genome editing tools for cellular engineering to develop new plant cell lines optimized for bioproduction. A key focus is on cell wall engineering to develop cellulose- or pectin-deficient cell lines, facilitating modifications to the morphology of existing plant cell lines. By exploring these innovative approaches, this review aims to foster innovative thinking and inspire future research in plant cell-based bioproduction.

A comprehensive review of recombinant technology in the food industry: Exploring expression systems, application, and future challenges

Biotechnology has significantly advanced the production of recombinant proteins (RPs). This review examines the latest advancements in protein production technologies, including CRISPR, genetic engineering, vector integration, and fermentation, and their implications for the food industry. This review delineates the merits and shortcomings of prevailing host systems for RP production, underscoring molecular and process strategies pivotal for amplifying yields and purity. It traverses the spectrum of RP applications, challenges, and burgeoning trends, highlighting the imperative of employing robust hosts and cutting-edge genetic engineering to secure high-quality, high-yield outputs while circumventing protein aggregation and ensuring correct folding for enhanced activity. Recombinant technology has paved the way for the food industry to produce alternative proteins like leghemoglobin and cytokines, along with enzyme preparations such as proteases and lipases, and to modify microbial pathways for synthesizing beneficial compounds, including pigments, terpenes, flavonoids, and functional sugars. However, scaling microbial production to industrial scales presents economic, efficiency, and environmental challenges that demand innovative solutions, including high-throughput screening and CRISPR/Cas9 systems, to bolster protein yield and quality. Although recombinant technology holds much promise, it must navigate high costs and scalability to satisfy the escalating global demand for RPs in therapeutics and food. The variability in ethical and regulatory hurdles across regions further complicates market acceptance, underscoring an urgent need for robust regulatory frameworks for genetically modified organisms. These frameworks are essential for safeguarding the production process, ensuring product safety, and upholding the efficacy of RPs in industrial applications.

From Division to Death: Metabolomic Analysis of Nicotiana tabacum BY-2 Cells Reveals the Complexity of Life in Batch Culture

Tobacco BY-2 cell culture is one of the most widely used models in plant biology. The main advantage of BY-2 suspension cultures is the synchronization of cell development and the appearance of polar elongation. In batch culture, BY-2 cells passed through the lag, proliferation, elongation, and stationary phases. During this process, the composition of the growth medium changed dramatically. Sucrose was rapidly eliminated; hexose first accumulated and then depleted. The medium's pH initially decreased and then rose with aging. As a result of the crosstalk between the internal and external stimuli, cells pass through complicated systemic rearrangements, which cause metabolomic alterations. The early stages were characterized by high levels of amino acids and sterols, which could be interpreted as the result of synthetic activity. The most intense rearrangements occurred between the proliferation and active elongation stages, including repression of amino acid accumulation and up-regulation of sugar metabolism. Later stages were distinguished by higher levels of secondary metabolites, which may be a non-specific response to deteriorating conditions. Senescence was followed by some increase in fatty acids and sterols as well as amino acids, and probably led to self-destructive processes. A correlation analysis revealed relationships between metabolites' covariation, their biochemical ratio, and the growth phase.

Production and characterization of novel Anti-HIV Fc-fusion proteins in plant-based systems: Nicotiana benthamiana & tobacco BY-2 cell suspension

Multifunctional anti-HIV Fc-fusion proteins aim to tackle HIV efficiently through multiple modes of action. Although results have been promising, these recombinant proteins are hard to produce. This study explored the production and characterization of anti-HIV Fc-fusion proteins in plant-based systems, specifically Nicotiana benthamiana plants and tobacco BY-2 cell suspension. Fc-fusion protein expression in plants was optimized by incorporating codon optimization, ER retention signals, and hydrophobin fusion elements. Successful transient protein expression was achieved in N. benthamiana, with notable improvements in expression levels achieved through N-terminal hydrophobin fusion and ER retention signals. Stable expression in tobacco BY-2 resulted in varying accumulation levels being at highest 2.2.mg/g DW. The inclusion of hydrophobin significantly enhanced accumulation, providing potential benefits for downstream processing. Mass spectrometry analysis confirmed the presence of the ER retention signal and of N-glycans. Functional characterization revealed strong binding to CD64 and CD16a receptors, the latter being important for antibody-dependent cellular cytotoxicity (ADCC). Interaction with HIV antigens indicated potential neutralization capabilities. In conclusion, this research highlights the potential of plant-based systems for producing functional anti-HIV Fc-fusion proteins, offering a promising avenue for the development of these novel HIV therapies.

Enhanced efficacy of glycoengineered rice cell-produced trastuzumab

For several decades, a plant-based expression system has been proposed as an alternative platform for the production of biopharmaceuticals including therapeutic monoclonal antibodies (mAbs), but the immunogenicity concerns associated with plant-specific N-glycans attached in plant-based biopharmaceuticals has not been completely solved. To eliminate all plant-specific N-glycan structure, eight genes involved in plant-specific N-glycosylation were mutated in rice (Oryza sativa) using the CRISPR/Cas9 system. The glycoengineered cell lines, PhytoRice®, contained a predominant GnGn (G0) glycoform. The gene for codon-optimized trastuzumab (TMab) was then introduced into PhytoRice® through Agrobacterium co-cultivation. Selected cell lines were suspension cultured, and TMab secreted from cells was purified from the cultured media. The amino acid sequence of the TMab produced by PhytoRice® (P-TMab) was identical to that of TMab. The inhibitory effect of P-TMab on the proliferation of the BT-474 cancer cell line was significantly enhanced at concentrations above 1 μg/mL (****P < 0.0001). P-TMab bound to a FcγRIIIa variant, FcγRIIIa-F158, more than 2.7 times more effectively than TMab. The ADCC efficacy of P-TMab against Jurkat cells was 2.6 times higher than that of TMab in an in vitro ADCC assay. Furthermore, P-TMab demonstrated efficient tumour uptake with less liver uptake compared to TMab in a xenograft assay using the BT-474 mouse model. These results suggest that the glycoengineered PhytoRice® could be an alternative platform for mAb production compared to current CHO cells, and P-TMab has a novel and enhanced efficacy compared to TMab.

Plant Heterotrophic Cultures: No Food, No Growth

Plant cells are capable of uptaking exogenous organic substances. This inherited trait allows the development of heterotrophic cell cultures in various plants. The most common of them are Nicotiana tabacum and Arabidopsis thaliana. Plant cells are widely used in academic studies and as factories for valuable substance production. The repertoire of compounds supporting the heterotrophic growth of plant cells is limited. The best growth of cultures is ensured by oligosaccharides and their cleavage products. Primarily, these are sucrose, raffinose, glucose and fructose. Other molecules such as glycerol, carbonic acids, starch, and mannitol have the ability to support growth occasionally, or in combination with another substrate. Culture growth is accompanied by processes of specialization, such as elongation growth. This determines the pattern of the carbon budget. Culture ageing is closely linked to substrate depletion, changes in medium composition, and cell physiological rearrangements. A lack of substrate leads to starvation, which results in a decrease in physiological activity and the mobilization of resources, and finally in the loss of viability. The cause of the instability of cultivated cells may be the non-optimal metabolism under cultural conditions or the insufficiency of internal regulation.

C-Terminal Domain Controls Protein Quality and Secretion of Spider Silk in Tobacco Cells

The remarkable mechanical strength and extensibility of spider dragline silk spidroins are attributed to the major ampullate silk proteins (MaSp). Although fragmented MaSp molecules have been extensively produced in various heterologous expression platforms for biotechnological applications, complete MaSp molecules are required to achieve instinctive spinning of spidroin fibers from aqueous solutions. Here, a plant cell-based expression platform for extracellular production of the entire MaSp2 protein is developed, which exhibits remarkable self-assembly properties to form spider silk nanofibrils. The engineered transgenic Bright-yellow 2 (BY-2) cell lines overexpressing recombinant secretory MaSp2 proteins yield 0.6-1.3  µg L-1 at 22 days post-inoculation, which is four times higher than those of cytosolic expressions. However, only 10-15% of these secretory MaSp2 proteins are discharged into the culture media. Surprisingly, expression of functional domain-truncated MaSp2 proteins lacking the C-terminal domain in transgenic BY-2 cells increases recombinant protein secretion incredibly, from 0.9 to 2.8 mg L-1 per day within 7 days. These findings demonstrate significant improvement in the extracellular production of recombinant biopolymers such as spider silk spidroins using plant cells. In addition, the results reveal the regulatory roles of the C-terminal domain of MaSp2 proteins in controlling their protein quality and secretion.

Simulation and optimization of nutrient uptake and biomass formation using a multi-parameter Monod-type model of tobacco BY-2 cell suspension cultures in a stirred-tank bioreactor

Introduction

Tobacco (Nicotiana tabacum) cv Bright Yellow-2 (BY-2) cell suspension cultures enable the rapid production of complex protein-based biopharmaceuticals but currently achieve low volumetric productivity due to slow biomass formation. The biomass yield can be improved with tailored media, which can be designed either by laborious trial-and-error experiments or systematic, rational design using mechanistic models, linking nutrient consumption and biomass formation.

Methods

Here we developed an iterative experiment-modeling-optimization workflow to gradually refine such a model and its predictions, based on collected data concerning BY-2 cell macronutrient consumption (sucrose, ammonium, nitrate and phosphate) and biomass formation.

Results and discussion

The biomass formation was well predicted by an unstructured segregated mechanistic Monod-type model as long as the nutrient concentrations did not approach zero (we omitted phosphate, which was completely depleted). Multi-criteria optimization for sucrose and biomass formation indicated the best tradeoff (in a Paretian sense) between maximum biomass yield and minimum process time by reducing the initial sucrose concentration, whereas the inoculation biomass could be increased to maximize the biomass yield or minimize the process time, which we confirmed in calibration experiments. The model became inaccurate at biomass densities > 8 g L-1 dry mass when sucrose was almost depleted. We compensated for this limitation by including glucose and fructose as sucrose hydrolysis products in the model. The remaining offset between the simulation and experimental data might be resolved by including intracellular pools of sucrose, ammonium, nitrate and phosphate. Overall, we demonstrated that iterative models can be used to systematically optimize conditions for bioreactor-based processes.

Intracellular trafficking and glycosylation of hydroxyproline-O-glycosylation module in tobacco BY-2 cells is dependent on medium composition and transcriptome analysis

Expression of recombinant proteins in plant cells with a "designer" hydroxyproline (Hyp)-O-glycosylated peptide (HypGP), such as tandem repeats of a "Ser-Pro" motif, has been shown to boost the secreted protein yields. However, dramatic secretion and Hyp-O-glycosylation of HypGP-tagged proteins can only be achieved when the plant cells were grown in nitrogen-deficient SH medium. Only trace amounts of secreted fusion protein were detected in MS medium. This study aims to gain a deeper understanding of the possible mechanism underlying these results by examining the intracellular trafficking and Hyp-O-glycosylation of enhanced green fluorescent protein (EGFP) fused with a (SP)32 tag, consisting of 32 repeats of a "Ser-Pro" motif, in tobacco BY-2 cells. When cells were grown in MS medium, the (SP)32-EGFP formed protein body-like aggregate and was retained in the ER, without undergoing Hyp-O-glycosylation. In contrast, the fusion protein becomes fully Hyp-O-glycosylated, and then secreted in SH medium. Transcriptome analysis of the BY-2 cells grown in SH medium vs. MS medium revealed over 16,000 DEGs, with many upregulated DEGs associated with the microtubule-based movement, movement of subcellular component, and microtubule binding. These DEGs are presumably responsible for the enhanced ER-Golgi transport of HypGP-tagged proteins, enabling their glycosylation and secretion in SH medium.

Current status and future prospects in cannabinoid production through in vitro culture and synthetic biology

For centuries, cannabis has been a rich source of fibrous, pharmaceutical, and recreational ingredients. Phytocannabinoids are the most important and well-known class of cannabis-derived secondary metabolites and display a broad range of health-promoting and psychoactive effects. The unique characteristics of phytocannabinoids (e.g., metabolite likeness, multi-target spectrum, and safety profile) have resulted in the development and approval of several cannabis-derived drugs. While most work has focused on the two main cannabinoids produced in the plant, over 150 unique cannabinoids have been identified. To meet the rapidly growing phytocannabinoid demand, particularly many of the minor cannabinoids found in low amounts in planta, biotechnology offers promising alternatives for biosynthesis through in vitro culture and heterologous systems. In recent years, the engineered production of phytocannabinoids has been obtained through synthetic biology both in vitro (cell suspension culture and hairy root culture) and heterologous systems. However, there are still several bottlenecks (e.g., the complexity of the cannabinoid biosynthetic pathway and optimizing the bioprocess), hampering biosynthesis and scaling up the biotechnological process. The current study reviews recent advances related to in vitro culture-mediated cannabinoid production. Additionally, an integrated overview of promising conventional approaches to cannabinoid production is presented. Progress toward cannabinoid production in heterologous systems and possible avenues for avoiding autotoxicity are also reviewed and highlighted. Machine learning is then introduced as a powerful tool to model, and optimize bioprocesses related to cannabinoid production. Finally, regulation and manipulation of the cannabinoid biosynthetic pathway using CRISPR- mediated metabolic engineering is discussed.

Incorporation of Organic Growth Additives to Enhance In Vitro Tissue Culture for Producing Genetically Stable Plants

The growing demand for native planting material in ecological restoration and rehabilitation for agro-silvo-pastoral ecosystems has resulted in a major global industry in their sourcing, multiplication, and sale. Plant tissue culture is used for producing high-quality, disease-free, and true-to-type plants at a fast rate. Micropropagation can help to meet the increasing demand for planting material and afforestation programs. However, in vitro plant propagation is an expensive technique compared to conventional methods using suckers, seeds, and cuttings. Therefore, adopting measures to lower production costs without compromising plant quality is essential. This can be achieved by improving the culture media composition. Incorporating organic growth additives can stimulate tissue growth and increase the number of shoots, leaves, and roots in culture media. Organic growth supplementation speeds up the formation and development of cultures and yields vigorous plants. Plant regeneration from meristems (shoot tips and axillary buds) is a reliable way to produce true-to-type plants compared with callus and somatic embryogenesis regeneration, but in vitro culture environments can be mutagenic. Therefore, detecting somaclonal variations at an early stage of development is considered crucial in propagating plants. The genetic stability of in vitro regenerated plants needs to be ascertained by using DNA-based molecular markers. This review aims to provide up-to-date research progress on incorporating organic growth additives to enhance in vitro tissue culture protocols and to emphasize the importance of using PCR-based molecular markers such as RAPD, ISSR, SSR, and SCoT. The review was assessed based on the peer-reviewed works published in scientific databases including Science Direct, Scopus, Springer, JSTOR, onlinelibrary, and Google Scholar.

Improving yield of a recombinant biologic in a Brassica hairy root manufacturing process

Hairy root systems have proven to be a viable alternative for recombinant protein production. For recalcitrant proteins, maximizing the productivity of hairy root cultures is essential. The aim of this study was to optimize a Brassica rapa rapa hairy root process for secretion of alpha‐ l‐iduronidase (IDUA), a biologic of medical value. The process was first optimized with hairy roots expressing eGFP. For the biomass optimization, the highest biomass yields were achieved in modified Gamborg B5 culture medium. For the secretion induction, the optimized secretion media was obtained with additives (1.5 g/l PVP + 1 mg/l 2,4‐ d + 20.5 g/l KNO₃) resulting in 3.4 fold eGFP secretion when compared to the non‐induced control. These optimized conditions were applied to the IDUA‐expressing hairy root clone, confirming that the highest yields of secreted IDUA occurred when using the defined additive combination. The functionality of the IDUA protein, secreted and intracellular, was confirmed with an enzymatic activity assay. A > 150‐fold increase of the IDUA activity was observed using an optimized secretion medium, compared with a non‐induced medium. We have proven that our B. rapa rapa hairy root system can be harnessed to secrete recalcitrant proteins, illustrating the high potential of hairy roots in plant molecular farming.

Life cycle assessment of plant cell cultures

A novel food such as plant cell culture (PCC) is an important complementary asset for traditional agriculture to tackle global food insecurity. To evaluate environmental impacts of PCC, a life cycle assessment was applied to tobacco bright yellow-2 and cloudberry PCCs. Global warming potential (GWP), freshwater eutrophication potential (FEUP), marine eutrophication potential, terrestrial acidification potential (TAP), stratospheric ozone depletion, water consumption and land use were assessed. The results showed particularly high contributions (82-93%) of electricity consumption to GWP, FEUP and TAP. Sensitivity analysis indicated that using wind energy instead of the average Finnish electricity mix reduced the environmental impacts by 34-81%. Enhancement in the energy efficiency of bioreactor mixing processes and reduction in cultivation time also effectively improved the environmental performance (4-47% reduction of impacts). In comparison with other novel foods, the environmental impacts of the PCC products studied were mostly comparable to those of microalgae products but higher than those of microbial protein products produced by autotrophic hydrogen-oxidizing bacteria. Assayed fresh PCC products were similar or close to GWP of conventionally grown food products and, with technological advancements, can be highly competitive.

Genetic Manipulation and Bioreactor Culture of Plants as a Tool for Industry and Its Applications

In recent years, there has been a considerable increase in interest in the use of transgenic plants as sources of valuable secondary metabolites or recombinant proteins. This has been facilitated by the advent of genetic engineering technology with the possibility for direct modification of the expression of genes related to the biosynthesis of biologically active compounds. A wide range of research projects have yielded a number of efficient plant systems that produce specific secondary metabolites or recombinant proteins. Furthermore, the use of bioreactors allows production to be increased to industrial scales, which can quickly and cheaply deliver large amounts of material in a short time. The resulting plant production systems can function as small factories, and many of them that are targeted at a specific operation have been patented. This review paper summarizes the key research in the last ten years regarding the use of transgenic plants as small, green biofactories for the bioreactor-based production of secondary metabolites and recombinant proteins; it simultaneously examines the production of metabolites and recombinant proteins on an industrial scale and presents the current state of available patents in the field.

Plant Secondary Metabolite Transporters: Diversity, Functionality, and Their Modulation

Secondary metabolites (SMs) play crucial roles in the vital functioning of plants such as growth, development, defense, and survival via their transportation and accumulation at the required site. However, unlike primary metabolites, the transport mechanisms of SMs are not yet well explored. There exists a huge gap between the abundant presence of SM transporters, their identification, and functional characterization. A better understanding of plant SM transporters will surely be a step forward to fulfill the steeply increasing demand for bioactive compounds for the formulation of herbal medicines. Thus, the engineering of transporters by modulating their expression is emerging as the most viable option to achieve the long-term goal of systemic metabolic engineering for enhanced metabolite production at minimum cost. In this review article, we are updating the understanding of recent advancements in the field of plant SM transporters, particularly those discovered in the past two decades. Herein, we provide notable insights about various types of fully or partially characterized transporters from the ABC, MATE, PUP, and NPF families including their diverse functionalities, structural information, potential approaches for their identification and characterization, several regulatory parameters, and their modulation. A novel perspective to the concept of "Transporter Engineering" has also been unveiled by highlighting its potential applications particularly in plant stress (biotic and abiotic) tolerance, SM accumulation, and removal of anti-nutritional compounds, which will be of great value for the crop improvement program. The present study creates a roadmap for easy identification and a better understanding of various transporters, which can be utilized as suitable targets for transporter engineering in future research.

Soluble Expression and Efficient Purification of Recombinant Class I Hydrophobin DewA

Hydrophobins are small proteins (<20 kDa) with an amphipathic tertiary structure that are secreted by various filamentous fungi. Their amphipathic properties provide surfactant-like activity, leading to the formation of robust amphipathic layers at hydrophilic–hydrophobic interfaces, which make them useful for a wide variety of industrial fields spanning protein immobilization to surface functionalization. However, the industrial use of recombinant hydrophobins has been hampered due to low yield from inclusion bodies owing to the complicated process, including an auxiliary refolding step. Herein, we report the soluble expression of a recombinant class I hydrophobin DewA originating from Aspergillus nidulans, and its efficient purification from recombinant Escherichia coli. Soluble expression of the recombinant hydrophobin DewA was achieved by a tagging strategy using a systematically designed expression tag (ramp tag) that was fused to the N-terminus of DewA lacking the innate signal sequence. Highly expressed recombinant hydrophobin DewA in a soluble form was efficiently purified by a modified aqueous two-phase separation technique using isopropyl alcohol. Our approach for expression and purification of the recombinant hydrophobin DewA in E. coli shed light on the industrial production of hydrophobins from prokaryotic hosts.

Cellular engineering of plant cells for improved therapeutic protein production

In vitro cultured plant cells, in particular the tobacco BY-2 cell, have demonstrated their potential to provide a promising bioproduction platform for therapeutic proteins by integrating the merits of whole-plant cultivation systems with those of microbial and mammalian cell cultures. Over the past three decades, substantial progress has been made in improving the plant cell culture system, resulting in a few commercial success cases, such as taliglucerase alfa (Elelyso®), the first FDA-approved recombinant pharmaceutical protein derived from plant cells. However, compared to the major expression hosts (bacteria, yeast, and mammalian cells), plant cells are still largely underutilized, mainly due to low productivity and non-human glycosylation. Modern molecular biology tools, in particular RNAi and the latest genome editing technology CRISPR/Cas9, have been used to modulate the genome of plant cells to create new cell lines that exhibit desired "traits" for producing therapeutic proteins. This review highlights the recent advances in cellular engineering of plant cells towards improved recombinant protein production, including creating cell lines with deficient protease levels or humanized glycosylation, and considers potential development in the future.

Investigating trace metal precipitation in highly concentrated cell culture media with Pourbaix diagrams

Commercial production of therapeutic proteins using mammalian cells requires complex process solutions, and consistency of these process solutions is critical to maintaining product titer and quality between batches. Inconsistencies between process solutions prepared at bench and commercial scale may be due to differences in mixing time, temperature, and pH which can lead to precipitation and subsequent removal via filtration of critical solution components such as trace metals. Pourbaix diagrams provide a useful tool to model the solubility of trace metals and were applied to troubleshoot the scale-up of nutrient feed preparation after inconsistencies in product titer were observed between bench- and manufacturing-scale batches. Pourbaix diagrams modeled the solubility of key metals in solution at various stages of the nutrient feed preparation and identified copper precipitation as the likely root cause of inconsistent medium stability at commercial scale. Copper precipitation increased proportionally with temperature in bench-scale preparations of nutrient feed and temperature was identified as the root cause of copper precipitation at the commercial scale. Additionally, cell culture copper titration studies performed in bench-scale bioreactors linked copper-deficient mammalian cell culture to inconsistent titers at the commercial scale. Pourbaix diagrams can predict when trace metals are at risk of precipitating and can be used to mitigate risk during the scale-up of complex medium preparations.

Cryopreservation of plant cell cultures - Diverse practices and protocols

Plant cell cultures can be used as biotechnological platforms for the commercial production of small-molecule active ingredients and recombinant proteins, such as biopharmaceuticals. This requires the cryopreservation of well-characterized cell lines as master cell banks from which uniform working cell banks can be derived to ensure high batch-to-batch reproducibility during production campaigns. However, the cryopreservation of plant cells is challenging due to their low viability and poor regrowth after thawing. Three approaches have been developed: slow freezing, vitrification, and encapsulation-dehydration. Typically, the protocols are iteratively adapted to accommodate the properties of different plant cell lines, taking time and resources while achieving moderate success. Since standardized processes are a prerequisite for industrial applications, this review presents an in-depth analysis of the different procedures for cryopreservation of plant suspension cell cultures, highlighting relevant parameters for effective cryopreservation and the re-establishment of vigorous plant cell cultures within weeks. The protocol variants are grouped into modules that facilitate the directed improvement of each step and allow protocol evolution by module recombination. Ultimately, such improved cryopreservation protocols will form the basis of processes that comply with good manufacturing practice and attract major biopharmaceutical companies to the benefits of plant molecular farming.

Plant cell cultures as food-aspects of sustainability and safety

Sustainability and safety aspects of plant cell cultures as food are presented. Applicability of dairy side streams as carbon source and use of natural growth enhancers in cultivation are shown. Biotechnologically produced cellular products are currently emerging to replace and add into the portfolio of agriculturally derived commodities. Plant cell cultures used for food could supplement current food production. However, still many aspects need to be resolved before this new food concept can enter the market. Issues related to sustainability and safety for human consumption are relevant for both consumers and regulators. In this study, two plant cell cultures, deriving from arctic bramble (Rubus arcticus) and birch (Betula pendula), were cultivated using lactose-rich dairy side streams as alternative carbon sources to replace sucrose. Biomasses were comparable to those of original plant cell culture media when up to 83% and 75% of the original sucrose was replaced by these side streams for arctic bramble and birch cell cultures, respectively. Furthermore, nutritional composition or sensory properties were not compromised. Synthetic plant growth regulators were replaced by natural components, such as coconut water and IAA for several subculture cycles. Finally, it was shown that only trace amounts of free growth regulators are present in the cells at the harvesting point and assessment by freshwater crustaceans assay indicated that toxicity of the cells was not exceeding that of traditionally consumed bilberry fruit.

Transient protein expression in tobacco BY-2 plant cell packs using single and multi-cassette replicating vectors

KEY MESSAGE

This is the first evidence that replicating vectors can be successfully used for transient protein expression in BY-2 plant cell packs. Transient recombinant protein expression in plants and recently also plant cell cultures are of increasing interest due to the speed, safety and scalability of the process. Currently, studies are focussing on the design of plant virus-derived vectors to achieve higher amounts of transiently expressed proteins in these systems. Here we designed and tested replicating single and multi-cassette vectors that combine elements for enhanced replication and hypertranslation, and assessed their ability to express and particularly co-express proteins by Agrobacterium-mediated transient expression in tobacco BY-2 plant cell packs. Substantial yields of green and red fluorescent proteins of up to ~ 700 ng/g fresh mass were detected in the plant cells along with position-dependent expression. This is the first evidence of the ability of replicating vectors to transiently express proteins in BY-2 plant cell packs.

Technoeconomic analysis of semicontinuous bioreactor production of biopharmaceuticals in transgenic rice cell suspension cultures

Biopharmaceutical protein production using transgenic plant cell bioreactor processes offers advantages over microbial and mammalian cell culture platforms in its ability to produce complex biologics with simple chemically defined media and reduced biosafety concerns. A disadvantage of plant cells from a traditional batch bioprocessing perspective is their slow growth rate which has motivated us to develop semicontinuous and/or perfusion processes. Although the economic benefits of plant cell culture bioprocesses are often mentioned in the literature, to our knowledge no rigorous technoeconomic models or analyses have been published. Here we present technoeconomic models in SuperPro Designer® for the large-scale production of recombinant butyrylcholinesterase (BChE), a prophylactic/therapeutic bioscavenger against organophosphate nerve agent poisoning, in inducible transgenic rice cell suspension cultures. The base facility designed to produce 25 kg BChE per year utilizing two-stage semicontinuous bioreactor operation manufactures a single 400 mg dose of BChE for $263. Semicontinuous operation scenarios result in 4-11% reduction over traditional two-stage batch operation scenarios. In addition to providing a simulation tool that will be useful to the plant-made pharmaceutical community, the model also provides a computational framework that can be used for other semicontinuous or batch bioreactor-based processes.

Engineering 'designer' glycomodules for boosting recombinant protein secretion in tobacco hairy root culture and studying hydroxyproline-O-glycosylation process in plants

The key technical bottleneck for exploiting plant hairy root cultures as a robust bioproduction platform for therapeutic proteins has been low protein productivity, particularly low secreted protein yields. To address this, we engineered novel hydroxyproline (Hyp)-O-glycosylated peptides (HypGPs) into tobacco hairy roots to boost the extracellular secretion of fused proteins and to elucidate Hyp-O-glycosylation process of plant cell wall Hyp-rich glycoproteins. HypGPs representing two major types of cell wall glycoproteins were examined: an extensin module consisting of 18 tandem repeats of 'Ser-Hyp-Hyp-Hyp-Hyp' motif or (SP4)18 and an arabinogalactan protein module consisting of 32 tandem repeats of 'Ser-Hyp' motif or (SP)32 . Each module was expressed in tobacco hairy roots as a fusion to the enhanced green fluorescence protein (EGFP). Hairy root cultures engineered with a HypGP module secreted up to 56-fold greater levels of EGFP, compared with an EGFP control lacking any HypGP module, supporting the function of HypGP modules as a molecular carrier in promoting efficient transport of fused proteins into the culture media. The engineered (SP4)18 and (SP)32 modules underwent Hyp-O-glycosylation with arabino-oligosaccharides and arabinogalactan polysaccharides, respectively, which were essential in facilitating secretion of the fused EGFP protein. Distinct non-Hyp-O-glycosylated (SP4)18 -EGFP and (SP)32 -EGFP intermediates were consistently accumulated within the root tissues, indicating a rate-limiting trafficking and/or glycosylation of the engineered HypGP modules. An updated model depicting the intracellular trafficking, Hyp-O-glycosylation and extracellular secretion of extensin-styled (SP4)18 module and AGP-styled (SP)32 module is proposed.

Transient expression of etanercept therapeutic protein in tobacco (Nicotiana tabacum L.)

Etanercept is a recombinant fusion protein of TNFR2 with the Fc portion of human IgG1. Etanercept, an anti-TNF drug, treats autoimmune diseases and improves patients' health. The main goal of the present study was to investigate the possibility of expressing recombinant protein of etanercept in a plant system. For this aim, first a modified version of pCAMBIA1305.1 plasmid with a new multiple cloning site and signal sequence of KDEL for protein secretion was constructed (pCAMBIA1305.1-linker). Then etanercept gene was cloned into the linker fragment of pCAMBIA1305.1-linker vector. Cloning was confirmed by PCR, enzymatic digestion and sequencing techniques. To evaluate the transient expression of the gene, agroinfiltrated tobacco leaves were inoculated with Agrobacterium tumefaciens containing etanercept gene cassette. The recombinant etanercept protein was examined by dot blot and ELISA assays. Our results using anti-human IgG HRP-conjugated antibody confirmed a high level expression of etanercept gene in the tobacco leaves.

Hydrophobins: multifunctional biosurfactants for interface engineering

Hydrophobins are highly surface-active proteins that have versatile potential as agents for interface engineering. Due to the large and growing number of unique hydrophobin sequences identified, there is growing potential to engineer variants for particular applications using protein engineering and other approaches. Recent applications and advancements in hydrophobin technologies and production strategies are reviewed. The application space of hydrophobins is large and growing, including hydrophobic drug solubilization and delivery, protein purification tags, tools for protein and cell immobilization, antimicrobial coatings, biosensors, biomineralization templates and emulsifying agents. While there is significant promise for their use in a wide range of applications, developing new production strategies is a key need to improve on low recombinant yields to enable their use in broader applications; further optimization of expression systems and yields remains a challenge in order to use designed hydrophobin in commercial applications.