Engineering Considerations to Produce Bioactive Compounds from Plant Cell Suspension Culture in Bioreactors

Bioreactor Systems for Plant Cell Cultivation at the Institute of Plant Physiology of the Russian Academy of Sciences: 50 Years of Technology Evolution from Laboratory to Industrial Implications

The cultivation of plant cells in large-scale bioreactor systems has long been considered a promising alternative for the overexploitation of wild plants as a source of bioactive phytochemicals. This idea, however, faced multiple constraints upon realization, resulting in very few examples of technologically feasible and economically effective biotechnological companies. The bioreactor cultivation of plant cells is challenging. Even well-growing and highly biosynthetically potent cell lines require a thorough optimization of cultivation parameters when upscaling the cultivation process from laboratory to industrial volumes. The optimization includes, but is not limited to, the bioreactor's shape and design, cultivation regime (batch, fed-batch, continuous, semi-continuous), aeration, homogenization, anti-foaming measures, etc., while maintaining a high biomass and metabolite production. Based on the literature data and our experience, the cell cultures often demonstrate cell line- or species-specific responses to parameter changes, with the dissolved oxygen concentration (pO2) and shear stress caused by stirring being frequent growth-limiting factors. The mass transfer coefficient also plays a vital role in upscaling the cultivation process from smaller to larger volumes. The Experimental Biotechnological Facility at the K.A. Timiryazev Institute of Plant Physiology has operated since the 1970s and currently hosts a cascade of bioreactors from the laboratory (20 L) to the pilot (75 L) and a semi-industrial volume (630 L) adapted for the cultivation of plant cells. In this review, we discuss the most appealing cases of the cell cultivation process's adaptation to bioreactor conditions featuring the cell cultures of medicinal plants Dioscorea deltoidea Wall. ex Griseb., Taxus wallichiana Zucc., Stephania glabra (Roxb.) Miers, Panax japonicus (T. Nees) C.A.Mey., Polyscias filicifolia (C. Moore ex E. Fourn.) L.H. Bailey, and P. fruticosa L. Harms. The results of cell cultivation in bioreactors of different types and designs using various cultivation regimes are covered and compared with the literature data. We also discuss the role of the critical factors affecting cell behavior in bioreactors with large volumes.

The advent of plant cells in bioreactors

Ever since agriculture started, plants have been bred to obtain better yields, better fruits, or sustainable products under uncertain biotic and abiotic conditions. However, a new way to obtain products from plant cells emerged with the development of recombinant DNA technologies. This led to the possibility of producing exogenous molecules in plants. Furthermore, plant chemodiversity has been the main source of pharmacological molecules, opening a field of plant biotechnology directed to produce high quality plant metabolites. The need for different products by the pharma, cosmetics agriculture and food industry has pushed again to develop new procedures. These include cell production in bioreactors. While plant tissue and cell culture are an established technology, beginning over a hundred years ago, plant cell cultures have shown little impact in biotechnology projects, compared to bacterial, yeasts or animal cells. In this review we address the different types of bioreactors that are currently used for plant cell production and their usage for quality biomolecule production. We make an overview of Nicotiana tabacum, Nicotiana benthamiana, Oryza sativa, Daucus carota, Vitis vinifera and Physcomitrium patens as well-established models for plant cell culture, and some species used to obtain important metabolites, with an insight into the type of bioreactor and production protocols.

Suspension Cell Culture of Polyscias fruticosa (L.) Harms in Bubble-Type Bioreactors-Growth Characteristics, Triterpene Glycosides Accumulation and Biological Activity

Polyscias fruticosa (L.) Harms, or Ming aralia, is a medicinal plant of the Araliaceae family, which is highly valued for its antitoxic, anti-inflammatory, analgesic, antibacterial, anti-asthmatic, adaptogenic, and other properties. The plant can be potentially used to treat diabetes and its complications, ischemic brain damage, and Parkinson's disease. Triterpene glycosides of the oleanane type, such as 3-O-[β-D-glucopyranosyl-(1→4)-β-D-glucuronopyranosyl] oleanolic acid 28-O-β-D-glucopyranosyl ester (PFS), ladyginoside A, and polysciosides A-H, are mainly responsible for biological activities of this species. In this study, cultivation of the cell suspension of P. fruticosa in 20 L bubble-type bioreactors was attempted as a sustainable method for cell biomass production of this valuable species and an alternative to overexploitation of wild plant resources. Cell suspension cultivated in bioreactors under a semi-continuous regime demonstrated satisfactory growth with a specific growth rate of 0.11 day-1, productivity of 0.32 g (L · day)-1, and an economic coefficient of 0.16 but slightly lower maximum biomass accumulation (~6.8 g L-1) compared to flask culture (~8.2 g L-1). Triterpene glycosides PFS (0.91 mg gDW-1) and ladyginoside A (0.77 mg gDW-1) were detected in bioreactor-produced cell biomass in higher concentrations compared to cells grown in flasks (0.50 and 0.22 mg gDW-1, respectively). In antibacterial tests, the minimum inhibitory concentrations (MICs) of cell biomass extracts against the most common pathogens Staphylococcus aureus, methicillin-resistant strain MRSA, Pseudomonas aeruginosa, and Escherichia coli varied within 250-2000 µg mL-1 which was higher compared to extracts of greenhouse plant leaves (MIC = 4000 µg mL-1). Cell biomass extracts also exhibited antioxidant activity, as confirmed by DPPH and TEAC assays. Our results suggest that bioreactor cultivation of P. fruticosa suspension cell culture may be a perspective method for the sustainable biomass production of this species.

Biosynthesis of Functional Silver Nanoparticles Using Callus and Hairy Root Cultures of Aristolochia manshuriensis

This study delves into the novel utilization of Aristolochia manshuriensis cultured cells for extracellular silver nanoparticles (AgNPs) synthesis without the need for additional substances. The presence of elemental silver has been verified using energy-dispersive X-ray spectroscopy, while distinct surface plasmon resonance peaks were revealed by UV-Vis spectra. Transmission and scanning electron microscopy indicated that the AgNPs, ranging in size from 10 to 40 nm, exhibited a spherical morphology. Fourier-transform infrared analysis validated the abilty of A. manshuriensis extract components to serve as both reducing and capping agents for metal ions. In the context of cytotoxicity on embryonic fibroblast (NIH 3T3) and mouse neuroblastoma (N2A) cells, AgNPs demonstrated varying effects. Specifically, nanoparticles derived from callus cultures exhibited an IC50 of 2.8 µg/mL, effectively inhibiting N2A growth, whereas AgNPs sourced from hairy roots only achieved this only at concentrations of 50 µg/mL and above. Notably, all studied AgNPs' treatment-induced cytotoxicity in fibroblast cells, yielding IC50 values ranging from 7.2 to 36.3 µg/mL. Furthermore, the findings unveiled the efficacy of the synthesized AgNPs against pathogenic microorganisms impacting both plants and animals, including Agrobacterium rhizogenes, A. tumefaciens, Bacillus subtilis, and Escherichia coli. These findings underscore the effectiveness of biotechnological methodologies in offering advanced and enhanced green nanotechnology alternatives for generating nanoparticles with applications in combating cancer and infectious disorders.

Natural products of pentacyclic triterpenoids: from discovery to heterologous biosynthesis

Covering: up to 2022Pentacyclic triterpenoids are important natural bioactive substances that are widely present in plants and fungi. They have significant medicinal efficacy, play an important role in reducing blood glucose and protecting the liver, and have anti-inflammatory, anti-oxidation, anti-fatigue, anti-viral, and anti-cancer activities. Pentacyclic triterpenoids are derived from the isoprenoid biosynthetic pathway, which generates common precursors of triterpenes and steroids, followed by cyclization with oxidosqualene cyclases (OSCs) and decoration via cytochrome P450 monooxygenases (CYP450s) and glycosyltransferases (GTs). Many biosynthetic pathways of triterpenoid saponins have been elucidated by studying their metabolic regulation network through the use of multiomics and identifying their functional genes. Unfortunately, natural resources of pentacyclic triterpenoids are limited due to their low content in plant tissues and the long growth cycle of plants. Based on the understanding of their biosynthetic pathway and transcriptional regulation, plant bioreactors and microbial cell factories are emerging as alternative means for the synthesis of desired triterpenoid saponins. The rapid development of synthetic biology, metabolic engineering, and fermentation technology has broadened channels for the accumulation of pentacyclic triterpenoid saponins. In this review, we summarize the classification, distribution, structural characteristics, and bioactivity of pentacyclic triterpenoids. We further discuss the biosynthetic pathways of pentacyclic triterpenoids and involved transcriptional regulation. Moreover, the recent progress and characteristics of heterologous biosynthesis in plants and microbial cell factories are discussed comparatively. Finally, we propose potential strategies to improve the accumulation of triterpenoid saponins, thereby providing a guide for their future biomanufacturing.

Bioreactor configurations for adventitious root culture: recent advances toward the commercial production of specialized metabolites

In vitro plant cell and organ cultures are appealing alternatives to traditional methods of producing valuable specialized metabolites for use as: pharmaceuticals, food additives, cosmetics, perfumes, and agricultural chemicals. Cell cultures have been adopted for the production of specialized metabolites in certain plants. However, in certain other systems, adventitious roots are superior to cell suspension cultures as they are organized structures that accumulate high levels of specialized metabolites. The cultivation of adventitious roots has been investigated in various bioreactor systems, including: mechanically agitated, pneumatically agitated, and modified bioreactors. The main relevance and importance of this work are to develop a long-lasting industrial biotechnological technology as well as to improve the synthesis of these metabolites from the plant in vitro systems. These challenges are exacerbated by: the peculiarities of plant cell metabolism, the complexity of specialized metabolite pathways, the proper selection of bioreactor systems, and bioprocess optimization. This review's major objective is to analyze several bioreactor types for the development of adventitious roots, as well as the advantages and disadvantages of each type of bioreactor, and to describe the strategies used to increase the synthesis of specialized metabolites. This review also emphasizes current advancements in the field, and successful instances of scaled-up cultures and the generation of specialized metabolites for commercial purposes are also covered.

10th Anniversary of Plants-Recent Advances and Further Perspectives

Published for the first time in 2012, Plants will celebrate its 10th anniversary [...].

Phenolic Compounds from Wild Plant and In Vitro Cultures of Ageratina pichichensis and Evaluation of Their Antioxidant Activity

Ageratina pichichensis, is commonly used in traditional Mexican medicine. In vitro cultures were established from wild plant (WP) seeds, obtaining in vitro plant (IP), callus culture (CC), and cell suspension culture (CSC) with the objective to determine total phenol content (TPC) and flavonoids (TFC), as well as their antioxidant activity by DPPH, ABTS and TBARS assays, added to the compound's identification and quantification by HPLC, from methanol extracts obtained by sonication. CC showed significantly higher TPC and TFC than WP and IP, while CSC produced 2.0-2.7 times more TFC than WP, and IP produced only 14.16% TPC and 38.8% TFC compared with WP. There were identified compounds such as epicatechin (EPI), caffeic acid (CfA), and p-coumaric acid (pCA) in in vitro cultures that were not found in WP. The quantitative analysis shows gallic acid (GA) as the least abundant compound in samples, whereas CSC produced significantly more EPI and CfA than CC. Despite these results, in vitro cultures show lower antioxidant activity than WP, for DPPH and TBARS WP > CSC > CC > IP and ABTS WP > CSC = CC > IP. Overall, A. pichichensis WP and in vitro cultures produce phenolic compounds with antioxidant activity, especially CC and CSC, which are shown to be a biotechnological alternative for obtaining bioactive compounds.

Influence of Different Precursors on Content of Polyphenols in Camellia sinensis In Vitro Callus Culture

Plant tissue cultures are considered as potential producers of biologically active plant metabolites, which include various phenolic compounds that can be used to maintain human health. Moreover, in most cases, their accumulation is lower than in the original explants, which requires the search for factors and influences for the intensification of this process. In this case, it is very promising to use the precursors of their biosynthesis as potential "regulators" of the various metabolites' formation. The purpose of our research was to study the effect of L-phenylalanine (PhA, 3 mM), trans-cinnamic acid (CA, 1 mM) and naringenin (NG, 0.5 mM), as components of various stages of phenolic metabolism, on accumulation of various phenolic compound classes, including phenylpropanoids, flavans and proanthocyanidins, as well as the content of malondialdehyde in in vitro callus culture of the tea plant (Camellia sinensis L.). According to the data obtained, the precursors' influence did not lead to changes in the morphology and water content of the cultures. At the same time, an increase in the total content of phenolic compounds, as well as phenylpropanoids, flavans and proanthocyanidins, was noted in tea callus cultures. Effectiveness of precursor action depends on its characteristics and the exposure duration, and was more pronounced in the treatments with PhA. This compound can be considered as the most effective precursor regulating phenolic metabolism, contributing to a twofold increase in the total content of phenolic compounds, flavanes and proanthocyanidins, and a fourfold increase in phenylpropanoids in tea callus cultures.

Genetic Containment for Molecular Farming

Plant molecular farming can provide humans with a wide variety of plant-based products including vaccines, therapeutics, polymers, industrial enzymes, and more. Some of these products, such as Taxol, are produced by endogenous plant genes, while many others require addition of genes by artificial gene transfer. Thus, some molecular farming plants are transgenic (or cisgenic), while others are not. Both the transgenic nature of many molecular farming plants and the fact that the products generated are of high-value and specific in purpose mean it is essential to prevent accidental cross-over of molecular farming plants and products into food or feed. Such mingling could occur either by gene flow during plant growth and harvest or by human errors in material handling. One simple approach to mitigate possible transfer would be to use only non-food non-feed species for molecular farming purposes. However, given the extent of molecular farming products in development, testing, or approval that do utilize food or feed crops, a ban on use of these species would be challenging to implement. Therefore, other approaches will need to be considered for mitigation of cross-flow between molecular farming and non-molecular-farming plants. This review summarized some of the production systems available for molecular farming purposes and options to implement or improve plant containment.

Effect of Different Cytokinins on Shoot Outgrowth and Bioactive Compounds Profile of Lemograss Essential Oil

Lemongrass (Cymbopogon citratus) essential oil (EO) is a major source of bioactive compounds (BC) with anticancer activity such as α-citral, limonene, geraniol, geranyl acetate, and β-caryophyllene. Comparative studies about cytokinin effects on BC profiles in lemongrass are missing. Here, we evaluated four cytokinins (2iP, tZ, BAP, and KIN) in two different osmotic media, MS-N (3% sucrose, 3 g L−1 Gelrite™) and MS-S (5% sucrose, 5 g L−1 Gelrite™). It results in a higher multiplication rate in BAP containing medium compared to tZ, KIN, and 2iP (p ≤ 0.05). While shoots grown on MS-N/BAP, tZ, and KIN exhibited a highly branching morphology, MS-N/2iP produced a less branching architecture. BC profile analysis of established plants in pots revealed that their maxima production depends on the in vitro shoot growth conditions: i.e., highest content (80%) of α-citral in plants that were cultured in MS-S/BAP (p ≤ 0.05), limonene (41%) in MS-N/2iP, or geranyl acetate (25.79%) in MS-S/2iP. These results indicate that it is possible to increase or address the production of BC in lemongrass by manipulating the cytokinin type and osmotic pressure in culture media. The culture protocol described here is currently successfully applied for somatic embryogenesis induction and genetic transformation in lemongrass.

Establishment of Stem Cell-like Cells of Sida hermaphrodita (L.) Rusby from Explants Containing Cambial Meristems

The in vitro cultures of plant stem cells and stem cell-like cells can be established from tissues containing meristematic cells. Chemical compounds—as well as their production potential—is among the emerging topics of plant biotechnology. We induced the callus cell biomass growth and characterized the parameters indicating the presence of stem cells or stem cell-like cells. Four types of explants (stem, petiole, leaf, root) from Sida hermaphrodita (L.) Rusby and various combinations of auxins and cytokinins were tested for initiation of callus, growth of sub-cultivated callus biomass, and establishment of stem cells or stem cell-like cells. Induction of callus and its growth parameters were significantly affected both by the explant type and the combination of used plant growth hormones and regulators. The responsibility for callus initiation and growth was the highest in stem-derived explants containing cambial meristematic cells. Growth parameters of callus biomass and specific characteristics of vacuoles confirmed the presence of stem cells or stem cell-like cells in sub-cultivated callus cell biomass. Establishment of in vitro stem cell or stem cell-like cell cultures in S. hermaphrodita can lead to the development of various applications of in vitro cultivation systems as well as alternative applications of this crop.

Plant cell cultures: An enzymatic tool for polyphenolic and flavonoid transformations

BACKGROUND

In the pharmaceutical sector, tissue culture techniques for large-scale production of natural chemicals can be a less expensive alternative to large-scale synthesis. Although recent biotransformation research have used plant cell cultures to target a wide range of bioactive compounds, more compiled information and synopses are needed to better understand metabolic pathways and improve biotransformation efficiencies.

PURPOSE

This report reviews the biochemical transformation of phenolic natural products by plant cell cultures in order to identify potential novel biotechnological approaches for ensuring more homogeneous and stable phenolic production year-round under controlled environmental conditions.

METHODS

Articles on the use of plant cell culture for polyphenolic and flavonoid transformations (1988 - 2021) were retrieved from SciFinder, PubMed, Scopus, and Web of Science through electronic and manual search in English. Following that, the authors chose the required papers based on the criteria they defined. The following keywords were used for the online search: biotransformation, Plant cell cultures, flavonoids, phenolics, and pharmaceutical products.

RESULTS

The initial search found a total of 96 articles. However, only 70 of them were selected as they met the inclusion criteria defined by the authors. The analysis of these studies revealed that plant tissue culture is applicable for the large-scale production of plant secondary metabolites including the phenolics, which have high therapeutic value.

CONCLUSION

Plant tissue cultures could be employed as an efficient technique for producing secondary metabolites including phenolics. Phenolics possess a wide range of therapeutic benefits, as anti-oxidant, anti-cancer, and anti-inflammatory properties. Callus culture, suspension cultures, transformation, and other procedures have been used to improve the synthesis of phenolics. Their production on a large scale is now achievable. More breakthroughs will lead to newer insights and, without a doubt, to a new era of phenolics-based pharmacological agents for the treatment of a variety of infectious and degenerative disorders.