Large-scale cultivation of Catharanthus roseus cells: production of ajmalicine in a 20-l airlift bioreactor

Obtaining 2,3-Dihydrobenzofuran and 3-Epilupeol from Ageratina pichinchensis (Kunth) R.King & Ho.Rob. Cell Cultures Grown in Shake Flasks under Photoperiod and Darkness, and Its Scale-Up to an Airlift Bioreactor for Enhanced Production

Ageratina pichinchensis (Kunth) R.King & Ho.Rob. is a plant used in traditional Mexican medicine, and some biotechnological studies have shown that its calluses and cell suspension cultures can produce important anti-inflammatory compounds. In this study, we established a cell culture of A. pichinchensis in a 2 L airlift bioreactor and evaluated the production of the anti-inflammatory compounds 2,3-dihydrobenzofuran (1) and 3-epilupeol (2). The maximum biomass production (11.90 ± 2.48 g/L) was reached at 11 days of culture and cell viability was between 80% and 90%. Among kinetic parameters, the specific growth rate (µ) was 0.2216 days^-1 and doubling time (td) was 3.13 days. Gas chromatography coupled with mass spectrometry (GC-MS) analysis of extracts showed the maximum production of compound 1 (903.02 ± 41.06 µg/g extract) and compound 2 (561.63 ± 10.63 µg/g extract) at 7 and 14 days, respectively. This study stands out for the significant production of 2,3-dihydrobenzofuran and 3-epilupeol and by the significant reduction in production time compared to callus and cell suspension cultures, previously reported. To date, these compounds have not been found in the wild plant, i.e., its production has only been reported in cell cultures of A. pichinchensis. Therefore, plant cell cultured in an airlift reactor can be an alternative for the improved production of these anti-inflammatory compounds.

Medicinal Plants: Guests and Hosts in the Heterologous Expression of High-Value Products

Medicinal plants play an important dual role in the context of the heterologous expression of high-value pharmaceutical products. On the one hand, the classical biochemical and modern omics approaches allowed for the discovery of various genes encoding biosynthetic pathways in medicinal plants. Recombinant DNA technology enabled introducing these genes and regulatory elements into host organisms and enhancing the heterologous production of the corresponding secondary metabolites. On the other hand, the transient expression of foreign DNA in plants facilitated the production of numerous proteins of pharmaceutical importance. This review summarizes several success stories of the engineering of plant metabolic pathways in heterologous hosts. Likewise, a few examples of recombinant protein expression in plants for therapeutic purposes are also highlighted. Therefore, the importance of medicinal plants has grown immensely as sources for valuable products of low and high molecular weight. The next step ahead for bioengineering is to achieve more success stories of industrial-scale production of secondary plant metabolites in microbial systems and to fully exploit plant cell factories' commercial potential for recombinant proteins.

Comparative study of withanolide production and the related transcriptional responses of biosynthetic genes in fungi elicited cell suspension culture of Withania somnifera in shake flask and bioreactor

Ashwagandha (Withania somnifera) is one of the most reputed medicinal plants in the traditional medicinal system. In this study, cell suspension culture of W. somnifera was elicited with cell homogenates of fungi (A. alternata, F. solani, V. dahliae and P. indica) in shake flask and the major withanolides like withanolide A, withaferin A and withanone were analysed. Simultaneously expression levels of key pathway genes from withanolides biosynthetic pathways were also checked via quantitative PCR in shake flask as well as in bioreactor. The results show that highest gene expression of 10.8, 5.8, 4.9, and 3.3 folds were observed with HMGR among all the expressed genes in cell suspension cultures with cell homogenates of 3% P. indica, 5% V. dahliae, 3% A. alternata and 3% F. solani, respectively, in comparison to the control in shake flask. Optimized concentration of cell homogenate of P. indica (3% v/v) was added to the growing culture in 5.0-l bioreactor under optimized up-scaling conditions and harvested after 22 days. The genes of MVA, MEP and withanolides biosynthetic pathways like HMGR, SS, SE, CAS, FPPS, DXR and DXS were up-regulated by 12.5, 4.9, 2.18, 4.65, 2.34, 1.89 and 1.4 folds, respectively in bioreactor. The enhancement of biomass (1.13 fold) and withanolides [withanolide A (1.7), withaferin A (1.5), and withanone (1.5) folds] in bioreactor in comparison to shake flask was also found to be in line with the up-regulation of genes of withanolide biosynthetic pathways.

Engineering overexpression of ORCA3 and strictosidine glucosidase in Catharanthus roseus hairy roots increases alkaloid production

Catharanthus roseus produces many pharmaceutically important terpenoid indole alkaloids (TIAs) such as vinblastine, vincristine, ajmalicine, and serpentine. Past metabolic engineering efforts have pointed to the tight regulation of the TIA pathway and to multiple rate-limiting reactions. Transcriptional regulator ORCA3 (octadecanoid responsive Catharanthus AP2-domain protein), activated by jasmonic acid, plays a central role in regulating the TIA pathway. In this study, overexpressing ORCA3 under the control of a glucocorticoid-inducible promoter in C. roseus hairy roots resulted in no change in the total amount of TIAs measured. RT-qPCR results showed that ORCA3 overexpression triggered the upregulation of transcripts of most of the known TIA pathway genes. One notable exception was the decrease in strictosidine glucosidase (SGD) transcripts. These results corresponded to previously published results. In this study, ORCA3 and SGD were both engineered in hairy roots under the control of a glucocorticoid-inducible promoter. Co-overexpression of ORCA3 and SGD resulted in a significant (p < 0.05) increase in serpentine by 44 %, ajmalicine by 32 %, catharanthine by 38 %, tabersonine by 40 %, lochnericine by 60 % and hörhammericine by 56 % . The total alkaloid pool was increased significantly by 47 %. Thus, combining overexpression of a positive regulator and a pathway gene which is not controlled by this regulator provided a way to enhance alkaloid production.

Improved sanguinarine production via biotic and abiotic elicitations and precursor feeding in cell suspensions of latex-less variety of Papaver somniferum with their gene expression studies and upscaling in bioreactor

Elicitors play an important role in challenging the plant defense system through plant-environment interaction and thus altering the secondary metabolite production. Culture filtrates of four endophytic fungi, namely, Chaetomium globosum, Aspergillus niveoglaucus, Paecilomyces lilacinus, and Trichoderma harzianum were tested on embryogenic cell suspensions of latex-less Papaver somniferum in dose-dependent kinetics. Besides this, abiotic elicitors salicylic acid, hydrogen peroxide, and carbon dioxide were also applied for improved sanguinarine production. Maximum biomass accumulation (growth index (GI) = 293.50 ± 14.82) and sanguinarine production (0.090 ± 0.008 % dry wt.) were registered by addition of 3.3 % v/v T. harzanium culture filtrate. Interestingly, it was further enhanced (GI = 323.40 ± 25.30; 0.105 ± 0.008 % dry wt.) when T. harzanium culture filtrate was employed along with 50 μM shikimate. This was also supported by real-time (RT) (qPCR), where 8-9-fold increase in cheilanthifoline synthase (CFS), stylopine synthase (STS), tetrahydroprotoberberine cis-N-methyltransferase (TNMT), and protopine 6-hydroxylase (P6H) transcripts was observed. Among abiotic elicitors, while hydrogen peroxide and carbon dioxide registered low level of sanguinarine accumulation, maximum sanguinarine content was detected by 250 μM salicylic acid (0.058 ± 0.003 % dry wt.; GI = 172.75 ± 13.40). RT (qPCR) also confirms the downregulation of sanguinarine pathway on CO2 supplementation. Various parameters ranging from agitation speed (70 rpm), impeller type (marine), media volume (2 l), inoculum weight (100 g), and culture duration (9 days) were optimized during upscaling in 5-l stirred tank bioreactor to obtain maximum sanguinarine production (GI = 434.00; 0.119 ± 0.070 % dry wt.). Addition of 3.3 % v/v T. harzanium culture filtrate and 50-μM shikimate was done on the 6th day of bioreactor run.

Tryptophan over-producing cell suspensions of Catharanthus roseus (L) G. Don and their up-scaling in stirred tank bioreactor: detection of a phenolic compound with antioxidant potential

Five cell suspension lines of Catharanthus roseus resistant to 5-methyl tryptophan (5-MT; an analogue of tryptophan) were selected and characterized for growth, free tryptophan content and terpenoid indole alkaloid accumulation. These lines showed differential tolerance to analogue-induced growth inhibition by 30 to 70 mg/l 5-MT supplementation (LD(50) = 7-15 mg/l). Lines P40, D40, N30, D50 and P70 recorded growth indices (i.e. percent increment over the initial inoculum weight) of 840.9, 765.0, 643.9, 585.7 and 356.5 in the absence and, 656.7, 573.9, 705.8, 489.0 and 236.0 in the presence of 5-MT after 40 days of culture, respectively. A corresponding increment in the free tryptophan level ranging from 46.7 to 160.0 μg/g dry weight in the absence and 168.0 to 468.0 μg/g dry weight in the presence was noted in the variant lines. Higher tryptophan accumulation of 368.0 and 468.0 g/g dry weight in lines N30 and P40 in 5-MT presence also resulted in higher alkaloid accumulation (0.65 to 0.90 % dry weight) in them. High-performance liquid chromatography (HPLC) analysis of the crude alkaloid extracts of the selected lines did not show the presence of any pharmaceutically important monomeric or dimeric alkaloids except catharanthine in traces in the N30 line that was also unique in terms of a chlorophyllous green phenotype. The N30 line under optimized up-scaling conditions in a 7-l stirred tank bioreactor using Murashige and Skoog medium containing 2 mg/l α-naphthalene acetic acid and 0.2 mg/l kinetin attained 18-folds biomass accumulation within 8 weeks. Interestingly, the cell biomass yield was enhanced to 30-folds if 30 mg/l 5-MT was added in the bioreactor vessel one week prior to harvest. Crude alkaloid extract of the cells grown in shake flask and this bioreactor batch also showed the formation of yellow-coloured crystals which upon (1)HNMR and ESI-MS analysis indicated a phenolic identity. This crude alkaloid extract of bioreactor-harvested cells containing this compound at 50 μg/ml concentration registered 65.21, 17.75, 97.0, 100 % more total antioxidant capacity, reducing power, total phenolic content, and ferric-reducing antioxidant power, respectively, when compared with that of extracts of cells grown in shake flask cultures. The latter, however, showed 57.47 % better radical scavenging activity (DPPH) than the bioreactor-harvested cells.

Studied enhancement strategies for phytoestrogens production in shake flasks by suspension culture of Psoralea corylifolia

This study proposed secondary metabolites incremental yield due to manipulation of nutrient components into the culture medium. To validate this, the effects of nutrients such as carbon, phosphate and nitrogen on growth and production of phytoestrogens daidzein and genistein by suspension cultures of Psoralea corylifolia was investigated for the first time. The maximum production of daidzein and genistein was achieved when sucrose and maltose used as a sole source of carbon. Suspension cell cultures enriched with sucrose (3%) stimulated accumulation of isoflavones daidzein (1.76% dry wt) and genistein (0.25% dry wt) compared to glucose, fructose and maltose. Sucrose feeding strategy significantly stimulated biomass growth and isoflavones (2.79% dry wt of daidzein and 0.32% dry wt of genistein) production rate. Reduced concentrations of phosphate (0.625 mM) promoted daidzein (1.89% dry wt) and genistein (0.26% dry wt) production by suspension cell cultures, whereas high amount (5mM) in medium was inhibited isoflavones production. It was observed that medium fortified with NH(4)(+) and NO(3)(-) alone inhibited production of isoflavones. The maximum production obtained of daidzein (2.20% dry wt) and genistein (0.29% dry wt) when medium comprised with NH(4)(+)/NO(3)(-) at ratio 20:40 mM as a nitrogen source. Similar nutrient components ratio when altered NH(4)(+)/NO(3)(-); 40:20mM) resulted in approximately 3-fold decrease in production. HPLC analysis revealed that suspension cells cultures leached out trace amount of daidzein and genistein into the culture medium.

Effects of hydrodynamic and interfacial forces on plant cell suspension systems

Plant cells are perceived to be sensitive to the hydrodynamic environment in conventional bioreactors. Heightened sensitivity, relative to most bacterial cultures, is frequently attributed to larger plant cell sizes, extensive vacuolization and aggregation patterns. Early studies of shear sensitivity focused on cell lysis and/or loss of viability. More recently, an extensive array of sub-lethal responses has been identified. A fuller understanding of these sub-lytic effects may assist in the optimization of large-scale cultivation conditions. This paper reviews recent work on the hydrodynamic shear sensitivity of plant cell systems, under cultivation conditions and in purpose-built shearing devices. The relevance of different approaches to the characterization of the intensity of a given hydrodynamic environment is discussed. Indicators of cell response to hydrodynamic stress are evaluated. The potential significance of cellular defense mechanisms, observed in response to mechanical stimulants, is identified.

Plant cell suspension cultures: some engineering considerations

Higher plants are the source of a vast array of biochemicals which are used as drugs, pesticides, flavourings and fragrances. For some of these compounds, plant cell culture can provide a potential production alternative to traditional cultivation methods or chemical synthesis routes. Many systems have been patented and the last 20 years have seen considerable industrial and academic interest in the development of large scale cultures to produce pharmaceutically active, high value substances. However, the industrial application of plant cell suspension cultures has, to date, been limited. Commercialisation has essentially been impeded by economic feasibility, arising from both biological and engineering considerations. This paper reviews the commercial development of the technology to date and focuses on the impact of specific engineering-related factors, in particular, the shear sensitivity of plant cell suspension cultures. Evidence of sensitivity to hydrodynamic shear in bioreactors has generally been attributed to the physical characteristics of the suspended cells. Recent studies indicate that shear sensitivity may not be as important, in some cases, as initially anticipated.