Fluid dynamic conditions and oxygen availability effects on microbial cultures in STBR: An overview

Effects of LEDs, macronutrients and culture conditions on biomass and artemisinin production using Artemisia annua L. suspension cultures

Artemisinin is a sesquiterpene lactone extracted from the medicinal plant Artemisia annua L. (sweet wormwood). It has traditionally been utilized in artemisinin-based combination therapies (ACTs) for the malarial parasite, including drug-resistant strains. Natural artemisinin extraction is costly with low yields. Due to its effectiveness, there is a significant rise in the demand for artemisinin production. In vitro cell suspension culture offers a cost-effective and viable technique for artemisinin production. Therefore, this study aimed to optimize a protocol for cell suspension culture of A. annua L. to enhance biomass and artemisinin production. A successful cell suspension culture was initiated from induced callus. The highest cell biomass was obtained in suspension cultures grown with an initial inoculum size of 0.1 g of mixed type cell aggregates, in media with a pH of 6.2 and a rotation speed of 90 rpm. Macronutrient concentrations influenced both biomass and artemisinin content, with optimal biomass achieved at 19 mM KNO3 and 1.56 mM KH2PO4. The absence of these nutrients resulted in the highest artemisinin levels. Different LED wavelengths also significantly influenced biomass and artemisinin production. Red + blue LED increased cell biomass, while the highest artemisinin content was observed under red LED. The upscaling of the culture indicated a variation in biomass yield pattern, but the highest growth index was achieved in the 500 mL Erlenmeyer flask. This study successfully established a cell suspension culture for A. annua L., demonstrating the influence of macronutrients and red LED on biomass and artemisinin production, providing insights for potential large-scale production.

Zeaxanthin Production by an Antarctic Flavobacterium sp.: Effect of Dissolved Oxygen Concentration and Modeling Kinetics in Batch and Fed-Batch Fermentation

Zeaxanthin is a high-value carotenoid, found naturally in fruits and vegetables, flowers, and microorganisms. Flavobacterium genus is widely known for the production of zeaxanthin in its free form. Nowadays, the production of zeaxanthin from bacteria is still noncompetitive with traditional methods. The study of different operational conditions to enhance carotenoid production, along with the development of better models, is critical to improve the optimization, prediction, and control of the bioprocess. In this work, the influence of dissolved oxygen concentration was studied on zeaxanthin, β-cryptoxanthin, and β-carotene production. It was found that 10% pO2 was the best condition for zeaxanthin production in a batch bioprocess, reaching a total carotenoid concentration of 3280 ± 88 μg/L, with 86% of zeaxanthin. To enhance carotenoid production, a fed-batch culture was performed. Although biomass and total carotenoid productivity were similar between batch and fed-batch processes, the total carotenoid concentration in the fed-batch was the highest (8.3 mg/L) but with lower zeaxanthin content and productivity. Two kinetic models were proposed based on a modified Monod and Luedeking-Piret model, as well as glucose, biomass, oxygen, and each carotenoid concentration mass balance. The binary model that considers oxygen in biomass growth and product formation presented a better fit to the experimental data.

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.

Development of a Simple and Robust Kinetic Model for the Production of Succinic Acid from Glucose Depending on Different Operating Conditions

Succinic acid (SA) is one of the main identified biomass-derived chemical building blocks. In this work we approach the study of its production by Actinobacillus succinogenes DSM 22257 from glucose, focusing on the development and application of a simple kinetic model capable of representing the evolution of the process over time for a great diversity of process variables key to the production of this platform bio-based chemical: initial biomass concentration, yeast extract concentration, agitation speed, and carbon dioxide flow rate. All these variables were studied experimentally, determining the values of key fermentation parameters: titer (23.8–39.7 g·L−1), yield (0.59–0.72 gSA·gglu−1), productivity (0.48–0.96 gSA·L−1·h−1), and selectivity (0.61–0.69 gSA·gglu−1). Even with this wide diversity of operational conditions, a non-structured and non-segregated kinetic model was suitable for fitting to experimental data with high accuracy, considering the values of the goodness-of-fit statistical parameters. This model is based on the logistic equation for biomass growth and on potential kinetic equations to describe the evolution of SA and the sum of by-products as production events that are not associated with biomass growth. The application of the kinetic model to diverse operational conditions sheds light on their effect on SA production. It seems that nitrogen stress is a good condition for SA titer and selectivity, there is an optimal inoculum mass for this purpose, and hydrodynamic stress starts at 300 r.p.m. in the experimental set-up employed. Due to its practical importance, and to validate the developed kinetic model, a fed-batch fermentation was also carried out, verifying the goodness of the model proposed via the process simulation (stage or cycle 1) and application to further cycles of the fed-batch operation. The results showed that biomass inactivation started at cycle 3 after a grace period in cycle 2.

Extended batch cultures for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) production by Azotobacter vinelandii OP growing at different aeration rates

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a polymer produced by Azotobacter vinelandii OP. In the bioreactor, PHBV production and its molar composition are affected by aeration rate. PHBV production by A. vinelandii OP was evaluated using extended batch cultures at different aeration rates, which determined different oxygen transfer rates (OTR) in the cultures. Under the conditions evaluated, PHBV with different 3-hydroxyvalerate (3HV) fractions were obtained. In the cultures with a low OTR (6.7 mmol L-1 h-1, at 0.3 vvm), a PHBV content of 38% w w-1 with 9.1 mol % 3HV was achieved. The maximum PHBV production (72% w w-1) was obtained at a high OTR (18.2 mmol L-1 h-1, at 1.0 vvm), both at 48 h. Thus, PHBV production increased in the bioreactor with an increased aeration rate, but not the 3HV fraction in the polymer chain. An OTR of 24.9 mmol L-1 h-1 (at 2.1 vvm) was the most suitable for improving the PHBV content (61% w w-1) and a high 3HV fraction of 20.8 mol % (at 48 h); and volumetric productivity (0.15 g L-1 h-1). The findings indicate that the extended batch culture at 2.1 vvm is the most adequate mode of cultivation to produce higher biomass and PHBV with a high 3HV fraction. Overall, the results have shown that the PHBV production and 3HV fraction could be affected by the aeration rate and the proposed approach could be applied to implement cultivation strategies to optimize PHBV production for different biotechnological applications.

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

The large-scale production of plant-derived secondary metabolites (PDSM) in bioreactors to meet the increasing demand for bioactive compounds for the treatment and prevention of degenerative diseases is nowadays considered an engineering challenge due to the large number of operational factors that need to be considered during their design and scale-up. The plant cell suspension culture (CSC) has presented numerous benefits over other technologies, such as the conventional whole-plant extraction, not only for avoiding the overexploitation of plant species, but also for achieving better yields and having excellent scaling-up attributes. The selection of the bioreactor configuration depends on intrinsic cell culture properties and engineering considerations related to the effect of operating conditions on thermodynamics, kinetics, and transport phenomena, which together are essential for accomplishing the large-scale production of PDSM. To this end, this review, firstly, provides a comprehensive appraisement of PDSM, essentially those with demonstrated importance and utilization in pharmaceutical industries. Then, special attention is given to PDSM obtained out of CSC. Finally, engineering aspects related to the bioreactor configuration for CSC stating the effect of the operating conditions on kinetics and transport phenomena and, hence, on the cell viability and production of PDSM are presented accordingly. The engineering analysis of the reviewed bioreactor configurations for CSC will pave the way for future research focused on their scaling up, to produce high value-added PDSM.

Molecular weight and guluronic/mannuronic ratio of alginate produced by Azotobacter vinelandii at two bioreactor scales under diazotrophic conditions

Alginates can be used to elaborate hydrogels, and their properties depend on the molecular weight (MW) and the guluronic (G) and mannuronic (M) composition. In this study, the MW and G/M ratio were evaluated in cultures of Azotobacter vinelandii to 3 and 30 L scales at different oxygen transfer rates (OTRs) under diazotrophic conditions. An increase in the maximum OTR (OTR_max) improved the alginate production, reaching 3.3 ± 0.2 g L^-1. In the cultures conducted to an OTR of 10.4 mmol L^-1 h^-1 (500 rpm), the G/M increased during the cell growth phase and decreased during the stationary phase; whereas, in the cultures at 19.2 mmol L^-1 h^-1 was constant throughout the cultivation. A higher alginate MW (520 ± 43 kDa) and G/M ratio (0.86 ± 0.01) were obtained in the cultures conducted at 10.4 mmol L^-1 h^-1. The OTR as a criterion to scale up alginate production allowed to replicate the concentration and the alginate production rate; however, it was not possible reproduce the MW and G/M ratio. Under a similar specific oxygen uptake rate (qO₂) (approximately 65 mmol g^-1 h^-1) the alginate MW was similar (approximately 365 kDa) in both scales. The evidences revealed that the qO₂ can be a parameter adequate to produce alginate MW similar in two bioreactor scales. Overall, the results have shown that the alginate composition could be affected by cellular respiration, and from a technological perspective the evidences contribute to the design process based on oxygen consumption to produce alginates defined.