Fermentation and biotechnological production: complete guide to upstream bioprocessing
Micro-organisms and cell lines as production platforms
Upstream bioprocessing selects the most suitable production platform based on the desired product, the required post-translational modifications and the production titre. Escherichia coli is the most widely used bacterial expression system due to its rapid growth of 0.3 to 1.0 hour generation time, well-understood genetics and high production titre of over 50 g/L inclusion bodies. Saccharomyces cerevisiae and Pichia pastoris are suitable yeast expression systems for proteins requiring secretion or N-glycosylation, with titres of 3 to 10 g/L for simple proteins. Mammalian cell lines, with CHO (Chinese Hamster Ovary) as the dominant choice for more than 70% of approved biologics, offer correct human-like glycosylation for therapeutic proteins. Insect cell systems Sf9 and High Five via baculovirus infection and transient expression systems offer flexibility for small batches and rapid titre improvement in the early development phase. The production platform directly determines the upstream and downstream processing strategy across the full life cycle of the drug.
Bioreactor design and mixing
Bioreactor design is critical for controlling the cells' environmental conditions and optimising the mass transfer of oxygen and carbon dioxide. Stirred tank reactors (STR) are the most widely used bioreactor type in pharmaceutical production, with working volumes from 2 to over 25,000 litres, fitted with Rushton turbine or marine propeller impellers at an impeller-to-vessel diameter ratio of 1:3. The bioreactor's volumetric oxygen transfer coefficient (kLa) determines the maximum oxygen supply capacity of the culture: for CHO cells with a specific oxygen consumption qO2 of 1 to 10 mmol O2/g·h, a kLa of 2 to 20 h⁻¹ is required. Airlift bioreactors without mechanical agitation use air or gas bubbles for mixing and are suitable for shear-sensitive cell lines, where the Kolmogorov length scale of turbulence must remain above the cell diameter of 10 to 20 micrometres. Disposable bioreactors made from single-use materials offer advantages for clinical batch production: no cleaning, elimination of cross-contamination and faster turnaround between batches of 4 to 6 hours versus 48 to 72 hours for stainless steel.
Fed-batch and continuous fermentation
Fed-batch cultivation is the dominant process mode in pharmaceutical bioproduction and combines the benefits of high cell concentration with controllable product formation via a guided feed addition protocol. The fed components, typically glucose, amino acids and vitamins, are dosed based on online measurements of the glucose concentration below 1 g/L via enzymatic or NIR sensors to avoid overfeeding and catabolite repression. Fed-batch CHO cell cultures reach cell concentrations of 50 to over 100 million cells per mL and monoclonal antibody titres of 3 to over 10 g/L over process durations of 12 to 21 days. Continuous fermentation via perfusion culture circulates cell retention through a spin filter or alternating tangential flow filtration (ATF), with cell concentrations up to 200 million cells per mL and day-for-day productivity up to 3 times higher than fed-batch. Intensified bioprocessing via N-1 perfusion at the seed fermentation stage compensates for the longer start-up phase of production bioreactors and increases the facility's total annual productivity by 25 to 50%.
Process control: pH, DO and glucose
Process control in bioreactors monitors and regulates critical process parameters that directly affect cell growth and product formation via closed-loop control strategies. Dissolved oxygen (DO) control via a cascade controller to impeller speed and air supply maintains oxygen saturation between 30 and 50% of air saturation for optimal aerobic CHO cell culture; under-saturation below 20% causes metabolic stress and reduced productivity. pH control via addition of sodium carbonate solution or CO2 gassing maintains pH within 0.05 units of the setpoint of 6.95 to 7.20, depending on the cell line and desired metabolic profile. Glucose concentration measurement via an online YSI analyser or enzymatic flow cell with a response time of 5 to 15 minutes drives the fed-batch feed pumps and prevents glucose limitation at concentrations below 0.5 g/L. Process analytical technology (PAT) via online dielectric spectroscopy biomass sensor provides direct measurement of viable cell concentration every 15 seconds without sampling loss, enabling continuous process optimisation.
Bioreactor scale-up
Scaling up from 2-litre lab scale to 200-litre pilot scale and 10,000-litre commercial scale requires preserving critical bioprocess parameters via dimensionless numbers and specific scaling criteria. Equal specific mixing or power input per volume (P/V) of 50 to 200 W/m³ is a common scaling criterion that ensures the turbulent micro-scale stays above the cell diameter to limit shear stress. Gas sparging via injection nozzles and ring spargers must be scaled based on equal gas holdup fraction, which amounts to 0.01 to 0.05 v/v, measured via the pressure differential method. Heat transfer calculations for biological heat generation (qheat) of 50 to 200 kW/m³ determine the cooling water requirements of the jacketed bioreactor at production scale. Volumetric production time (PT) of the bioreactor, defined as the annual production hours divided by the working volume, is a key parameter for comparing the economic efficiency of different bioreactor formats at comparable capital and operational costs.
Conclusion
Upstream bioprocessing is the technological foundation for the production of biologics, monoclonal antibodies and biotechnological medicines that are transforming the pharmaceutical industry. Hecht Technology provides expertise in bioreactor design, process control implementation, fed-batch optimisation and scale-up for biotechnological production processes. Contact us for support with your upstream bioprocessing project.
What do industrial fermentation facilities and GMP qualification cost?
Investment in a fermentation facility typically consists of CapEx (bioreactor, HVAC, sterilisation, monitoring, utilities) of approximately 1 to 5 million euros, OpEx of 500,000 to 2 million euros per year, and GMP validation costs of 200,000 to 1 million euros. For biologics with an annual market of 5 to 20 million euros, ROI is typically 3 to 5 years. Incremental scale-up — pilot, clinical, commercial — spreads the investment risk across the development phases.
Hecht Technology: single-use and containment in bioprocessing
Modern upstream bioprocessing increasingly employs single-use technology to prevent cross-contamination between batches and reduce validation time. Hecht Technology's single-use isolator supports this for contained transfer and sampling of biomass and media, while our columns and process towers are used for downstream separation and purification steps after fermentation.