Single-Use Technology for Microbial Fermentation


Microbial fermentation processes are used for biomanufacturing of various drugs and vaccines, such as hormones, antibody fragments, and pneumococcal vaccine. Stirred-tank fermentors up to 100,000 L scale have traditionally been used in such microbial processes and their success has formed the general engineering foundation and principles of the design of bioreactors. The majority of today’s fermentation processes are performed in bioreactors constructed of traditional materials such as stainless steel. However, there is an increased interest in disposable technology to gain flexibility, save batch change-over time, and minimize cleaning and cleaning validation efforts.

To date, single-use stirred-tank bioreactors for mammalian and insect cell cultures have been successfully used in scales up to 2,000 L working volume and are installed in both clinical and commercial drug manufacturing facilities. However, for bioreactors to be utilized in microbial fermentation some engineering challenges needed to be addressed. For instance, fermentors had to be designed to handle very high metabolic rates and the high oxygen demands of some microbial cultures. By applying general bioengineering principles and designs, high oxygen transfer rates can be achieved also in disposable fermentors. Augmented designs and operational methods compensate for the low heat transfer rates in these systems. Although pressurizable single-use stirred-tank fermentors are within the realm of the technical feasibility, this feature might not be necessary as sufficient oxygen transfer can be achieved through a variety of mechanical and process control designs and techniques.

For more information on the use of single-use in microbial fermentation, please see:
Cell Culture Dish – “Single-use Technology for Microbial Fermentation”

Question 1

Can you tell me whether there would be cost benefit from switching to single-use technology in microbial fermentation and if so, from where?

Equipment utilization will be much greater due to the faster turnover between runs. Single-use avoids post-run CIP, cleanliness validation, sterilization and pressure testing. The risk of cross-contamination is virtually eliminated. The consumption of water in CIP and sterilization is tremendous. Maintenance is almost non-existent by comparison; with no seals, O-rings or gaskets to replace between runs; not mechanical seals service, etc.

Question 2

What kind of volume do you think single-use can support in microbial fermentation?

This will depend on the process. We have customers running fermentation at 1000L today. We evaluate all such cases individually to be certain of the applicability of single-use fermentors. Mainstream application of single-use fermentation, however, ranges between 50L and 500L; with 500L being an upper boundary right now.

Question 3

Is there technology to support a fully single-use system for microbial fermentation? I mean are there any parts that still need to be cleaned validated?

With respect to the process contacting parts, which is the bioreactor/fermentor bag, there is nothing to clean as nothing gets reused from that assembly. This is one of the main benefits of single-use bioprocess technology as a whole. And, specifically, for fermentation, single-use technology eliminates cross-contamination previously associated with O-rings, gaskets, diaphragms and mechanical seals. The process piping from the stainless steel equivalent has been replaced by elastomeric tubing. No cleaning necessary, just discard similar to other process waste.

Question 4

It seems that single-use is a good option for new processes, but for existing processes what points would you consider when deciding whether to change to single-use?

Single-use technology is a good option for new and existing processes. There may be more to evaluate for existing processes because is it already operational. Consider that single-use technology shortens the turnaround time thereby, effectively, increasing equipment utilization. The industry remains very competitive and saving time had direct benefit to the bottom line. Also consider the amount of time and, if nothing else, the water associated with cleaning a fermentor between runs. Water is a valuable resource with daily headlines trumpeting its scarcity. Consider, too, footprint…and not just the footprint at the fermentor. Single-use fermentors do no rely on piping skid adjacent to the vessel; nor do they require clean or plant steam sources.

Question 5

Are there any vaccine targets that you would not want to manufacture using single-use systems maybe a highly infectious/toxic target or some other factor? Are there any special conditions that should be considered?

Application of single-use technology does not relieve the process owner from assessing any and all appropriate risks. The infectiousness or toxicity of a process, process intermediate or end-product should be considered, with operator safety being paramount. Unlike stainless steel fermentors, single-use fermentors rely on plastic films, tubing, etc. There are risks, though low, of breaches in the integrity of the film or tubing or failures due to miss use.

Question 6

We are looking to manufacture a few different products mammalian and microbial in the same location. We have looked at a few of the flexible facility models for mammalian cell culture. Do you believe that a similar approach using single-use in microbial fermentation and single-use for mammalian would be effective? If so, are there any aspects of planning that you would recommend considering?

Very definitely…the flexibility imparted to fermentation, like in cell culture, is analogous. If I interpret your question further, might I also say that dual-purpose systems, systems capable of either cell culture or fermentation by switching reactor bags and some accessories are available. This type of dual-purpose product provides another level of flexibility, especially for development and pilot operations. With respect to implementing a flexible manufacturing environment, a comprehensive approach to the owner’s business is recommended, if not required. Single-use technology provide a catalyst for implementing changes necessary to be competitive today and into the future where biologics production is concerned. Single-use technology suppliers, especially for the unit operations become a much deeper “partner” in the business. The more information that can be shared, the better the supplier is able to support business continuity, for things like facility layout/design, operational efficiency, supply chain integration, just-in-time materials delivery and many more. As mentioned in an earlier topic response, footprint, utility requirement and water consumption all change for the better. Personnel skills and training may need augmentation. The technology really provides an excellent opportunity to align a manufacturing entity with specifics of today’s biomolecule while equipping them with ability to handle the changes so often associated with our industry.

Question 7

In single use microbial applications how would you recommend addressing the challenges of low oxygen transfer and cooling issues that have been discussed?

In steam sterilizable, or conventional fermentors, we have had the ability to deliver more horsepower to the agitation system and oxygen to the sparging system than was sometimes needed; an overabundance of capacity, at times. With single-use fermentors, efficiency, especially in the process is the premium. Single-use fermentors are capable of controlling dissolved oxygen with the typical cascade control elements: air & oxygen gas flow, agitation and substrate feed. Pressure is all that is missing. Gas flow rates between 1 and 2 vessel volumes per minute are available. And, with agitation systems equipped with one or more Rushton impellers capable of supporting oxygen transfer rates in the 500-1100 range, single-use fermentor performance is comparable to conventional fermentors. Ensuring sufficient cooling to handle metabolic heat loads while overcoming the insulative properties of the bag film has been achieved. Like the application of technology in any area, there are boundaries. Within those boundaries, or design space, the user obtains the associated benefits. Necessity will help push and expand current boundaries.

Question 8

Have you tried this technology with E. coli fermentations both batch and fed batch? Did you have any advice on using this technology with E. Coli

Batch an fed-batch processes have been run with success. Be sure culture media is filter sterilizable. As with the application of any new technology, training and familiarity will ease the transition.

Question 9

How would you recommend testing scale up conditions prior to moving to the single use bioreactor? Are there any differences to be aware of between using single use and stainless steel?

Simulated process modeling, using current known process data typically provides the necessary feasibility information. About the technologies, for processes that are transferable, single-use offers an equivalent platform to stainless. There may be unique processes not suited for single-use. Media and additives cannot be sterilized in the bag, but rather externally. Consider your motivation for implementing single-use fermentor technology. Outline your process and go through it, on paper, to maximize your success. Planning and preparation is crucial, especially considering how quickly a system can be turned around. Single-use fermentors can play an essential role in modern-day process environments...development and production.

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