Top 3 tips for bioprocessing success

Tip #1: How to prevent contamination

What is one of the worst things that could go wrong in your laboratory? Ask anyone working to a deadline in a bioprocess laboratory and a likely answer would be contamination of their cultures. Contamination can be hard to trace back to a source and difficult to remove if it is present in your working environment. Fortunately, there are a few simple steps you can follow to minimize the chances of this happening to you.

Avoid contamination of the starter culture

The most frequent cause is contamination of the starter culture. This can happen in many ways: improper handling, poor cleaning or insufficient autoclaving of the culture vessels and reactor or media components. A cleaning and disinfection procedure for laboratory equipment upstream of your bioreactor can help keep contamination from spreading via the seed culture. If contamination is present, an organism that usually grows slowly as a static culture may suddenly find the perfect growth conditions in the bioreactor, quickly overwhelming the other organisms you are actually cultivating. This problem frequently arises in cell cultures, because cells grow very slowly and can be easily flooded by rapidly growing bacteria. One possible solution is to use antibiotics to kill off bacteria.

Reliable steam sterilization of the bioreactor

Maintaining the bioreactor target temperature long enough during the autoclaving process is important to ensure effective sterilization. The temperature sensor of the autoclave should be inserted into the immersion pipe on the culture vessel. For a double-walled culture vessel, there must be enough water present in the jacket to ensure proper heat transfer during sterilization.

Careful assembly of the bioreactor

Assemble the bioreactor carefully and methodically check all seals to help to keep any unwanted visitors from reaching your culture. All sealing rings should be in perfect condition, i.e. there should not be any signs of kinks, flattening or burr formation. If in doubt, it’s better to replace the seal again, especially if it is not seated properly.

Check the O-rings on all components installed on the lid, regardless of whether these are intakes, sensors or plugs.

Special recommendations for cell cultures

• Buy a sterile medium and 70% ethanol for disinfecting.
• Wear gloves
• Work at a sterile bench
• Work with single-use equipment

Lastly, what do you do if contamination does occur?

An occasional lapse can be expected and does not mean your culture is spoiled. However, if you are high levels of contamination over time, this is a good indicator that something needs attention. Following the simple rules provided in this short overview should be enough to reduce the risk of contamination and help your cultures to thrive.

Tip #3: Optimizing protein yield

Optimizing of a bioprocess for protein production is more complex than for simple increase in biomass. Over-production of biomass and normal cell metabolism may limit the amount of cellular resources directed towards making the protein of interest. This short overview lists some of the key points to take into consideration for the best yield of proteins. 

The optimizing of a bioprocess for protein production is more complex than for simple increase in biomass. Over-production of biomass and normal cell metabolism may actually limit the amount of cellular resources directed towards making the protein of interest. A phased approach, with growth being followed by induction of protein manufacture and a change in operating parameters is often best. This change can be triggered at a certain biomass level by a chemical, by a change of feed or a change in a physical parameter such as temperature. The genetic changes made to optimize protein production may adversely affect the cells in terms of growth rates and sensitivity to environmental conditions e.g. heightened shear sensitivity.

The production phase may need careful control of the supply of nutrients to ensure unwanted metabolic pathways are not activated. An example is an excess of glucose leading to alcohol production in some yeasts. The culture conditions must also be maintained in a way which stops any protein produced from being damaged by denaturation or destruction from enzymes released by lysed cells.

These are the key points to take into consideration for the best yield of proteins:

• If the nutrient supply is so excessive that microbial metabolism is only geared towards growth, the microbes will not excrete any metabolites. Managing the bioprocess as a fed-batch process can provide a remedy here. 
• Growth conditions are often not ideal for producing, say, the targeted protein. As a result, you may need to adjust the temperature or the pH to the protein in question in order to improve protein yield and stability.
• Does your strain can produce the desired yields when cultured in this way? Reviewing carefully the literature ahead of time.
• It is just as important to know whether the cultivated strain excretes toxins or growth-inhibiting substances. Those can be produced by growth, by the disintegration of cells or by cell metabolism. These kinds of influencing factors can impair protein production over a period of a few days.