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FBS-Foetal Bovine Serum

FBS-Foetal Bovine Serum


Foetal Bovine Serum (FBS) has been described as: “the most universally applicable cell culture additive for the stimulation of cellular proliferation.” It is certainly one of the most universal growth media for cell culture.  It is obtained from foetal bovine blood which has been allowed to clot. The raw serum is separated and quickly frozen for storage. It is also more commonly known in some parts of the world as Fetal Calf Serum or FCS.

The exact composition of FBS is still unclear, therefore its precise function in cell culture is yet to be fully determined. But in general, it is known to contain certain dissolved nutrient substances. These are roughly as follows:

Nutrients and Metabolites are present in the form of free fatty acids, ketone bodies and glucose. There are several other intermediary metabolites present. Essential minerals and trace elements can also be found in the form of potassium, sodium, calcium and chloride ions. Several trace elements are also present, such as iron, copper and zinc ions.

There are several different transport proteins present such as albumin. Fibronectin has also been found in FBS. This is thought to be needed for cell adhesion to the matrix. As well as these, there are several enzymes and growth factors such as epidermal growth factor and fibroblast growth factor.  There are also growth inhibition factors and hormones present. Some of these include follicle stimulating hormone, insulin and steroid hormones such as hydrocortisone, cortisol and testosterone.

FBS is often used in preference to other nutrient solutions when there are sensitive cells, or certain cell cultures which require more nutrition. It is used at concentrations of between 5 and 20% for maximum efficacy. Its use with each cell line must be tested for optimal working concentration.

It is stable at room temperature but long term storage is at -20oC. It is usually aliquoted into workable quantities depending on how often it is required in freezable vials or bottles. Usually laboratory freezers are able to maintain their set temperature and care must be taken that a frost-free freezer is not used for long term storage as the continual freezing, thawing cycle fluctuates the temperature too much for the solution to remain viable.

Thawing from frozen is done slowly, usually in a refrigerator at 2-4oC overnight if time allows. This slow thawing is the best way to preserve the large proteins in suspension within the medium. Thawing is completed at room temperature. 

If rapid thawing is required, then it is possible to do this in a water bath set to 37oC. In this case, a shaking water bath is the best to use. If this is not possible, then the serum can be swirled during thawing. If a colour gradient, or precipitate is seen present in the serum, then it has been insufficiently mixed during thawing. This means that the high molecular weight lipids and proteins present in the FBS have precipitated out of solution. 

In the worst cases of this, these precipitates may form an insoluble layer at the bottom of the vial. A small amount of precipitate may re-dissolve with more mixing, but if the process has gone too far, then the insoluble layer will remain. This cannot be removed by filtration, which could actually remove some of the nutrient properties.