Biotechnology and Bioinformatics (1+1)

9.1.3 Whole – cell Bioreactors

Living cells can be viewed as small biochemical reactors of great complexity. Enzymes came from cells. The earliest bioreactors or fermenters were used in the brewing and wine making industries. During the last 65 years, fungal fermentations have been used to make antibiotics, beginning with penicillin. Now, fermentation’s is also extensively used in the developing biotechnological/pharmaceutical industry.

The first major products made by recombinant organisms were :

insulin (Elililly),

tissue plasminogen activator (Genetech), and

 erythropoietin (Amogen).

• The most common organism used in recombinant fermentations is Escherichia coli, a genetically well-characterized bacterium.
• More current areas of research include limitation of protein synthesis by the amount of mRNA in the cells,
• decreasing protease activity in cells to reduce cellular protein degradation,
• manipulation of cells to inhibit inclusion body formation, and
•  development of new vector-host system for the over exploitation of proteins.

Plant, mammalian, and insect cells hold greater potential for the biotechnology industry. However, their complexity has slowed development of industrial processes.

• As many as 25% of today’s pharmaceuticals are extracted from plants naturally grown.
• A most promising area for plant reactors is the production of Taxol, an anticancer drug, recently approved by the US. Food and Drug administration.
• Currently, Taxol is extracted from yew tree bark, but the demand is greater than the amount usually available from the natural source.

Cell cultures derived from insects:

•  a relative new comer to biotechnology, are more complex than plant cells but easier to establish than mammalian derived cell lines.
• A successful experimental system is the baculovirus system. It consists of a strong promotor that allows a cell to make up to 40% of its protein as the target or product protein with practically no cell multiplication.

Many proteins of mammalian origin are not simply products of gene expression they require glycosylation and sometimes other secondary enzymatic processes for biological activity. Since bacteria cannot carry out these conversions, production of such proteins requires mammalian or at least eukaryotic cell lines.

Mammalian cell grow much more slowly than bacteria, are more demanding in terms of media composition, and may require anchorage to solid supports. They are also very sear sensitive and may be suppressed by their own metabolites. It is relatively easier to establish long-lasting or nearly permanent mammalian culture cells using hybridoma cells for the production of monoclonal antibodies. Hybridoma cells do not require anchorage and have as a rule, the longevity of their parent cancer cell lines.

A technology that is still with infancy is the use of transgenic plant and animals to produce proteins.

• The living plant or animal became the “bioreacter”. This technology involves inserting new genetic information in the embryo and having the nontoxic protein expressed by the mature animal.
• One strategy is to have a protein secreted into an animal’s milk. Then the product is simply separated form the rest of the milk constituents.

To optimize production, fermentation processes are usually performed under conditions of controlled

pH,

dissolved oxygen,

agitation, and temperature.

More complicated control strategies involve regulating protein secretion or substrate addition.

New biosensors are being developed to aid in determining the amount of a substrate or product. These sensors include enzyme (used to detect specific products or substrates), bacteria (to determine BOD), Desulfovibrio desulfuricus (to determine sulfur content).