Single –Cell Proteins

The term”single cell proteins” (SCP) refers to the dried cells of microorganisms. These SCPs are produced from cells grown in large- scale culture vats or fermenters. They are then dried and used as protein sources in animal feeds. The use of SCP as a food supplement has a long history. The early Aztecs in Mexico harvested algae from ponds and used them as source of foods.

SCPs have continued to used as human food in certain regions of the world to the present day, however, they have never becomes a major food resource for either humans or domestic animals. Yet SCPs would seem to have tremendous potential as a means to helping feed the world’s hungry. At the very least, SCPs should provide important protein supplements for animal feeds. In Britain, for example, SCP produced from the bacterium Methylophilus methylotrophus is manufactured and sold under the trade name Pruteen for use as an animal feed protein supplements. Similar products have been produced and marketed in Germany and Soviet Union.

With the advent of genetic engineering, SCP would seem to have considerable potential as a means of providing improved nutrition in regions of the world where animal proteins are in short supply in human diets. In addition, SCP should prove to be good alternative to soya bean meal and fish meal as an animal feed protein supplement. The total protein composition of seeds of some of most important agronomic crops provides inadequate amounts of certain amino acids when used as human food. For example, corn seed proteins are very suboptimal amounts of methionine. Thus, SCPs could be used to supplements the lysine and methionine levels in diets based on corn or soybeans, respectively.

Genetic engineering now allows scientists to manipulate bacteria almost at will. In particular, bacteria can be constructed that greatly overproduce a given protein. Up to 50 % of the proteins in a cell may be the product of single gene. This is done by joining the coding sequence of the gene to a strong promoter, inserting the promoter-coding sequence unit into a high- copy number plasmid, and introducing the recombinant plasmid into an appropriate host cell. Some high- copy-number plasmids are present in up to 500 copies per cell. Thus, large amounts of proteins are produced from genes that are available as starting material, and our ability to change codons at wills by site- specific mutagenesis, it should be possible to design bacteria with total proteins (SCPs) of almost any desired amino acid composition. In any case, it will be interesting to see what roles SCPs plays as human food and animal feed supplements in the future.