BIOTECHNOLOGY - V. H. Herasymenko - 2006

Part II. Specialized Biotechnologies

Chapter 19. BIOTECHNOLOGIES FOR L-AMINO ACID PRODUCTION

19.5. BIOTECHNOLOGY FOR L-THREONINE PRODUCTION

One of the most Essential Amino Acids is Threonine, which was discovered and isolated in 1935 during The Study of Fibroin hydrolysates:

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Threonine is synthesized in the Cells of microorganisms and plants, originating from aspartic acid. The Human and Animal bodies cannot biosynthesize threonine. Since plant-based products, which form the staple diet of livestock, contain low amounts of threonine, it must be added to feed. A deficiency of this amino acid in animals leads to fatty Liver, reduced live weight gains, and impaired utilization of Other Amino Acids.

Threonine is also widely used in numerous biotechnological processes. In the pharmaceutical industry, this amino acid is required for The production of certain semi-synthetic Antibiotics. Threonine is added to culture media designed for Cell cultivation.

Threonine can be obtained through various pathways: Hydrolysis of natural Proteins, chemical synthesis from acetaldehyde and Glycine, and microbial production. The first two Methods fail to meet the national economy's demand for this amino acid.

For the microbiological production of threonine, corynebacteria and enterobacteria are used as producers. However, corynebacteria, which intensively produce glutamic acid and Lysine, synthesize threonine at a low rate, making its industrial production unprofitable.

Escherichia coli biosynthesizes threonine from aspartic acid through a series of transformations (Fig. 19.2). Alongside threonine, aspartic acid serves as a precursor for lysine, Methionine, and isoleucine, which under normal conditions are channeled into Protein Synthesis, maintaining low intracellular concentrations.

Industrial threonine overproducers were developed from mutants isolated from the parent E. coli K-12 strain using Introduction/32.html">Genetic Engineering techniques, specifically Gene Amplification. When a gene is replicated multiple times within The Genome, The amount of the product it encodes increases in proportion to the copy number. It has been established for E. coli that the genes encoding the Enzymes responsible for threonine synthesis form the threonine Operon, which contains three genes. Consequently, increasing the number of threonine operons in the E. coli cell ensures a proportional rise in Amino acid synthesis.

Fig. 19.2. Scheme of threonine Biosynthesis

(after V. I. Artamonov, 1989)

The application of this method enabled the derivation of an E. coli strain capable of synthesizing threonine at a rate an order of magnitude higher than that of corynebacteria, the primary amino acid producers. Trials of the resulting threonine in livestock farming confirmed its high quality. When biotechnological threonine was used as a component of culture media, it was found to promote more intensive cell growth compared to chemically synthesized threonine.