Metabolic engineering

Cellular metabolism can be optimized for industrial use.

Metabolic engineering is the practice of optimizing genetic and regulatory processes within cells to increase the cells' production of a certain substance. Metabolic engineers commonly work to reduce cellular energy use (ie, the energetic cost of cell reproduction or proliferation) and to reduce waste production. Producing beer, wine, cheese, pharmaceuticals, and other biotechnology products often involves metabolic engineering.

Cells are complex systems; genetic and regulatory changes can have drastic effects on the cells' ability to survive. Therefore, trade-offs become apparent during metabolic engineering.

In addition to directly deleting and/or overexpressing the genes that encode for metabolic enzymes, the current focus is to target the regulatory networks in a cell to efficiently engineer the metabolism^[1].

Decreasing cellular energy use

Metabolic engineering can be useful in industry. Certain industries use cells to create useful products. Producing the greatest number of those cells is a sought-after goal. The only known method of production, however, may involve oxidizing of carbon compounds. The carbon compounds may be in limited supply. Therefore, engineering cells to reproduce or proliferate more rapidly given the same amount of carbon compounds would mean greater industrial efficiency.

E. coli genes were added to the M. methylotrophus genome.

The role of Methylophilus methylotrophus in the animal feed industry is an example. M. methylotrophus uses methanol to produce certain proteins used in animal feed. Producing greater masses of proteins using the same mass of methanol would increase efficiency. Windass, et al. (1980) accomplished this by silencing genes in M. methylotrophus and inserting genes from E. coli. This example of metabolic engineering resulted in an organism capable of using a lesser mass of adenosine triphosphate to produce the same mass of glutamate.

Metabolic pathway manipulation

Cameron and Tong (1993), classified the metabolic pathway manipulation in five groups, i.e., application aiming at

1. Yield and Productivity improvement of products made by microorganisms.
2. Expansion of the range of the substrate that can be metabolized by an organism.
3. Formation of new and novel products.
4. General improvements in cellular properties.
5. Xenobiotic degradation.

Metabolic pathway synthesis

Metabolic pathway synthesis deals with the construction of stoichiometrycally consistent routes of biochemical (enzyme catalyzed) reactions that meet certain specification. There are various types of specifications that can be formulated according to the role of metabolites and and bio-reactors in metabolic pathways.

Metabolic Flux Analysis

Degrees of Freedom

                                       F=J-K

J: Number of metabolites K: Number of reactions F:Degree of freedom

Condition 1: If F= Number of flux measured, then the system becomes determined. Condition 2: If F< Number of flux measured, then the system becomes overdetermined. Condition 3: If F> Number of flux measured then the system becomes underdetermined.

• For determined systems:

           vc = (GcT )-1 GmTvm

• For overdetermined systems:

          vc = (GcT )# GmTvm

          where,(GcT )# =(GcGcT )Gc

• For underdetemined systems:

          Linear programming is used to find the optimal (maximal or minimal) solution for given objective function.

References

• Stephanopoulos, G. N., Aristidou, A. A., Nielsen, J. (1998). "Metabolic Engineering: Principles and Methodologies". San Diego: Academic Press.
• Vemuri, G.N. and Aristidou, A. A. (2005). Metabolic Engineering in the -omics Era: Elucidating and Modulating Regulatory Networks. Microbiol. Mol. Biol. Rev. 69(2):197-216.
• Domach, M. M. (2004). Introduction to biomedical engineering. Upper Saddle River: Pearson Prentice Hall.
• Windass, J. D. & Worsey, M. J. & Pioli, E. M. & Pioli, D. & Barth, P. T. & Atherton, K. T. & Dart, E. C. & Byrom, D. & Powell, K. & Senior, P. J. (1980). Improved conversion of methanol to single-cell protein by Methylophilus methylotrophus. In Nature, 287, 396 – 401.

1. ^ [1] http://mmbr.asm.org/cgi/content/full/69/2/197

See also

• Bioreactor
• Bacterial transformation
• Genetic engineering