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Biotechnology Homework Help: Biotransformation

When an organic compound is modified by simple chemically defined reactions, catalyzed by enzymes present in cells, into a product that is recoverable, it is called biotransformation. Both the substrate and product are not involved in the primary or secondary metabolism of the organism employed. This is in contrast to the various metabolites, e.g. organic acids, amino acids, antibiotics etc. produced by the complex pathways of primary or secondary metabolism of the organism. Biotransformations are performed by microbes, plant cells as well as animal cells. But microbial process is far more efficient economical due to the rapid microbial growth and high metabolic rates of micro-organisms.

The inoculum

Vegetative cells, resting cells, dried cells, spores, or immobilized cells as agents of biotransformation. According to home work helper the micro-organisms used for biotransformations are selected by primary screening of culture collections or from among isolates obtained from nature. The selected organisms are subjected to strain improvement, and mutants deficient in specific enzymes are often isolated to prevent undesirable modification of the product.

According to studydaddy the microbes used for biotransformation are eubacteria, streptomycetes and fungi; their cultures are usually maintained in frozen state at -20 to -170˚C. The inoculum is developed in stages as with other fermentation operations.

The incubation

The inoculum is transferred into a fermenter and conditions for optimal growth are provided. When the desired cell density is achieved, the substrate is added to the fermenter broth and incubated for 2-5 days. Substrates insoluble in water, e.g. steroids may be added as follows: (i) dissolved in a water-miscible organic solvent like ethanol, methanol, acetone etc. (solution added slowly with vigorous agitation), (ii) suspended in a surfactant, e.g. Tween 80, as fine particles, or (iii) as a fine powder.

Alternatively the cells may be separated from the broth by filtration or centrifugation, washed and suspended in a suitable buffer. The substrate, e.g. a steroid, is added into the buffer, this simplified recovery and purification of the product. Yet another approach uses cells/mycelium immobilized on a solid support which is then packed in a column. The substrate is passed through the column to allow biotransformation.


Commercial examples

Conversion of wine into vinegar was practiced in Babylon as early as 5000 BC; in 1864, Pasteur showed the role of microbes in the process. By 1900, several bioconversions, e.g. ethanol to acetic acid, glucose to gluconic acid, fructose to mannitol, tannin to gallic acid etc. were known. But the first biotransformation to be commercialized was conversion of deoxycorticosterone into corticosterone by ox adrenals. But this bioconversion is now achieved by much more efficient microbial process.

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