Vitamin B12#biotechnology

         V I T A M I N - B 12

The disease ,pernicious anemia,  characterized by low levels of hemoglobin , decreased number of erythrocytes and neurological manifestations, has been known for several decades. It was in 1926 some workers reported the liver extracts could cure pernicious anemia. The active principle was later identified as vitamin B12, a water soluble B-complex vitamin.

Occurence

Vitamin B₁2 is present in animal tissue at a very low concentration (e.g. 1 ppm in the liver). It occurs mostly in the coenzyme forms methylcobalamin and deoxyadenosylcobalamin. Isolation of vitamin B₁2 from animal tissues is very expensive and tedious.

Chemistry

Vitamin B12 (cyanocobalamin) is a water soluble vitamin with complex structure. The empirical formula of cyanocobalamin is C63H90N14014PCO. The structure of vitamin B12 consists of a corrin ring with a central cobalt atom. The corrin ring is almost similar to the tetrapyrrole ring structure found in other porphyrin compounds e.g. heme (with Fe) and chlorophyll (with Mg).

The corrin ring has four pyrrole units. Cobalt present at the centre of the corrin ring is bonded to the four pyrrole nitrogens. Cobalt also binds to dimethylbenzimidazole and aminoisopropanol. Thus, cobalt atom present in vitamin B12 is in a coordination state of six.

Biosynthesis

VitaminB12 is exclusively synthesized in nature by microorganisms.An outline of the pathway is depicted in figure below.The biosynthesis of vitaminB12 are not yet fully understood.

COMMERCIAL PRODUCTION OF VITAMIN B12

• Vitamin B12 is commercially produced by fermentation.
• It was first obtained by as a byproduct of strptomyces fermentation in the production of certain Antibiotics (streptomycin,chloramphenicol,or neomycin).
• But the yield was very low.
• Later high yielding straisns were developed.
• At present vitaminB12 is entirely produced by fermentation.
• It is estimated that the world's annual production of vitaminB12 is around 15,000 kg.
• High concentrations of vitaminB12 are detected in sewage - sludge solids.this is produced by microorganisms.
• Recovery of vitaminB12 from sewage-sludge was carried out in some parts of United States.
• Unlike most other vitamins ,the chemical synthesis of vitaminB12 is not practicable,since about 20 complicated reaction steps need to be carried out.
• Fermentation of vitaminB12 is the only choice.

Microorganisms and yields of vitaminB12

• Several microorganisms can be developed for the production of vitaminB12 with varying yields.
• Glucose is the most commonly used carbon source.
• The most commonly used microorganisms are propionibacterium freudenreichii, onas denitrificans,Bacillus megateri and streptomyces olivaceous.

Genetically engineered strains for vitamin B12 production

• By employing modern techniques of genetic engineering ,vitamin b12 production can be enhanced.
• A protoplast fusion technique between protaminobacter rubber& rhodopsedomonas spheroids resulted in a hybrid strain called Rhodopsedomonas protamicus.
• This new Strain can produce as high as 135 mg/l of vitamin b12 utilizing carbon source.