Vitamin B12 (cyanocobalamin) contains a molecule of cobinamide linked to a nucleotide which has 5,6-dimethyl benziminazole as its base, instead of a purine or pyrimidine base (Fig. 15.1). The cobinamide molecule has a central atom of cobalt linked to a cyanide group and surrounded by four reduced pyrol rings joined to form a macroring. A number of carbon atoms carry methyl or other substituent group (Riviere, 1977).
Commercially vitamin B12 is produced in a continuous culture, where two fermenters are used in a series. In each fermenter culture is kept for about 60 hours. Precaution taken is that the first fermenter should be anaerobic, while the second aerobic one. In the second fermenter 5,6-dimethyl benziminazol is added continuously.
Sterilized culture medium, containing glucose, corn steep, betain (5%), cobalt (5 ppm) and pH 7.5 in fermenter, is inoculated with Propionibacterium freudenreichii and allowed to anaerobic fermentation for about 70 hours. During this period cobinamide is produced which accumulates in the broth. Thereafter, 5,6-dimethyl benziminazole (0.1%) is added to it. The fermenter is then kept further for 50 hours for aerobic fermentation.