Neither plants nor animals are independently capable of constructing vitamin B12.[41] Only bacteria and archaea[42] have the enzymes required for its synthesis. The total synthesis of B12 was reported by Robert Burns Woodward[43] and Albert Eschenmoser in 1972,[44][45] and remains one of the classic feats of organic synthesis. Species from the following genera are known to synthesize B12: Acetobacterium, Aerobacter, Agrobacterium, Alcaligenes, Azotobacter, Bacillus, Clostridium, Corynebacterium, Flavobacterium, Lactobacillus, Micromonospora, Mycobacterium, Nocardia, Propionibacterium, Protaminobacter, Proteus, Pseudomonas, Rhizobium, Salmonella, Serratia, Streptomyces, Streptococcus and Xanthomonas.
Industrial production of B12 is through fermentation of selected microorganisms.[46] Streptomyces griseus, a bacterium once thought to be a yeast, was the commercial source of vitamin B12 for many years.[47][48] The species Pseudomonas denitrificans and Propionibacterium shermanii are more commonly used today.[49] These are frequently grown under special conditions to enhance yield, and at least one company, Rhône-Poulenc of France, which has merged into Sanofi-Aventis, used genetically engineered versions of one or both of these species. Since a number of species of Propionibacterium produce no exotoxins or endotoxins and are generally regarded as safe (have been granted GRAS status) by the Food and Drug Administration of the United States, they are presently the FDA-preferred bacterial fermentation organisms for vitamin B12 production.[50]
The total world production of vitamin B12, by four companies (the French Sanofi-Aventis and three Chinese companies) is said to have been 35 tonnes in 2008.[51] Most of this production is used as an additive to animal feed.[52][citation needed]
See cyanocobalamin for discussion of the chemical preparation of reduced-cobalt vitamin analogs and preparation of physiological forms of the vitamin such as adenosylcobalamin and methylcobalamin.
( تقرير عن مشاركة سيئة )، و الموجودة أسفل كل مشاركة .
2013-01-15, 22:53
quelle sont les bactéries qui synthése la vit b12
العرض العادي
