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Vitamin B12 synthesis by human small intestinal bacteria


In man, physiological amounts of vitamin B12 (cyanocobalamin) are absorbed by the intrinsic factor mediated mechanism exclusively in the ileum1. Human faeces contain appreciable quantities of vitamin B12 or vitamin B12-like material presumably produced by bacteria in the colon2, but this is unavailable to the non-coprophagic individual. However, the human small intestine also often harbours a considerable microflora3–6 and this is even more extensive in apparently healthy southern Indian subjects6. We now show that at least two groups of organisms in the small bowel, Pseudomonas and Klebsiella sp., may synthesise significant amounts of the vitamin.

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Albert, M., Mathan, V. & Baker, S. Vitamin B12 synthesis by human small intestinal bacteria. Nature 283, 781–782 (1980).

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