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Letters
Nature 283, 781 - 782 (21 February 1980); doi:10.1038/283781a0

Vitamin B12 synthesis by human small intestinal bacteria

M. J. Albert, V. I. Mathan & S. J. Baker*

Wellcome Research Unit, Christian Medical College Hospital, Vellore-632004, Tamil Nadu, India
*Present address: Department of Medicine, University of Manitoba, 409 Tache Avenue, Winnipeg, Manitoba R2H 2A6, Canada.

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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