which vitamin is produced by bacteria in the colon
B is produced in nature only by some prokaryotes (certain bacteria and archaea); it is not made by any multicellular or single-celled eukaryotes. It is synthesized by some gut bacteria in humans and other animals, but humans cannot absorb the B made in their guts, as it is made in the colon which is too far from the small intestine, where absorption of B occurs. Ruminants, such as cows and sheep, absorb B produced by bacteria in their guts. For gut bacteria of ruminants to produce B the animal must consume sufficient amounts of cobalt.