Vitamin B₁₂sources and microbial interaction

Vitamin B₁₂ is synthesized only by certain bacteria and archaeon, but not by plants. The synthesized vitamin B₁₂ is transferred and accumulates in animal tissues, which can occur in certain plant and mushroom species through microbial interaction. In particular, the meat and milk of herbivorous ruminant animals (e.g. cattle and sheep) are good sources of vitamin B₁₂ for humans. Ruminants acquire vitamin B₁₂, which is considered an essential nutrient, through a symbiotic relationship with the bacteria present in their stomachs. In aquatic environments, most phytoplankton acquire vitamin B₁₂ through a symbiotic relationship with bacteria, and they become food for larval fish and bivalves. Edible plants and mushrooms rarely contain a considerable amount of vitamin B₁₂, mainly due to concomitant bacteria in soil and/or their aerial surfaces. Thus, humans acquire vitamin B₁₂ formed by microbial interaction via mainly ruminants and fish (or shellfish) as food sources. In this review, up-to-date information on vitamin B₁₂ sources and bioavailability are also discussed. Impact statement To prevent vitamin B₁₂ (B₁₂) deficiency in high-risk populations such as vegetarians and elderly subjects, it is necessary to identify foods that contain high levels of B₁₂. B₁₂ is synthesized by only certain bacteria and archaeon, but not by plants or animals. The synthesized B₁₂ is transferred and accumulated in animal tissues, even in certain plant tissues via microbial interaction. Meats and milks of herbivorous ruminant animals are good sources of B₁₂ for humans. Ruminants acquire the essential B₁₂ through a symbiotic relationship with bacteria inside the body. Thus, we also depend on B₁₂-producing bacteria located in ruminant stomachs. While edible plants and mushrooms rarely contain a considerable amount of B₁₂, mainly due to concomitant bacteria in soil and/or their aerial surfaces. In this mini-review, we described up-to-date information on B₁₂ sources and bioavailability with reference to the interaction of microbes as B₁₂-producers.