Figure 5.

Vitamin B₁₂ sources and microbial interactions in edible plants, mushrooms, and algae. Most plants neither produce nor require B₁₂. Methylotrophys inhabit soil, water, and plants (aerial surfaces of plants) and some of them have B₁₂ biosynthetic pathways. Plant–bacterial interactions play important roles in plant growth. Mushrooms cannot synthesize B₁₂, but B₁₂ found in mushroom fruiting bodies is derived from B₁₂ sources outside the mushrooms, including concomitant B₁₂-synthesizing bacteria. In aquatic environments, phytoplankton–bacterial interactions play important roles in algal growth because half of all algae require B₁₂. Even in phytoplankton or microalgae without a dependence on B₁₂ for growth, B₁₂ accumulates and is used as a cofactor of B₁₂-dependent methionine synthase (MetH).