Vitamin B12, or cobalamin, is structurally one of the most complex non-polymer molecules in human biology. It is absolutely essential for the healthy functioning of our nervous system, the formation of red blood cells, and the synthesis of DNA. However, there is a fundamental quirk in its biological origin: neither plants nor animals possess the genetic blueprint to manufacture it. In the entirety of the natural world, cobalamin is synthesized exclusively by a select group of bacteria and archaea.