Nat. Microbiol. https://doi.org/10.1038/s41564-019-0469-7 (2019)

An enzyme found in a bacterium in the human gut microbiome is able to convert blood type A into the universal donor blood type O.

Red blood cells are defined on the basis of the carbohydrate antigens on their cell surface. Blood type A contains antibodies against blood type B, and vice versa. There may be lethal consequences if the wrong blood type is donated. Blood type O has none of these antigens and can be transfused between individuals with the same rhesus type. A large supply of this type of blood is needed for emergencies.

A group of scientists in Canada hypothesized that the gut microbiome might contain enzymes that metabolize the blood antigens since these antigens are found on the gut wall. Through screening they found a bacterium that was able to metabolize blood group A to blood group O. This has the potential to alter the future blood supply.