Your gut microbiome can convert A and B blood types into the universal type O.

Source
CC0 Creative Commons

Another fascinating thing our gut bacteria do...

Within the ABO blood group system, you are either type A, B, AB or O depending on the nature of the antigen present on your red blood cells.

Recently at the National Meeting & Exposition of the American Chemical Society (1) researches presented work that show they have identified enzymes from the human gut microbiome that can convert type A or B blood into type O. The enzymes recognize and cleave the A and B antigens on red blood cells (simple sugars).

The researchers hope that one day these enzymes could be used to convert type A or B blood into universal donor Type O blood in emergency situations. Type O blood donors are universal donors because their blood does not have the A or B antigens and when given to a recipient it will not be seen as a foreign antigen and therefore not cause a immune response.

The research was done at the University of British Columbia Canada, headed by professor Stephen Withers.

Sources:
(1 )Withers S et al. Discovery of CAZYmes for cell surface glycan removal through metagenomics: towards universal blood. Presented at: the 256th National Meeting & Exposition of the American Chemical Society, Boston, MA, USA, 19–23
Link to the abstract

You can watch a YouTube video of the research here: