Researchers from the University of British Columbia have identified enzymes from gut bacteria that have the ability to change donated blood to Type O. As shown in this SciShow video, they used metagenomic sequencing to identify the genes that cleave away A and B antigens, and then inserted those genes into E. Coli. The resulting bacteria are easy to produce and the their enzymes are reportedly 30x more efficient  at cleaving A and B antigens than earlier methods.