We know from previous work that people with a lactase-non-persistent (LNP) genotype have more Bifidobacteria in their guts, but what kinds? Victor Schmidt and fellow post doc Hagay Enav dive into this question using samples from TwinsUK. They use genome-capture to enrich for Bifido DNA in particular, and Hagay developed a new synteny-based strain comparison tool. They find that all Bifidos are enriched in the LNP, not any kind in particular. And Bifidos are loyal! They stick to their hosts over time.