Bacteria are all over us, inside and out. Jiri Hulcr recently found 1,458 species of bacteria "new to science" in a small sample of human belly buttons. What we know about our little passengers and how they affect our bodies is dwarfed by what we do not. That can be disconcerting to think about, especially when some of them are undermining us.
In particular, some bacteria in our own intestines seem to have turned against us. Research this week in the New England Journal of Medicine led by Dr. Stanley Hazen at the Cleveland Clinic tells how they digest a compound called choline and turn it into trimethylamine N-oxide (TMAO).