A team of researchers led by the European Molecular Biology Laboratory's Peer Bork reports that there are three human gut microbiome enterotypes in Nature this week. Using 22 newly sequenced fecal metagenomes from people from four countries as well as previously published data, the researchers identified three clusters that people's gut microbiomes fall into and found that those clusters are not specific to nations or continents. The enterotypes do differ in composition and enzyme production — enterotype 1, which is marked by high levels of Bacteroides, produces more vitamin B7 enzymes, while Enterotype 2, which has many bacteria from the genus Prevotella, makes more thiamine enzymes, writes Carl Zimmer in The New York Times. "It's an important advance," the University of Colorado's Rob Knight, who was not involved in the research, told the Times. "It's the first indication that human gut ecosystems may fall into distinct types," Knight added. Bork told the Times that as more research and more samples are needed for further investigations into these enterotypes, his group has expanded its study to include 400 people.