For decades, the bacteria group Candidate Phylum TM7, thought to cause inflammatory mucosal diseases, has posed a particular challenge for researchers. A landmark discovery has revealed insights into TM7's resistance to scientific study and to its role in the progression of periodontitis and other diseases. These findings shed new light on the biological, ecological and medical importance of TM7, and could lead to better understanding of other elusive bacteria.

Source: How 'microbial dark matter' might cause disease