Research looking at bacteria that live on or in us and are unculturable, that may be behind some diseases, and that some researchers call "microbial dark matter". From Red Orbit - Your Universe Online:
Scientists from University of California Los Angeles (UCLA), J. Craig Venter Institute and the University of Washington have achieved a major breakthrough in the understanding of what they call “microbial dark matter.” These are the countless bacteria which inhabit our bodies and about which so little is known.
Amazingly, there are 10 times more bacterial cells in the body than other cells. But approximately half of those bacteria are almost impossible to replicate for scientific research. This has restricted our ability to understand their role in human biology and disease. This led to the term “microbial dark matter.” For a long time, biologists have thought that these “uncultivable bacteria” may be involved in the development of some serious and chronic diseases.
One particular bacteria group, Candidate Phylum TM7, has been an especially difficult challenge for researchers. Because it is so prevalent in people with periodontitis, an infection of the gums, TM7 has been implicated in causing inflammatory mucosal diseases. Decades of research into this connection proved fruitless. But now, in a major breakthrough, scientists at the UCLA School of Dentistry, the J. Craig Venter Institute and the University of Washington School of Dentistry believe they have cracked the problem.
From the American Microbiome Institute regarding the same research: