This happens to be one of the grossest things I have come across lately; and it is no joke. There are a group of researchers who are interested in belly button bacteria. Their project is called Belly Button Biodiversity with researchers from North Carolina State University and the North Carolina Museum of Natural Sciences all studying the matter at hand.
Their goal is to "introduce humans to the wildlife that's growing on us and in us." If this interests you and you would like to see what your belly button bacteria looks like, the next sampling event is on February 12, at the North Carolina Museum of Natural Sciences.