The humble dust collecting in the average American household harbors a teeming menagerie of bacteria and fungi, and as researchers from the University of Colorado Boulder and North Carolina State University have discovered, it may be able to predict not only the geographic region of a given home, but the gender ratio of the occupants and the presence of a pet as well. The new findings, which were published today in the journal Proceedings of the Royal Society B, highlight the impressive amount of microbial diversity in the average household and the degree to which these organisms can tell a story about the homes they inhabit.

"Every day, we're surrounded by a vast array of organisms in our homes, most of which we can't see," said Noah Fierer, an Associate Professor in the Department of Ecology and Evolutionary Biology at CU-Boulder and a co-author of the study. "We live in a microbial zoo, and this study was an attempt to catalog that diversity."

The study examined roughly 1,200 homes across the continental U.S. Volunteers participating in the Wild Life of Our Homes citizen science project helped researchers collect indoor and outdoor dust samples at each site.

On average, each home contains more than 5,000 different species of bacteria and around 2,000 species of fungi. Fungal communities tend to be more predictive of a home's location while bacterial communities provide clues about the identity of its residents.

"Geography is the best predictor of fungi in your home," said Fierer, who is also a research fellow at the Cooperative Institute for Research in Environmental Sciences (CIRES) at CU-Boulder. "The reason is that most fungi blow in from outdoors via soil and leaves," he said, noting that a home in the upper Midwest, for instance, will harbor distinct fungi compared to a home in the Southeast.