The human body contains roughly 10 trillion human cells . . . and harbors 100 trillion microbes - naturally-occurring bacteria that can be helpful, even essential to our health. Taken together, all these microscopic residents comprise what’s called the human microbiome. To expand our knowledge of this complex symbiosis, a new “citizen science” project has reached out for public funding . . . and microbial samples, too, from thousands of people, from all walks of life, from around the world. From Boulder Colorado, Shelley Schlender reports about the American Gut Project.