Although each city had its own unique microbial profile, there was a “core urban microbiome” that all of the cities shared, they found. The scientists, members of the international MetaSUB consortium, also discovered more than 10,000 previously unidentified species of viruses and bacteria. They published the findings in the journal Cell on Wednesday. “We have taken a deep dive into the urban centers to find a breadth and treasure trove of new life-forms,” Dr. Mason said. “The railings and the benches of our cities have sometimes just as much or more diversity than what you find in a rain forest.” The source and function of many of these microbes remains unknown, and the research reveals how much is left to learn about the microorganisms that surround us. But the findings should not be cause for alarm, the scientists stress.