The Human Microbiome Project has catalogued the genetic identity of many bacteria, viruses and other organisms that live in intimate contact with us.
They are not germs that need eliminating but a fundamental part of what makes us human, researchers say.
Yet until recently, little was known about the identity of trillions of the microbes populating our bodies.
For centuries we could only investigate microbes that can survive in laboratories and study them in isolation – often one microbe at a time.
But with the advent of ever-improving techniques to sequence DNA, the Human Microbiome Project has been able to uncover microbes that have never been seen before and look at how they behave as communities.
Many of the results of the five-year project, launched by the National Institutes of Health, have been published in Nature and PLoS journals.
Over 200 healthy men and women from the US had microbe samples taken from various parts of their bodies.
And researchers were able to find over 10,000 different types of organisms as part of the healthy human microbiome.
Most of these microbes appeared to do no harm at all. In fact, there is growing evidence that these bugs help us in many ways.
Dr Lita Proctor, programme director of the project says there is a growing understanding that we pick it up in the very early stages of life.
“The human genome is inherited but the human microbiome is acquired- that means it has a very important changeable, mutable property.
“This gives us something to work with in the clinic. If you can manipulate the microbiome you can keep a healthy microbiome healthy or re-balance an unhealthy one,” she says.
But who owns the microbiomes inhabiting our bodies? And what does this mean for the regulation of pro-biotics that can change them?, asks ethicist Prof Any McGuire of Baylor College of Medicine.
These are questions that will need to be ironed out as our knowledge of this area expands, she says.
But we only have half the story. We need to find out much more about how the microbiome talks to human cells says Prof David Relman of Stanford University.
“It is still an unknown land. Even though it is on home turf we are still discovering new life forms on it,” he says.