There may be more genes in the human microbiome than the universe has stars, a new report finds.
In the first study of its kind, researchers from Harvard Medical School collected 3,500 microbiome samples from both the mouth and the gut.
One estimate put the number of genes at 232 million, while another was 'comparable to the number of atoms in the universe'.
Surprisingly, half of the genes researchers found seemed to be unique to an individual person.
The team says the findings could not only provide clues about environmental exposures or the risk of developing disease, but also lead to therapies that treat people based on their microbial genetic make-up rather than the type of bacteria they have.
A new study from Harvard Medical School has found there could be anywhere from 232 million genes in the human microbiome to as many as one million trillion, the number of stars in the universe (file image)
The human microbiome - the collection of bacteria that is in our noses, mouths, stomachs and elsewhere - is estimated to contain trillions of bacterial species.
The majority are harmless, some even helpful in enhancing immunity, fighting tumor growth, improving digestion and lowering cholesterol.
Others are harmful, causing plaque to form on the teeth as well as skin and soft tissue infections.
Most past studies have focused on identifying the different types of bacteria to learn how they affect our health.
'Ours is a gateway study, the first step on what will likely be a long journey toward understanding how differences in gene content drive microbial behavior and modify disease risk,' said study first author Braden Tierney, a graduate student at Harvard Medical School.
For the study, published in the journal Cell Host & Microbe, the team analyzed about 3,500 human microbiome