The genetic secrets of some of the most abundant and diverse forms of life on Earth have been uncovered by scientists.
Researchers have sequenced the genomes of 201 microbes to find out more about the role these tiny, single-celled organisms play in our environment.
This insight into the genetic code has also helped the team to draw up a more detailed version of the microbial family tree.
The work is published in Nature.
Phil Hugenholtz, director of the Australian Centre for Ecogenomics at the University of Queensland, in Australia, said: "For almost 20 years now we have been astonished by how little there is known about massive regions of the tree of life. This project is the first systematic effort to address this enormous knowledge gap.
"For me, taxonomic assignment is important as it welcomes in strangers and makes them part of the family. Yet this is just a start. We are talking about probably millions of microbial species that remain to be described."
Microbes are found almost everywhere. They can thrive in the most hostile places on Earth, and are found in the polar ice, the deepest depths of the ocean and the driest parts of the deserts.
Scientists estimate that there are many millions of species.
But, unfortunately for scientists, the one places where these tiny organisms fail to do well is the laboratory. The vast majority of microbes are difficult to grow, which makes studying them difficult.
Now, though, scientists have taken advantage of new genetic technology that allows a genome to be sequenced from a single cell.
Using this, an international team has been able to reveal the genetic code of 201 different microbes, without the need to cultivate them in the lab.
These include species that live deep underground in a mine in South Dakota, in the Great Boiling Spring of Nevada as well as in the middle of the ocean.
Their DNA has shown that some of the organisms are so different from any seen before that 29 new branches need to be drawn on the microbial tree of life.
The genomes will also help scientists to study the biological features that allow microbes to survive in places where all other life fails.
Tanja Woyke, from the US Department of Energy Joint Genome Institute, said: "What we are now discovering are unexpected metabolic features that extend our understanding of biology and challenge established boundaries between the domains of life."