A Revised Tree of Life

Author:  Julie Spitzer

Institution:  University of Wisconsin-Madison


A team of scientists, led by Jillian Banfield of the University of California - Berkeley, redesigned the Tree of Life on Monday after discovering thousands of new bacterial organisms over the last 15 years, according to a UC-Berkeley news release.

Charles Darwin first sketched out his idea of the lineage of all species in 1859. He compared evolution to a tree. Ever since, biologists have recreated this metaphor. Adding new species has always presented a challenge because many single celled organisms, or microbes, were hard to grow and subsequently study in labs. Gene sequencing techniques made this easier.

Older trees emphasized evolutionary relationships, particularly the eukaryote diversity of life. However, they neglect many bacteria obtained from unexamined environments and understood through genomic sampling. Banfield and her team gathered genome sequences from such environments to identify the organisms. This revealed over 1,000 uncultivated organisms the older trees lacked, creating a larger and revised tree, according to the study published in Nature Microbiology.

“This tree highlights major lineages currently underrepresented in biogeochemical models and identifies radiations that are probably important for future evolutionary analyses,” the study’s authors said.

Microbes are difficult to work with because they cannot be created in a lab. They thrive off their environments or other animals near them. This is why the genome revolution is so important to their study. In fact, all of the newly recognized organisms are only known for their genomes, according to the UC-Berkeley news release.

“What became really apparent on the tree is that so much of the diversity is coming from lineages for which we really only have genome sequences,” Banfield said in the UC-Berkeley news release. “We don’t have laboratory access to them, we have only their blueprints and their metabolic potential from their genome sequences. This is telling, in terms of how we think about the diversity of life on Earth, and what we think we know about microbiology.”

With all the new bacteria added onto the tree, there are still some similarities to the old ones. For example, Eukaryotes and Archaea still maintain close relations. However, there’s another remarkable addition. It is called the “candidate phyla radiation”. This branch was previously recognized to contain all symbiotic bacteria. It now, however, contains half of all bacterial evolutionary diversity.  

“The candidate phyla radiation has as much diversity within it as the rest of the bacteria combined,” she said in the release.

Banfield believes more eukaryotic branches, particularly microscopic fungi, may still remain undiscovered, she told the New York Times. However, there is still likely many more bacteria to find, said other authors of the study.

The world of bacteria is large and diverse and now fits inside our tree of life. Adding new species to the tree will always be a difficult task, but the genome revolution provides a technique to study the organisms that pose a challenge. With many new species added, life’s branches may spread that much wider.