The tree of life has undergone a dramatic makeover due to the addition of over 1,000 new species discovered in recent years.
The added species, mostly bacteria and single-celled microorganisms known as Archaea, show that much of the life that we see around us represents just a tiny percentage of the world's biodiversity.
"The tree of life is one of the most important organizing principles in biology," Jill Banfield of the University of California at Berkeley said in a press release. "The new depiction will be of use not only to biologists who study microbial ecology, but also biochemists searching for novel genes and researchers studying evolution and earth history."
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The new tree of life and related findings are published in the latest issue of the journal Nature Microbiology.
Charles Darwin first sketched a tree of life in 1837 as he sought ways of showing how plants, animals and bacteria are related to one another. The tips of the twigs on such images represent life on Earth today, while the branches connecting them to the trunk indicate evolutionary relationships.
A branch that divides into two twigs near the tips of the tree shows that these organisms have a recent common ancestor, while a forking branch close to the trunk implies an evolutionary split in the distant past.
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But Darwin knew nothing of the newly added microorganisms, which before their discoveries over the past 15 years were lurking unseen in Earth's nooks and crannies. It was only after the genome revolution that technical advances permitted Banfield and others to search for other life forms directly in the field, as opposed to trying to culture them in a lab dish.
It would be to find some of the new organisms in a lab dish anyway, since many microbes cannot be isolated and cultured. That is because they cannot live on their own. They must beg, borrow or steal from other animals or microbes, either as parasites, symbiotic organisms or scavengers.
"Bacteria and Archaea from major lineages completely lacking isolated representatives comprise the majority of life's diversity," said Banfield, who also works at the Lawrence Berkeley National Laboratory. "This is the first three-domain genome-based tree to incorporate these uncultivable organisms, and it reveals the vast scope of as yet little-known lineages."
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The additions to the revised tree of life, only known from their genomes, come from a variety of environments. They include the human gut, dirt under toxic waste sites, a hot spring in Yellowstone National Park, toxic puddles in abandoned mines, a salt flat in Chile's Atacama desert, terrestrial and wetland sediments, a sparkling water geyser, meadow soil and the inside of a dolphin's mouth.
A new star player on the tree of life is a group of bacteria described as the "candidate phyla radiation," which forms a very major branch. This group is now believed to contain around half of all bacterial evolutionary diversity.
Co-author Brett Baker said, "This incredible diversity means that there are a mind-boggling number of organisms that we are just beginning to explore the inner workings of that could change our understanding of biology."