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Does YOUR gut contain an entirely new form of life? Scientists say mystery 'fourth domain' may be lurking inside us all

Scientists studied 86 unusual gene families to track unknown sequences
Some found to share 60 percent or less DNA with known sequences
Study suggests presence of 'fourth domain,' new group of life forms

Published: 13:36 EST, 13 November 2015 | Updated: 13:44 EST, 13 November 2015

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The dark matter of life may be lurking in your gut.

A new method of identifying unusual genes has led scientists at Marie Curie University in Paris and the University of Montreal in Canada to believe that some unseen microbes may exist within a new classification, a fourth domain of life.

Scientists Philippe Lopez and Eric Bapteste developed the solution, working alongside Sebastian Halary to focus on 86 gene families which are rarely swapped between different microbes.

What they found was more variability in the genes than previously thought to exist.

Microbes have the ability to swap genes, making it difficult for scientists to distinguish between different groups. When gene sequences are identified from a DNA analysis, they often cannot be interpreted

THE DARK MATTER OF LIFE

Scientists from Marie Curie University in Paris and the University of Montreal in Canada sampled DNA from 86 unusual gene families in the human gut.

Further analysis traced found that some sequences in these families shared 60 percent or less DNA with any known gene sequences.

This suggests, but does not conclude, that there may be a new domain of life.

Current classifications account for three groups of life: eukaryotes, bacteria, and archaea.

These mysterious microbes may fall outside of these categories and into a fourth domain.

'It's as if they belonged to unknown lineages of microbes that diverged very early in the history of life,' Lopez told New Scientist.

Current classifications split life into three major domains.

Eukaryotes—plants, animals, and fungi—are defined by their nucleus, and less complex cells are divided between bacteria and archaea.

Microbes have the ability to swap genes, making it difficult for scientists to distinguish between different groups.

When gene sequences are identified from a DNA analysis, they often cannot be interpreted.

With scientists still unable to grow 99 percent of microbes in a lab, some have begun to suspect that there are new forms of that have yet to be discovered.

The human gut microbiome, the environment in which microbial communities interact inside of the gut, is the best studied of all such communities.

Still, the full scope of the microbes harbored within the gut is mystery.

In their research, the team collected more than 200,000 DNA samples relating to the sequences in the 86 unusual gene families.

Using these sequences for deeper analysis, the scientists found 80,000 more stretches of DNA within the same families.

The analysis found that one-third of this DNA shared 60 percent or less of its identity with any known gene sequences, a difference that can separate different domains of life.

'Let's wait to see how unusual the organisms are,' says Bapteste to New Scientist.

'Scientists have found a huge diversity of microbes in the human gut, so I would not expect it to be necessarily hostile to different life forms,' he says.

'The good news is we now know something about them that could help us to fish them out,' he says.

The evidence is suggestive of a fourth domain, but scientists urge caution before making a conclusive classification.

Researchers have been sampling DNA from this area for 25 years without capturing the new lifeforms.

'The discovery of archaea revolutionized our fundamental knowledge in biology,' says Bapteste. 'These deep lineages, if they exist, still need to be captured.'