‘Dark matter’ microbes add 20 new branches to the tree of life

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By Alice Klein

They were right under our noses all along – thousands of novel microscopic life forms, now unmasked by genetic analysis. Many belong to entirely new groups, as different from other microbes as an insect is from a chimpanzee.

Earth’s microorganisms are split into groups called bacteria and archaea. Together, they make up the vast majority of species on the planet, but until recently we were only able to study a tiny fraction of them.

This is because less than 10 per cent can be isolated and grown in the lab. The rest can only survive in the conditions of their native environment – be it a hydrothermal vent or the guts of a cow. Researchers call them microbial dark matter.

However, a technique called metagenomics is bringing them to light. It involves taking an environmental sample, sequencing all the DNA in it – its metagenome – then piecing together the genomes of each of the microbes present. “It’s like getting a mix-up of lots of different jigsaw puzzles, and then trying to put together the pieces of each individual puzzle,” says Donovan Parks at the University of Queensland in Australia.

Parks and his colleagues analysed more than 1500 metagenomes that researchers worldwide had uploaded to a public database. Each contained jumbles of DNA sequences collected from environments such as soil, the ocean, hydrothermal vents, industrial effluent, and cow and baboon faeces.

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