Ten previously undescribed strains of microbial predators isolated from geographically distinct marine habitats — including coral reefs of Curaçao, nearshore sediments of the Black Sea and the Red Sea, and the water columns of the North-East Pacific and Arctic oceans — collectively form a diverse new supergroup of eukaryotes, termed Provora.
Living cells, visualized by light microscopy, showing the nibblerid microbial predator Ubysseya fretuma. Image credit: Tikhonenkov et al., doi: 10.1038/s41586-022-05511-5.
“Like lions, cheetahs, and more familiar predators, these microbes are numerically rare but important to the ecosystem,” said University of British Columbia’s Professor Patrick Keeling.
“Imagine if you were an alien and sampled the Serengeti: you would get a lot of plants and maybe a gazelle, but no lions. But lions do matter, even if they are rare. These are lions of the microbial world.”
Professor Keeling and colleagues isolated the unusual microbial predators from water samples collected from coral reefs of Curaçao, nearshore sediments of the Black Sea and the Red Sea, and the water columns of the North-East Pacific and Arctic oceans.
“I noticed that in some water samples there were tiny organisms with two flagella, or tails, that convulsively spun in place or swam very quickly. Thus began my hunt for these microbes,” said Institute for Biology of Inland Waters Dr. Denis Tikhonenkov.
The researchers noticed that in samples where these microbes were present, almost all others disappeared after one to two days.
They fed the voracious predators with pre-grown peaceful protozoa, cultivating the organisms in order to study their DNA.
“In the taxonomy of living organisms, we often use the gene ‘18S rRNA’ to describe genetic difference. For example, humans differ from guinea pigs in this gene by only six nucleotides,” Dr. Tikhonenkov said.
“We were surprised to find that these predatory microbes differ by 170 to 180 nucleotides in the 18S rRNA gene from every other living thing on Earth. It became clear that we had discovered something completely new and amazing.”
On the tree of life, the animal kingdom would be a twig growing from one of the boughs called domains, the highest category of life.
But sitting under domains, and above kingdoms, are branches of creatures that biologists have taken to calling supergroups.
The Provora supergroup is genetically, morphologically and behaviorally distinct from other eukaryotes, and comprises two divergent groups: Nebulidia and Nibbleridia.
These groups are superficially similar to each other, but differ fundamentally in ultrastructure, behavior and gene content.
“This is an ancient branch of the tree of life that is roughly as diverse as the animal and fungi kingdoms combined, and no one knew it was there,” Dr. Keeling said.
The team’s paper was published in the journal Nature.
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D.V. Tikhonenkov et al. Microbial predators form a new supergroup of eukaryotes. Nature, published online December 7, 2022; doi: 10.1038/s41586-022-05511-5
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