Have biologists specializing in the microscopic world missed an entire branch of the tree of life? This is suggested by a study published by a Russian-Canadian team in the journal Nature (8/12/2022).
The authors describe two new, hitherto unknown species of microbes, “nibbleridae”.to bitemeaning ‘nibbling’, which feed by nibbling off pieces of their prey using tooth-like structures or swallowing them whole) and ‘nebulids’.
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According to their work, these organisms form a separate “supergroup” among eukaryotes (the domain of life that includes plants, fungi and animals).Provora“.
Predators are rare in number but important to the ecosystem
Lead study author Patrick Kieling, a professor in the department of botany at the University of British Columbia (UBC) in Canada, says that like lions, cheetahs and other predators visible to the naked eye, these microbes are rare in number but important to the ecosystem. in a press release.
“Imagine you are an alien sampling the Serengeti (One of Tanzania’s most famous national parks, editor’s note) : you will get lots of plants and maybe gazelles, but no lions. Again, lions are important, albeit rare“, the researcher shows that Provora “lions of the microbial world“.
The team discovered these “microbial lions” by analyzing water samples taken from marine habitats around the world, including the coral reefs of Curaçao (an island in the Dutch Caribbean), the Black Sea and the Red Sea, as well as water samples. Northeast Pacific and Arctic oceans.
Cultivating “germ lions” to study their DNA
“I noticed that some of the water samples had tiny organisms with two flagella or tails that spun around in place or swam very quickly. So I began the hunt for these microbes“, the first editor of the study, scientific worker of the Russian Academy of Sciences, Dr. Denis Tikhonenkov, quotes in the press release.
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The Russian scientist noted that in samples containing these microbes, almost all other organisms disappeared after a day or two. In fact, they were just eaten.
The researcher therefore experimented with feeding protozoa – already known single-celled organisms – to isolate the prey and culture them in order to extract and study their DNA. They point to a complex process slowed by both the war in Ukraine and Covid, which has prevented Russian scientists from visiting their Canadian counterparts.
“In taxonomy (classification science) living things, we often use the ’18S rRNA’ gene to describe the genetic difference between organisms. For example, humans differ from guinea pigs in this gene by only six nucleotides. (building blocks of genetic sequence),” says Dr. Tikhonenkov.According to this criterion, we were surprised to see that predatory microbes differ from all living things on earth by 170-180 nucleotides. It turns out that we have discovered something completely new and amazing.”
The next step: complete sequencing of their genome
In classifying organisms according to their relationships, “supergroups” form an intermediate level between a domain—eukaryotes, prokaryotes, and archaea—and a kingdom (such as animal, plant, or fungus). Between five and seven eukaryotic supergroups have been discovered so far, the most recent of which was in 2018.
However, a better understanding of these potentially unknown branches is crucial to understanding the fundamentals of the living world and evolutionary mechanisms, the authors emphasize. “Ignoring microbial ecosystems is like having a house to renovate and just redecorating the kitchen, as we often do, but ignoring the roof or foundation.“, Dr. Keeling describes.
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The next step for the team’s scientists: fully sequence the genomes of the “germ lions” and model the cells in 3D to learn more about their molecular structure, structure and feeding habits.
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