Thursday , March 30 2023

Bizar microbes represent a major branch on the evolutionary genealogy tree


Microscopic image a Hemimastix kukwesjijk, a new species of hemimastigoti.
Image: Yana Eglit / Dalhousie University

Canadian scientists have identified microscopic creatures that are so different from those previously observed, they had to create a whole new branch on the evolutionary tree of life to introduce them.

A new work published this week in Nature provides the first genetic analysis of hemimastigotes – a rare and poorly understood group of single-cell micro-organisms. Biologists know about these beasties for over a century, but only now, hemimastigotes can be officially introduced into the evolutionary tree of life, a more formal process known as phylogeny. And by doing so, scientists have come across a whole new branch on the tree of life – billions of years old.

Yana Eglit, a student at Dalhousie University and co-author of the new study, found two different hemimastigote species – one already known and one completely new for science – from soil samples collected along the Bluff Wilderness route in Nova Scotia, Canada . It's called the species known before Spironema and the new one was named Hemimastix kukwesjijk (pronounced "ku-ga-wes-jij-k"), which means "hairy kidnapper" in the language of the people of Miraculous First Nations in Nova Scotia.

Fast and hairy, really. These one-cell predators, in free roaming, have two rows of hair-like scars that they use to locate and catch prey. Hemimastix feeds through the connection of the mouth – if one can say that – at the surface of its prey as microscopic, withholding the cytoplasm of the victim, according to the observations made by Eglit and her colleagues.

A sampling of hemimagiasis analyzed in the new study.
Image: G. Lax et al., 2018 / Nature

Hemimastigotes can not be classified as animals, plants, fungi or bacteria. But they are eukaryotic, having complex cells and a clearly defined nucleus. Eukaryotes that can not be introduced into these conventional groups are called protists – a kind of cluster of non-classifiable eukaryotes. Such as hemimastigotes. In addition to their description as eukaryotes, scientists have failed to place them anywhere in the phylogenetic tree of life. Part of the problem was that scientists were unable to carry out significant genetic tests on hemimastigotes – but this has now changed due to the new research.

"This discovery literally turns our branch of the Tree of Life into one of the deepest points," said Alastair Simpson, lead author of the study and biology professor at Dalhousie, in a statement. "This opens a new door for understanding the evolution of complex cells – and their ancient origins – back before animals and plants appear on Earth."

Using a new technique called unique transcriponomy, and with the help of candidate Gordon Lax, the Dalhousie team managed to tease large amounts of genetic material from the two species of hemimastigoti. Whole genomes could not be extracted, but sufficient information was obtained for researchers to perform phylogenetic analysis.

Virtually all eukaryotes belong to either animal kingdoms, plants or fungi, but some eukaryotes can not be classified as such and are considered antistress. Not satisfied with these generic names, scientists created six "super-groups" for the eukaryotic domain: Sar / Telonemia, Haptophyta / Centrohelida, Archaeplastida / Picozoa (this group contains plants), Cryptista, Discoba and Amorphea animals and fungi).

To group these eukaryotes at the kingdom level, the scientists created an "over-group" called Diaphoretickes, which recorded four similar super-groups (see the diagram below). The purpose of this organizational scheme is to sort and group species according to their relationship with ordinary ancestors rather than their physical characteristics or other attributes.

The six super-groups of previously established eukaryotes and the supra-group Diaphoretickes plus the new over-group hemimastigotes proposed in the new study. Animals and mushrooms are in the super-group Amorphea, while the plants fall into Archaeplastida + Picozoa.

Earlier, scientists have designated Hemimastigophora at triage level (under the kingdom), but the new study suggests they belong to a distinct supra-group or a "Roman line of over-re-eukaryotic regrowth," in the words of the researchers.

"From our analysis it was clear that hemimastigotes did not belong to any group known at the level of directing or even a known" super-group " of several kingdoms together, such as that which includes both animals and mushrooms, "Simpson said." This small collection of organisms is a whole new group at that level, all on its own. It is a branch of the Tree of Life that has been separated for a very long time, maybe more than a billion years, and we have no information about it. "

Graphics: Peter Halasz

Besides being the first to perform a genetic analysis of hemimages, the Dalhousie team is also the first to cultivate these organisms. Armed with a constant amount of hemimastigoti to experiment, researchers now hope to collect more genetic information from these remarkable creatures.

Andreas Hejnol, leader of the International Center for Marine Marine Biology Center at the University of Bergen, said the work is valuable in providing a phylogenetic analysis that ultimately brings these organisms to the tree of life.

"Methods are standard, and the major achievement is finding organisms in sufficient quantities to isolate molecules and get information about sequences," Hejnol, who was not affiliated with the new study, told Gizmodo. "Another great breakthrough is that researchers are actually able to cultivate them."

Praising it aside, Hejnol said that it is important to remember that certain categories such as the super-kingdom and the super-group are simply "anthropic categories" that scientists use to classify and organize organisms – as our understanding of biology changes.

"The criteria are not well defined and are based mainly on the" distinctive character "of other organisms," he said. "This distinction is largely based on randomly chosen criteria. Before that, evolutionary biologists normally use similarity as a criterion to designate organisms together."

In the new study, the phylogenetic analysis placed hemimastigotes on a new major branch – one that is now alongside a branch of preexisting eukaryotes, known as diaphoretic.

"Although this position is interesting and useful for reconstructing the evolution of these organisms, the exclusion of hemimastigotes is arbitrary," Hejnol told Gizmodo. "They [hemimastigotes] could be included [in the Diaphoretickes group]- this is in the eyes of the viewer. This again shows how arbitrary assignments are, such as the "super-kingdom." "

He adds: "The" super-king "novel sounds fanciful and interesting – but it has no scientific value. It is a pity that it hides the authors' main achievement that they can put this group into the tree of life – which is truly scientific progress. "

Going forward, it will be interesting to see if other scientists agree with this classification. As mentioned, there are other species of hemimastigoti; perhaps a further phylogenetic research will confirm the creation of this new group over-group or could inflame this debate even further. Otherwise, this discovery shows the need for improvement ways of describing and classifying organisms along the highest branches of the tree of life.

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