Rare microbial predators with voracious appetite form a new branch in ‘tree of life’: Study

Scientists have uncovered a new branch on the tree of life or the graphical tool that shows the evolutionary relationships among plants, animals and all other life forms.

A rare group of microbial predators dubbed the “lions of the microbial world” make up this new branch on the tree of life, a new research has said. The tree is classified into three domains — eukaryotes (organisms whose cells contain a nucleus), bacteria and archaea (single-celled microbes living in extreme conditions).

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These microbial predators form a new branch in the tree of eukaryotes, stated the study published in Nature journal December 7, 2022.

These organisms swallow their prey whole or munch them in chunks. They were discovered 10 years ago in a wide range of marine habitats.

These include the coral reefs of Curaçao (an island country in the Dutch Caribbean), nearshore sediments of the Black and Red Seas and the water columns of the northeast Pacific and Arctic Oceans.

The researchers realised that these organisms were connected after they kept finding them year after year.

“We call them a new group because, in the tree of eukaryotes that are not closely related to any other major group, they make their branch,” Patrick Keeling, professor at the University of British Columbia, told Down To Earth.

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In the tree of eukaryotes, these organisms form a new branch or supergroup — Provora. Supergroups include organisms evolving from a single common ancestor.

“At the level of DNA sequences, they are about as diverse as all animals and all fungi put together,” he added.

The researchers cultivated these organisms in the lab. Denis Tikhonenkov from the Russian Academy of Sciences and one of the co-authors fed these predators with other microorganisms.  

The team noticed something odd: The prey disappeared in one-two days. 

They feed on other microbial eukaryotes, such as protozoa. Based on their feeding behaviour, this supergroup is classified into nibblerids and nebulids.

The former engulfs the prey, while the latter comes equipped with tooth-like protrusions to help them bite and ingest parts of their prey. Nebulids can also swallow their prey, but they prefer nibbling instead.

This feeding mode is unique, the study read. It shows how flagellates can feed on larger cells, which is often not considered in the modelling of microbial food webs, it added.

Flagellates are organisms that use flagella — hair-like appendages — to move around. These predators are tiny and fast-swimming, the scientists noted.

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The researchers then sequenced a particular gene called the 18S ribosomal RNA, which can help identify organisms and study their genetic differences. 

These predatory microbes differ by 170-180 nucleotides (the basic building block of nucleic acids) in the 18S rRNA gene from every other living organism on the Earth,Tikhonenkov explained.

The study highlighted that these organisms are ancient life forms due to shared characteristics with distant relatives.

The researchers argued that learning more about these undiscovered branches of life can help shed more light on the foundations of the living world and how evolution works.

The new findings “emphasise how little we still know about the actual biodiversity of Earth. That a widespread and diverse group like this can still be completely unknown means we have more exploring to do,” Keeling said.

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