The largest bacterium in the world was discovered in Guadeloupe

published on Thursday, June 23, 2022 at 8:37 p.m.

It can be caught using tongs: the world’s largest bacterium, 5,000 times larger than its peers and with a more complex structure, was discovered in Guadeloupe, according to a study published Thursday in the journal Science.

“Thiomargarita magnifica” measures up to two centimeters, looks like “silver” and shakes microbiology codes, described by AFP Olivier Gros, professor of biology at the University of the West Indies, co-author of the study.

In his laboratory on the Fouillol campus, in Pointe-à-Pitre, the researcher proudly displays a test tube with tiny white filaments. If the average size of a bacterium is two to five micrometers, it’s “visible to the eye, I can do it with tweezers!”, He wonders.

It was in the mangroves of Guadeloupe that the researcher observed the germ for the first time, in 2009. “At first I thought it was just a bacterium because something two centimeters cannot be one”.

Quite simply, cellular imaging techniques with an electronic microscope show that it is a bacterial organism.

But at this size, says Professor Gros, “we’re not sure it’s a cell” – a bacterium that is a unicellular microorganism.

A biologist from the same laboratory revealed that it belongs to the Thiomargarita family, a well -known bacterial genus that uses sulphides to thrive.

And work done in Paris by a CNRS researcher suggests that we are dealing with “one and the same cell”, Professor Gros explains.

– “As big as Mount Everest” –

Convinced of their findings, the team attempted a first publication in a scientific journal, which failed. “We were told: it was interesting but we lacked the information to believe you”, the evidence was not strong enough in image terms, the biologist recalled.

Enter Jean-Marie Volland, a young post-doctoral student from the University of the West Indies, who will be the first author of the study to be published in Science.

Unable to secure a teaching-researcher position in Guadeloupe, the 30-year-old flew to the United States, where he was recruited by the University of Berkeley. Getting there, he decided to study the “incredible bacteria” he was already familiar with.

“It’s like meeting someone as tall as Mount Everest,” he thought to himself. In the fall of 2018, he received a first package sent by Professor Gros to the genome sequencing institute’s Lawrence Berkeley national laboratory, which is run by the university.

The challenge is very technical: to successfully interpret a picture of the bacterium as a whole, thanks to “three-dimensional microscopy analysis, at higher magnification”.

In the American laboratory, the researcher has advanced techniques. Not forgetting the important financial support and “access to expert genome sequencing researchers”, recognized the scientist, who qualified this American-Guadeloupian collaboration as a “success story”.

The 3D images finally make it possible to prove that the entire filament is a single cell.

In addition to its “gigantism”, the bacterium has also become “more complex” than its peers: an “unexpected” discovery, which “shakes a lot of knowledge in microbiology”, the researcher confirms.

“While common in bacteria, DNA floats freely in the cell, in it it is assembled into small structures called pips, a type of small bags surrounded by a membrane, that separates DNA from the rest. in the cell ”, development by Jean- Marie Volland.

This compartmentalization of DNA – the molecule that carries genetic information – “is a characteristic of human, animal, plant cells … not of all bacteria”.

Future research should tell if these traits are specific to Thiomargarita magnifica or if they can be found in other bacterial species, according to Olivier Gros.

“This giant bacterium questions many established rules of microbiology” and “offers us an opportunity to observe and understand how complex a living bacterium is”, enthusiastically Jean-Marie Volland.

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