Visible to the naked eye, the world’s largest bacteria discovered in Guadeloupe

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

Magnificent Thiomargarite“it measures up to two centimeters, it looks like a”cylinder“and shakes the codes of microbiology”, describes Olivier Gros, professor of biology at the University of the West Indies, co-author of the study, to AFP.

In his laboratory on the Fouillol campus in Pointe-à-Pitre, the researcher proudly displays a test tube containing small white filaments. When the average size of a bacterium is two to five micrometers, “can be seen with the naked eye, I can take it with tweezers!“, he marvels.

two centimeters

It was in the Guadalupe mangrove where the researcher observed the microbe for the first time, in 2009.”At first I thought it was anything but bacteria because something two centimeters can’t be.“.

Quickly, cell description techniques with electron microscopy show that, however, it is a bacterial organism.

But at this size, says Professor Gros, “we were not sure that it was a single cell“- a bacterium that is a single-celled microorganism.

A biologist from the same laboratory reveals that it belongs to the Thiomargarita family, a well-known bacterial genus that uses sulfides to develop.

And a study carried out in Paris by a CNRS researcher suggests that we are facing “one and the same cell“, explains Professor Gros.

As high as Mount Everest

Convinced of their discovery, the team attempts a first publication in a scientific journal, which fails. “They told us: it is interesting but we lack information to believe you“, the test not being robust enough in terms of image, recalls the biologist.

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

Not having obtained a teaching-research position in Guadeloupe, the 30-year-old flew to the United States, where he was recruited by the University of Berkeley. Going there, he had in mind to study”the incredible bacterium“with which I was already familiar.

It would be like meeting a human as tall as Mount Everest.

It would be like meeting a human as tall as Mount Everesthe said to himself. In the fall of 2018, he received a first package sent by Professor Gros to the Genome Sequencing Institute at the Lawrence Berkeley National Laboratory, run by the university.

The challenge was fundamentally technical: managing to generate an image of the bacterium as a whole, thanks to “higher magnification three-dimensional microscopy analysis“.

In the American laboratory, the researcher had advanced techniques. Without forgetting an important economic support and “access to expert researchers in genome sequencing“, acknowledges the scientist, qualifying this American-Guadeloupean collaboration as “success story“.

Their 3D images finally make it possible to prove that the entire filament is, in fact, a single cell.

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