The discovery of the largest bacteria in the world .. can be caught with eyebrow tweezers

The largest bacteria in the world was discovered in the French islands of Guadeloupe, according to a study published in the journal "Science", which showed that it is five thousand times larger and has a more complex composition than other types of bacteria, and can be caught with eyebrow tweezers.

The bacterium, called Thiomargarita magnifica, measures up to two centimeters and looks like an "eyelash", and it has turned upside down what was so far known in microbiology, according to Olivier Gros, professor of biology at the University of the Antilles, who co-authored the study.

In the university's laboratory in Foyol, Pointe-a-Pitre, the researcher proudly displays a test tube containing tiny white threads.

He says that "seeing this germ is possible with the naked eye", as well as "holding it with tweezers!", while the average size of bacteria usually ranges between two and five micrometers.

The first time that the researcher observed the presence of the microbe in Guadeloupe was in 2009. He says that he did not think "at first that it was a bacteria because something two centimeters in size could not be."

However, cellular characterization techniques by electron microscopy soon revealed that it was indeed a bacterial organism.

However, its size prevented us from making sure that “it was a single cell”, as Professor Groh explains, since bacteria are defined as a single-celled microorganism.

And a biologist from the same laboratory concluded that the bacterium belongs to the family Thiomargarita, a well-known bacteria that uses sulfides to grow.

Professor Groh explains that studies conducted by a researcher at the National Center for Scientific Research in Paris showed that it is from a "single cell".

After the team was convinced of what it had discovered, it sought to publish the results of its research for the first time in a scientific journal, but the attempt did not bear fruit.

“We were told that our finding was interesting but that they lacked information to make them believe us,” says the biologist, and that the evidence is not strong enough in terms of image.

Then, Jean-Marie Volan, a young post-doctoral researcher from the University of the Antilles, who later became the first author of the study published in the journal "Science", entered the line.

Not having a professor-research position in Guadeloupe, the 30-year-old traveled to the United States, where he was hired by the University of Berkeley.

Folan was planning to take advantage of his presence at this university to study these "amazing bacteria" that he had previously seen.

He believed that "it would be like meeting a human being on Mount Everest."

In the fall of 2018, he received his first package that Professor Groh sent him to the University-run Lawrence Berkeley National Laboratory's Genome Sequencing Institute.

The main difficulty was of a technical nature, which was to be able to provide an image of the entire bacteria, thanks to "three-dimensional microscopic analyses, with a stronger magnification".

The researcher had at the disposal of advanced technologies in the American laboratory, and he also received great financial support and the ability to benefit from the help of “expert researchers in genome sequencing,” he says.

His 3D images eventually enabled him to prove that all filaments do indeed belong to a single cell.

The novelty of this bacteria was not limited to its “giant size”, as it also turned out to be “more complex” than other bacteria, which the researcher sees as a “completely unexpected” discovery... that turns upside down a lot of knowledge available to date in biology. minute.”

"DNA usually floats freely in a bacteria cell, but in this bacterium it is compressed into small structures called dots, which are a kind of small membrane-enclosed sacs, which isolate the DNA from the rest of the cell," says Folan.

He explains that this division of DNA - the molecule that carries genetic information - is “characteristic of human, animal and plant cells...not of bacteria.”

Future research should clarify whether these properties are limited to Thiomargarita magnifica or are present in other bacteria, according to Olivier Gros.

Volan believes that "this bacterial giant is prompting a reconsideration of many of the bases of microbiology" and "provides the opportunity to understand how complexity arises in living bacteria."

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