“Thiomargarita magnifica”, a bacterium that shakes the codes of microbiology.
It can be caught with a tweezers: the world’s largest bacterium , 5,000 times larger than its congeners and with a more complex structure, was discovered on the island of Guadeloupe in the French West Indies, according to a study published Thursday in the journal Science .
“Thiomargarita magnifica” measures up to two centimeters, looks like an eyebrow and shakes the codes of microbiology, Olivier Gros, professor of biology at the University of the Antilles, co-author of the study , told AFP .
In his laboratory on the Fouillol campus, in the French commune of Pointe-à-Pitre, in Guadeloupe , the researcher proudly displays a test tube containing small white filaments.
When the average size of a bacterium is two to five micrometers, it “can be seen, I can catch it with a tweezers!” he says.
In the mangroves of Guadalupe , the researcher observed the microbe for the first time, in 2009. “At first I thought it was anything but a bacterium, that couldn’t be,” he says.
Very soon, cell description techniques with an electron microscope showed that it is a bacterial organism. But at this size, Gros says, “we weren’t sure it was a single cell,” since a bacterium is a single-celled organism.
A biologist from the same laboratory reveals that it belongs to the Thiomargarita family , an already known bacterial genus that uses sulfides to develop. And work carried out in Paris by a CNRS researcher suggests that it is “one and the same cell”, says Gros.
It was not easy to publish about her in scientific journals
Convinced of their finding, the team tries to make a first publication in a scientific journal, but they do not succeed.
“They answered us: it is interesting, but we lack information for us to believe them”, because the test was not very strong in terms of image, says the biologist.
Jean-Marie Volland appears, a young post-doctorate from the University of the West Indies, who will become the first author of the study published in Science .
The importance of discovery
Since he did not obtain the position of research professor in Guadeloupe , this man in his thirties traveled to the United States, where he was recruited by the University of Berkeley. Traveling to the United States, he planned to study “the incredible bacteria” that he already knew well.
“It would be like finding a human as high as Everest,” he said.
In the fall of 2018, he receives a first package sent by Professor Gros at the University-run Lawrence Berkeley National Laboratory Genome Sequencing Institute.
The challenge was essentially technical: to achieve an image of the bacterium as a whole, thanks to “three-dimensional microscopy analysis” and with the highest possible magnification.
In the American laboratory, the researcher had highly sophisticated techniques. Without forgetting important financial support and “access to expert researchers in genome sequencing”, acknowledges the scientist, who describes this US-Guadalupan collaboration as a “success story”.
Its 3D images make it possible to prove that the entire filament is a single cell.
In addition to its “gigantism”, the bacterium is also “more complex” than its congeners: a “totally unexpected” discovery, which “quite shakes up knowledge in microbiology”, says the researcher.
“When generally in bacteria the DNA floats freely in the cell, in these it is compacted into small structures, like small bags surrounded by a membrane, which isolate the DNA from the rest of the cell, says Jean-Marie Volland.
This compartmentalized form of DNA is “a characteristic of human, animal, plant cells… but by no means of bacteria .”
Future research will have to say if these characteristics are typical of “Thiomargarita magnifica” or if they are also found in other species of bacteria, according to Olivier Gros.
“This bacterial giant questions many established rules in microbiology” and “offers us the opportunity to observe and understand how complexity emerges in a living bacterium,” concluded Jean-Marie Volland.