Scientists have found a bacterium that is visible to the naked eye and can grow up to 2 cm. A record.
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, has been discovered in Guadeloupe, according to a study published Thursday in the Journal “Science”. Thiomargarita magnifica measuring up to 2 cm, looks like an eyelash and shakes up the codes of microbiology, as Olivier Gros, professor of biology at the University of the West Indies and co-author of the study, told AFP.
In his laboratory on the Fouillol campus in Pointe-à-Pitre, the researcher proudly displays a test tube with small white threads. If the average size of a bacterium is 2 to 5 microns, “You can see it with the naked eye, I can pick it out with tweezers!” he marvels.
In 2009, the researcher observed the microbe for the first time in the Guadeloupe mangrove.
First release cancelled
Cell description techniques using electron microscopy quickly show that it is in fact a bacterial organism. But at that size, says Professor Gros, “we had no certainty that it was a single cell” – a bacterium is a single-celled microorganism.
A biologist from the same lab reveals that it belongs to the family Thiomargarita, an already known genus of bacteria that uses sulfides for growth. And the work carried out in Paris by a CNRS researcher suggests that we are dealing with “one and the same cell”, explains the Pright Big.
Convinced of their discovery, the team attempts a first publication in a scientific journal, which fails. “We were told, ‘It’s interesting, but we don’t have the information to believe you,’ the evidence isn’t visually strong enough,” the biologist recalls.
“As High as Mount Everest”
Entering is Jean-Marie Volland, a young post-doctoral fellow from the University of the West Indies who will become first author of the study published in Science. Unable to get a teaching position in Guadeloupe, the 30-year-old flew to the United States, where he was recruited by the University of Berkeley. When he went there, he wanted to study the “incredible bacteria” with which he was already familiar.
“It would be like meeting a person as tall as Mount Everest,” he thought to himself. In autumn 2018 he received a first package from Pright Gros at the Genome Sequencing Institute of the university-run Lawrence Berkeley National Laboratory.
The challenge was essentially technical: succeed in reproducing an image of the bacterium as a whole thanks to “higher magnification three-dimensional microscopic analysis”. In the American laboratory, the researcher had advanced techniques. Without forgetting the considerable financial support and the “access to experienced researchers in genome sequencing”, the scientist recognizes this American-Guadeloupean collaboration as “Success Stories”.
A “completely unexpected” discovery
His 3D images finally allow proof that the entire filament is actually a single cell. In addition to its “giantism,” the bacterium also turns out to be “more complex” than its conspecifics: a “completely unexpected” discovery that “shattered a whole body of knowledge in microbiology,” testifies the researcher.
“Whereas in bacteria, the DNA normally swims freely in the cell, in bacteria it is condensed in small structures, so-called pips, a kind of membrane-enclosed bags that isolate the DNA from the rest of the cell,” develops Jean Marie Volland.
This compartmentalization of the DNA – the carrier molecule of the genetic information – is “a property of human, animal, plant cells … not of bacteria at all”. “This bacterial giant challenges many established rules of microbiology” and “offers us the opportunity to observe and understand how complexity arises in a living bacterium,” enthuses Jean-Marie Volland.
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