It is an organism of 9 millimeters on average. The size of a small fingernail, not much on our human scale, but a revolution on the scale of microorganisms. The largest bacterium in the world was discovered somewhat by chance in Guadeloupe, in the mangroves, and it is visible to the naked eye. “Meeting this bacterium is a bit like discovering a human as tall as Mount Everest,” compares Jean-Marie Volland, co-author of the study published Thursday, June 23 in Science.
Named Thiomargarita magnifica, this bacterium looks like white filaments. It was observed on decaying leaves in water more than ten years ago. But it took time to be sure that it was indeed a bacterium. All specialists agree that its size is beyond comprehension and the limits of what was previously thought possible.
Encapsulated genetic material
This bacterium, like the vast majority, is unicellular. But normally, the genetic material of bacteria “floats” freely in their cytoplasm, like coins in a bag. Here, the immense bacterium has compartmentalized it in membranes, as one would store the budget of each expense in a different pocket. “It’s totally new and has never been observed in bacteria before,” rejoices the researcher in a video to present the work.
The study shows that the bacterium is active all along the filament, in these compartments, and not only at the ends where it grows and reproduces. “These compartments, which store DNA and ribosomes, function almost like autonomous organisms within the giant cell,” described in Science Petra Levin, an American biologist who was not involved in the study.
Its size and complex organization make Thiomargarita magnifica a rarity in the world of microorganisms. And ask: why has a bacterium become so large? Are there others before our eyes that we have never bothered to study?