ABOVE: Single filament of Thiomargarita magnifica Jean-Marie Volland

Nearly 350 years ago, Antoni van Leeuwenhoek needed a homemade microscope to see bacteria that floated in a single drop of rainwater. A study published in Science yesterday (June 23) now documents a bacterium that doesn’t require such a device to be seen: Thiomargarita magnifica, or “magnificent sulfur pearl,” which was first sampled in the swampy, sulfurous waters surrounding a mangrove forest in the Caribbean archipelago of Guadeloupe. It’s the largest bacterium found to date.

“It is orders of magnitude bigger than what we thought was the maximum possible size for a single bacterium,” Jean-Marie Volland, a marine biologist at the Lawrence Berkeley National Laboratory and study coauthor, tells Reuters. “They are about the same size and shape of an eyelash.”

When study coauthor Olivier Gros, a biologist at the University of the French West Indies and Guiana, first saw the spaghetti-like organism clinging to submerged mangrove leaves, he thought it might be a type of fungus, reports the Associated Press. But DNA testing later revealed it to be a single-celled bacterium, which the authors write in their study is part of a group called large sulfur bacteria. According to The New York Times, T. magnifica has average filament lengths of 9,000 microns, with the largest spindles measuring 20,000 microns (about the diameter of a US penny). That’s in stark contrast to typical bacteria such as E. coli, which measures about 2 microns long. 

Scientists have assumed that the simplicity of bacterial structures kept them small, but the new research reveals that T. magnifica’s cell membranes have complex compartments that may help them to grow to larger sizes, reports the Times.

“It’s an amazing discovery,” Petra Levin, a microbiologist at Washington University in St. Louis who was not involved in the study, tells the Associated Press. “It opens up the question of how many of these giant bacteria are out there—and reminds us we should never, ever underestimate bacteria.”