Scientists have discovered the largest known bacterium in the world, which comes in the form of white filaments the size of human eyelashes, in a Guadalupe swamp.
At about 1 cm long, the strange organism, Thiomargarita magnifica, is about 50 times larger than all other known giant bacteria and the first to be visible to the naked eye. Thin white threads were discovered on the surface of decaying mangrove leaves in shallow tropical marine swamps.
The discovery came as a surprise because, according to cellular metabolism models, bacteria simply shouldn’t grow as much. Previously, scientists had suggested a possible higher size limit about 100 times smaller than the new species.
“To put it in context, it would be like a human encountering another human as tall as Everest,” said Jean-Marie Volland, a Lawrence Berkeley National Laboratory scientist who co-authored the study.
Thiomargarita magnifica has been found to contain three times more genes than most other bacteria. Photography: Vollard et al.
The organism was discovered by Olivier Gros, a professor of marine biology at the Université des Antilles de Guadalupe, while searching for symbiotic bacteria in the mangrove ecosystem.
“When I saw them, I thought, weird,” Gros said. The lab first performed microscopic analyzes to establish that the chains were individual cells. A closer inspection also revealed a strange internal structure. In most bacteria, DNA floats freely within the cell. Thiomargarita magnifica appears to keep its DNA more organized within the compartments attached to the membrane of the entire cell. “And that’s very unexpected for a bacterium,” Volland said.
The bacterium was also found to contain three times as many genes as most bacteria and hundreds of thousands of copies of the genome spread throughout each cell, making it unusually complex.
Scientists are still not sure how the bacteria evolved to be so large. One possibility is that it has adapted to evade predation. “If you grow hundreds or thousands of times bigger than your predator, you can’t be consumed by your predator,” Volland said.
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However, growing up would have meant losing some of the traditional benefits of bacteria, including the unique ability to move and colonize new niches. “Coming out of the microscopic world, these bacteria have definitely changed the way they interact with their environment,” Volland said.
The bacteria have not yet been found elsewhere and had disappeared from the original site when the researchers recently returned, perhaps because they are seasonal organisms. But in the article, published in the journal Science, the authors conclude that the discovery “suggests that larger, more complex bacteria may be hidden from view.”