Scientists discovered the world’s largest known bacteria, which comes in the form of white filaments the size of human eyelashes, in a swamp in Guadeloupe.
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. The fine white threads were discovered on the surfaces of decaying mangrove leaves in shallow tropical marine swamps.
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The finding came as a surprise because, according to models of cellular metabolism, bacteria simply shouldn’t grow that big. Previously, scientists had suggested a maximum possible size limit about 100 times smaller than the new species.
“To put it in context, it would be like a human meeting another human as high as Mount Everest,” said Jean-Marie Volland, a scientist at Lawrence Berkeley National Laboratory who co-authored the study.
The organism was discovered by Olivier Gros, professor of marine biology at the Université des Antilles in Guadeloupe, while looking 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 threads were single cells. 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 membrane-bound compartments throughout the 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 scattered throughout each cell, making it extraordinarily complex.
Scientists are still not sure how bacteria evolved to be so large. One possibility is that it has adapted to avoid predation. “If you grow hundreds or thousands of times bigger than your predator, you can’t be consumed by your predator,” Volland said.
However, getting big would mean losing some of the bacteria’s traditional advantages, including the unique ability to move around and colonize new niches. “By leaving the microscopic world, these bacteria have definitely changed the way they interact with the environment,” Volland said.
The bacteria have yet to be found elsewhere – and they disappeared from the original location when the researchers returned recently, perhaps because they are seasonal organisms. But in the paper, published in the journal Science, the authors conclude that the finding “suggests that large, more complex bacteria may be hiding in plain sight.”
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