Scientists have discovered the world's largest known bacterium, which comes in the form of white filaments the size of human eyelashes, in a swamp in Guadeloupe.
The strange organism Thiomargarita magnifica, which is about 1 cm long, is roughly 50 times larger than all other known giant bacteria and the first to be seen with the naked eye. The thin white strands were discovered on the surfaces of decaying mangrove leaves in shallow tropical marine marshes.
The discovery was a surprise because bacteria should not grow this big according to models of cell metabolism. The upper possible size limit was proposed by scientists, about 100 times smaller than the new species.
It would be like a human encountering another human as tall 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, a marine biology professor at the Universit des Antilles in Guadeloupe, while searching for symbiotic bacteria in the mangrove ecosystem.
Gros said when I saw them, I thought they were strange. The lab first conducted microscopic analyses to determine whether the strands were single cells. Closer inspection revealed a strange internal structure. The DNA floats freely inside the cell, and is found in most bacteria. Thiomargarita magnifica appears to keep its DNA organized inside membrane-bound compartments throughout the cell. This is very unexpected for a bacterium, said Volland.
The bacterium was found to contain three times as many genes as most bacteria and hundreds of thousands of genome copies spread throughout each cell, making it unusually complex.
Scientists are not sure how the bacteria evolved to be so big. One possibility is that it adapted to evade predation. If you grow hundreds or thousands of times bigger than your predator, you can't be eaten by your predator, said Volland.
However, becoming big would have resulted in the loss of some of the traditional advantages of the bacteria, including being uniquely able to move around and colonise new niches. The bacteria have changed the way they interact with their environment by leaving the microscopic world, said Volland.
The bacteria have not yet been found in other locations and had disappeared from the original site when the researchers returned recently, perhaps because they are seasonal organisms. The authors conclude that the discovery suggests that large and more complex bacteria may be hiding in plain sight, according to the paper published in the journal Science.