Enlarge / Bacteria, Ca. Magnificent Thiomargarita, discovered in the mangroves of the French Caribbean is a member of the genus Thiomargarita.
Thomas Tyml
Clinging to the sunken remains in the shallow marine mangrove forests of the French Caribbean, small thread-like organisms, perfectly visible to the naked eye, have earned the title of the largest bacterium ever known.
Measuring about an inch long, they are about the size and shape of a human eyelash, eliminating competition at 5,000 times the size of bacteria in the garden variety and 50 times the size of bacteria previously considered giants. . In human terms, this is similar to meeting a person as tall as Everest.
Enlarge / Views of sampling sites among the mangroves of the Guadeloupe archipelago in the French Caribbean, April-May 2022.
Pierre-Yves Pascal
Olivier Gros, a biologist at the University of the West Indies, discovered prokaryotes in 2009, noticing that they gently swayed in the sulfur-rich waters among the mangroves of the Guadeloupe archipelago. Bacteria clung to leaves, branches, oyster shells and bottles that sank in the tropical swamp, Gros said at a news conference.
He and his colleagues first thought that they could be complex eukaryotic organisms or perhaps a chain of linked organisms. But years of genetic and molecular research revealed that each string is, in fact, a very high bacterial cell, genetically related to other sulfur oxidizing bacteria. “Of course, it was quite a surprise,” Jean-Marie Volland, a microbiologist at the Joint Genome Institute in Berkeley, California, said at the briefing.
This week, Gros and his colleagues have published an article in Science outlining everything they have learned about the new and huge bacteria, which they have dubbed Candidatus (Ca.) Thiomargarita magnifica.
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Their findings broaden our understanding of microbial diversity in ways that microbiologists did not think possible. Scientists previously hypothesized that the size of bacteria would be limited by several factors, including the lack of intracellular transport systems, reliance on inefficient chemical diffusion, and a surface-to-volume ratio needed to meet energy needs. However, the volume of a single Ca. The T. magnifica cell is at least two orders of magnitude higher than the maximum predicted a bacterium can theoretically reach, Volland said.
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Filaments of Ca. Thiomargarita magnifica.
Jean Marie Volland
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Filaments of Ca. Thiomargarita magnifica.
Jean Marie Volland
Volland, Gros and his colleagues are still learning how and why exactly Ca. T. magnifica manages its massive size. But so far it is clear that Ca. T. magnifica oxidizes hydrogen sulfide from its sulfur-rich environment and reduces nitrate. About 75 percent of its cell volume is a bag of stored nitrate. The sac is crushed against the cell envelope, limiting the depth that nutrients and other molecules need to diffuse.
While bacteria tend to have freely floating DNA, Ca. T. magnifica appears to have more than half a million copies of its genome grouped in numerous membrane-bound compartments that researchers called cucumbers, after small seeds of the fruit. The distribution of cucumbers along the outer edges of the bacterium could allow localized protein production, eliminating the need to transport proteins over long distances.
The next step in studying these gigantic bacteria is for scientists to figure out how to grow them in labs. So far, researchers have collected new specimens from the mangrove forests each time they run out. But, this has been tricky as they seem to have a mysterious life cycle or seasonality. Gros has not been able to find any for two months. “I don’t know where they are,” he said.