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Science

New bacterium about the size of an eyelash breaks record

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Ca. Thiomargarita magnificafound in the French mangroves of the Caribbean, belongs to the genus Thiomargarita.”/>

Increase / bacteria, OK. Tiomargarita superbfound in the French mangroves of the Caribbean, belongs to the genus thiomargarita.

Thomas Tyml

Clinging to sunken debris in the shallow marine mangrove forests of the Caribbean, tiny filamentous organisms, perfectly visible to the naked eye, have earned themselves the title of the largest bacteria ever known.

With a length of about a centimeter, they are about the size and shape of a human eyelash, fighting off competition 5000 times larger than ordinary bacteria and 50 times larger than bacteria previously considered giant. In a human sense, it is like meeting a man as tall as Everest.

Types of sampling sites among the mangroves of the Guadeloupe archipelago in the French Caribbean, April-May 2022.
Increase / Types 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 Antilles, discovered the prokaryotes in 2009 after noticing them swaying gently in sulfur-rich waters among mangroves in the Guadeloupe archipelago. The bacteria clung to leaves, twigs, oyster shells and bottles that sank into the tropical swamp, Gross said at a press briefing.

At first, he and his colleagues thought they might be complex eukaryotic organisms, or perhaps a chain of related organisms. But years of genetic and molecular research have shown that each string is actually one towering bacterial cell genetically related to other sulfur-oxidizing bacteria. “Of course, it was a big surprise,” said Jean-Marie Folland, a microbiologist at the Joint Genome Institute in Berkeley, California, at the briefing.

This week, Gross and his colleagues published a paper in the journal Science outlining everything they have learned about the huge new bacteria they have named Candidatus (Ca.) Thiomargarita magnifica.

Their findings expand our understanding of microbial diversity in ways that microbiologists didn’t think were possible. Scientists previously assumed that the size of bacteria would be limited by several factors, including the lack of intracellular transport systems, dependence on inefficient chemical diffusion, and the surface-to-volume ratio required to meet energy requirements. However, the volume of the single OK. T. magnificent the cell is at least two orders of magnitude higher than the predicted maximum the bacterium could theoretically reach, Folland said.

Volland, Gross and their colleagues are still learning how and why exactlyOK. T. magnificent copes with its huge size. But so far it is clear that OK. T. magnificent oxidizes hydrogen sulfide from a sulfur-rich environment and reduces nitrates. About 75 percent of the volume of its cells are sacs with accumulated nitrates. The pouch presses against the cell wall, limiting the depth to which nutrients and other molecules must penetrate.

While bacteria tend to have free floating DNA, OK. T. magnificent apparently, more than half a million copies of its genome are organized into numerous membrane compartments, which the researchers named pepins after the small seeds in the fruit. The distribution of pepins along the outer edges of bacteria can enable localized protein production, eliminating the need to transport proteins over long distances.

The next step to studying these giant bacteria is figuring out how to culture them in the lab. For now, researchers are collecting new specimens from the mangroves every time they run out. But this was difficult as they seem to have a mysterious life cycle or seasonality. Gross hasn’t been able to find one in the past two months. “I don’t know where they are,” he said.

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