Scientists discover "Mount Everest" of bacteria in Caribbean swamps

Scientists discover “Mount Everest” of bacteria in Caribbean swamps

The largest known bacterium – a vermicelli-shaped organism discovered in shallow mangrove swamps in the Caribbean and large enough to be seen with the naked eye – redefines what is possible for bacteria, the earth’s oldest life form.

Researchers said on Thursday that the bacterium, called Thiomargarita magnifica, is remarkable not only for its size – colossal for a single-celled organism up to about 2 cm long – but also because its internal architecture differs from other bacteria.

The DNA, a drawing of an organism, is not free-flowing inside the cell as in most bacteria but is found in many small membrane-bound sacs. Membrane-bound structures in cells are called organelles.

“It is thousands of times larger than ordinary bacteria. Discovering this bacterium is like meeting a human as tall as Mount Everest,” says marine biologist Jean-Marie Volland at the US Department of Energy’s Joint Genome Institute and Laboratory for Research. in Complex Systems, California, a co-author of the study published in the journal Science.

The bacterium has been found in several places in Guadeloupe, a French archipelago in the Caribbean. It was first discovered in the sulfur-rich seawater of a Guadeloupe swamp by the Université des Antilles microbiologist and study leader Olivier Gros.

“In 2009, I found long white filaments attached to a fallen leaf of a mangrove tree. I thought such filaments were exciting. I took them back to the lab to analyze them,” Gros said. “Great surprise for me to have such a huge bacterium living in the mangrove forests of Guadeloupe.”

A normal bacterial species is 1-5 micrometers long. This species is on average 10,000 micrometers (1 cm) long, with some Thiomargarita magnifica twice as long.

“These are orders of magnitude larger than we thought were the maximum possible size for a single bacterium,” said Volland. “They have about the same size and shape as an eyelash.”

The largest known bacterium to date had a maximum length of around 750 micrometers.

Bacteria are unicellular organisms found almost everywhere on the planet, crucial to its ecosystem and most living things. Bacteria are believed to have been the first organisms to inhabit the earth and remain fairly simple in structure billions of years later. Human bodies are teeming with bacteria, only a relatively small number of which cause disease.

Thiomargarita magnifica is not the largest known unicellular organism. That honor goes to the water alga Caulerpa taxifolia, which grows 15-30 cm long.

Caribbean mangrove swamps are packed with organic material, with microbes in the sediment that break down this material and produce high concentrations of sulfur. The sulfur-rich environment offers an energy source for bacteria such as Thiomargarita magnifica.

The researchers named its DNA-bearing organelles “pepins” after a French word for small seeds inside fruits.

“Apart from two exceptions, there were no other bacteria known to hold their DNA inside a membrane-bound organelle. It is actually a property of more complex cells that have a membrane-bound nucleus, such as human or animal cells, and plant cells,” said Volland.


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Mapping of its genome showed that Thiomargarita magnifica has lost some genes necessary for cell division and has more than the usual number of copies of genes responsible for cell elongation.

“This may partly explain why the cell grows into such an elongated filament. The genome is also very large and contains three times the average number of genes that are usually found in bacteria. Half of these genes we have no idea what they are for,” he said. Volland.

This bacterium illustrates how life on earth still has surprises waiting to be discovered, he said.

“Life is fascinating, very versatile and very complex,” Volland added. “It’s important to be curious and have an open mind.”

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