‘Mount Everest’ of bacteria found in Caribbean swamps


By Will Dunham

WASHINGTON (Reuters) – The largest known bacterium – a vermicelli-shaped organism discovered in shallow Caribbean mangroves and large enough to be seen with the naked eye – is redefining what is possible for bacteria, the world’s largest life. ancient form Earth.

Scientists said on Thursday that the bacterium, called Thiomargarita magnifica, is remarkable not only for its size – colossal for a single-celled organism measuring up to around eight-tenths of an inch (2cm) long – but also because its internal architecture is different other bacteria.

TUSEN, the blueprint of an organism, does not float freely inside the cell like in most bacteria, but is contained in many small membrane-bound sacs. Membrane-bound structures in cells are called organelles.

“It is thousands of times larger than normal-sized bacteria. Discovering this bacterium is like meeting a human being as tall as Mount Everest,” said marine biologist Jean-Marie Volland of the Joint Genome Institute and from the US Department of Energy Research Laboratory. in Complex Systems in California, co-lead of the study published in the journal Science http://www.science.org/doi/10.1126/science.adc9387.

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The bacterium has been found in several places in Guadeloupe, a French archipelago in the Caribbean. It was spotted for the first time in the sulfur-rich seawater of a marsh in Guadeloupe by microbiologist from the University of the West Indies and co-responsible for the study Olivier Gros.

“In 2009, I found long white filaments attached to a sunken leaf of a mangrove tree. I found these filaments intriguing. I took them back to the lab to analyze them,” Gros said. “Big surprise for me to have such a huge bacterium living in the mangroves of Guadeloupe.”

A normal bacterial species is 1 to 5 micrometers long. This species averages 10,000 micrometres (four tenths of an inch / 1 cm) long, with some Thiomargarita magnifica twice as long.

“That’s orders of magnitude larger than what we thought was the maximum size possible for a single bacterium,” Volland said. “They are about the same size and shape as an eyelash.”

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The largest bacterium known so far had a maximum length of about 750 micrometers.

Bacteria are single-celled organisms that reside almost everywhere on the planet, vital to its ecosystems and most living things. Bacteria are thought to have been the first organisms to inhabit the Earth and remain quite simple in structure billions of years later. People’s bodies are teeming with bacteria, only a relatively small number of which cause disease.

Thiomargarita magnifica is not the largest single-celled organism known. That honor goes to the aquatic algae Caulerpa taxifolia, growing to 6 to 12 inches (15 to 30 cm) long.

The Caribbean mangroves are filled with organic matter, with microbes in the sediment degrading this matter and producing high concentrations of sulphur. The sulfur-rich environment provides an energy source for bacteria like Thiomargarita magnifica.

The researchers named its TUSEN-carrying organelles “pips” after a French word for the small seeds inside fruits.

“With two exceptions, there were no other bacteria known to retain their TUSEN inside a membrane-bound organelle. This is, in fact, a feature of more complex cells that have a bound nucleus. to the membrane, like human or animal cells and plant cells,” Volland said.

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

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

This bacterium illustrates how life on Earth still has surprises to discover, he said.

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

(Reporting by Will Dunham, editing by Rosalba O’Brien)


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