Visible to the naked eye: giant bacterium discovered on Guadeloupe

Bacteria are thought of as tiny organisms, but they can also reach impressive sizes.

Visible to the naked eye: giant bacterium discovered on Guadeloupe

Bacteria are thought of as tiny organisms, but they can also reach impressive sizes. A research team in Guadeloupe found the evidence. They discover a bacterium that they can even grab with the tweezers.

In Guadeloupe, scientists have discovered the largest bacterium known to date. Thiomargarita magnifica is 5,000 times larger than average bacteria, measuring up to two centimeters in size, and has a more complex structure, according to a study published in the journal Science. It's shaped like an eyelash and turns microbiology on its head, said Olivier Gros, biology professor at the University of the Antilles and co-author of the study.

According to this, the bacterium can be "seen with the naked eye" and even "grasped with tweezers". The researcher first discovered the species in 2009 in the mangroves of the French overseas territory in the Caribbean. "At first I thought it was anything but a bacterium. Because something two centimeters tall can't be a bacterium," Gros said. However, with the help of electron microscopy, it quickly turned out that it was a bacterial organism.

A colleague of Gros found that it belonged to the Thiomargarita family, a previously known genus of sulfur bacteria that use sulfides to grow. Further findings by a scientist at the CNRS research center in Paris indicated that it was "a single cell," explained Gros.

A first attempt to publish in a scientific journal was canceled due to the lack of convincing photographic evidence. Only the young researcher Jean-Marie Volland at the University of California, with financial support and 3D microscopes, was able to produce a convincing representation of the giant bacterium. In human proportions, the new discovery is as colossal in relation to its peers as "if a human were to meet someone the size of Mount Everest," Volland said.

He made another interesting discovery: Normally, the DNA of a bacterium floats freely in the cell. However, in the newly discovered species, it's encased in small structures surrounded by a membrane, he explained. This is "usually a characteristic of human, animal and plant cells, complex organisms (...), but not of bacteria".

The researchers now want to find out whether this type of DNA is only found in Thiomargarita magnifica or whether it can also be found in other types of bacteria.

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