'Everest of bacterium' visible to naked eye discovered in Caribbean mangrove swamps

Scientists have discovered a new bacterium that is visible to the naked eye, branding it the biggest in the world.

Thiomargarita magnifica was found in the shallow mangrove swamps of the Caribbean, and has meant scientists are now redefining what is possible for bacteria.

The single-celled organism, which cannot cause disease, measures up to around two centimetres long and is contained within small membrane-bound sacs.

"It is thousands of times larger than regular-sized bacteria. Discovering this bacterium is like encountering a human being as tall as Mount Everest," said marine biologist Jean-Marie Volland, who published a study into the life-forms.

"It is orders of magnitude bigger than what we thought was the maximum possible size for a single bacterium… They are about the same size and shape of an eyelash."

They were found in a number of areas in Guadeloupe in the Caribbean, in sulfur-rich seawater, by Universite des Antilles microbiologist and study co-leader Olivier Gros.

He said: "In 2009, I found long white filaments attached to a sunken leaf of a mangrove tree. I found such filaments intriguing. I brought them back to the lab to analyse them.

"Big surprise for me to have so huge a bacterium living in the mangroves of Guadeloupe."

An average bacterial species measures between one and five micrometres in length (equal to 0.001 mm), but this species measures 10,000 micrometers (four-tenths of an inch or one cm), with some twice that long.

Until now, the largest known bacterium was around 750 micrometres.

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Though long, Thiomargarita magnifica is not the largest-known single-celled organism on Earth, with aquatic alga Caulerpa taxifolia taking the top spot at 15 to 30cm long.

Mr Volland added that the new bacteria shows how some life on Earth is still awaiting discovery, saying: "Life is fascinating, very diverse and very complex. It's important to stay curious and have an open mind."